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COMMON BEAN (Phaseolus vulgaris L.) YIELD, ROOT GROWTH, AND N
FIXATION RESPONSE TO MOISTURE DEFICITS
by

Maurice D. Yabba

A DISSERTATION

Submitted to
Michigan State University
in partial fulfillment of the requirements
for the degree of

DOCTOR OF PHILOSOPHY

CrOp Physiology - Department of Crop and Soil Sciences
2001

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ABSTRACT
COMMON BEAN (Phaseolus vulgaris L.) YIELD, ROOT GROWTH, AND N
FIXATION RESPONSE TO MOISTURE DEFICITS
by

Maurice D. Yabba

Common bean (Phaseolus vulgaris L.) is grown on more than 12 million hectares
and constitutes the most important food legume for more than 500 million people in Latin
America, the Caribbean, and Africa, where it is often grown under moisture deficits in
soils with non-optimal pH. The objectives of this study utilized limiting and non-limiting
moisture regimes to determine (i) if selected genotypes of common bean exhibited
differences in drought resistance as measured by yield, (ii) if drought resistant genotypes
had differing root growth, and (iii) if genotypes differed for N fixation. Field studies
were conducted at the Agricultural Experiment Station in St. Croix, USVI in 1999 and
2000 to evaluate the effect of moisture deficits on seed yield. Yield of the nine genotypes

ranged from 142 to 1508 kg ha" in 1999 and 568 to 896 kg ha" in 2000. In both years,

yield was affected by infestations of common bacterial blight (Xanthomonas campestris
pv. phaseoli), Cercospora (Cercospora canescens), and N-deficiency. Geometric mean
ranked PR9603-22 and the nodulated (nod) and non-nodulated (nn) isolines of DOR 364,

among the top four genotypes with regard to drought resistance in 1999 and 2000. Root
length was quantified for 10 root width classes with diameters ranging from 0.01 - 4.5

mm. Plants in growth pouches (25.4 x 35.6 cm) were grown in the growth chamber

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containing half-strength Hoagland’s nutrient solution (control) or half-strength
Hoagland’s nutrient solution + 10’6 M (abscisic acid) ABA. The ABA treatment
significantly increased total root length (TRL), root length Of various root width classes,
and root and shoot dry weight. Generally, XAN 176 and SEAS had a higher TRL than
the other genotypes and both had the highest root and shoot dry weight. For plants grown
in polyvinyl chloride tubes [(PVC) 0.35 x 0.92 m], water deficit significantly reduced
root length in root width classes at all depths except 30.6 - 45.7 cm and reduced TRL by
approximately 75, 38, and 38% at depths of0 - 15, 15.1 - 30.5, and 0 - 92 cm,
respectively. The genotypes XAN 176 and SEAS were consistently among the lines
producing the greatest root length in both stress and non-stress environments.
Approximately 97 and 93% of all roots were in root classes 5 1 mm in diameter in plants
grown in growth pouches and PVC tubes, respectively. N fixation was estimated via the
N difference method, using non-modulating (rm) isolines of BAT 477 and DOR 364 as the
reference crops. Total N-fixed among the genotypes was low, ranging from no fixation (-
34.3 kg ha") to 19.9 kg ha". DOR 364 (nn) gave a higher estimate of N-fixation than did
BAT 477 (nn). BAT 477 (nodulated) was one of the genotypes with the highest root-N
concentrations as were the higher yielding genotypes XAN 176 and PR9603-22.
Nitrogen harvest index values among genotypes ranged from 7 to 76%. Nitrogen use
efficiency did not differ among irrigated and rainfed treatments in 1999 but was greater in
the irrigated treatment in 2000. Genotypes varied for yield, TRL, NUE, NHI, and N
fixation. Growth pouch and PVC studies identified XAN 176 and SEAS as having high
TRL, suggesting that growth pouches may be a viable method for assessing root growth

of differing lines.

In loving
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for the joy and happiness you brought into my life

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ACKNOWLEDGMENTS

I wish to express my heartfelt appreciation and gratitude to my major advisor, to
Dr. Eunice Foster. Her friendship, enthusiastic support, and energetic guidance were a
constant throughout my studies at MSU. The opportunity to share her ideas and working
methods has provided me with skills and knowledge that go beyond the degree obtained.

I extend my sincere appreciation to the members of my guidance committee: Dr.
James Beaver, Dr. Richard Harwood, Dr. James Kelly, Dr. Manuel Palada, and Dr. Ken
Poff for their time and suggestions to improve this work and my personal goals. I also
thank Dr. Peter Jeranyama for providing statistical help, priceless suggestions and
criticism on scientific writing, Mark Frahm for generously giving his valuable time to
helping me with WinRhizo, and Dr. James Jay and Dr. Richard Brandenburg for financial
support during critical times.

Many thanks to Brian Graff, Tom Galecka, Jon Dahl, Norman Blakeley, Jerry
Taylor, and Doug Bagdero for their help and assistance in many instances. The
assistance of Jennifer and Jeff from Michigan State University, Victor Almodovar,
Paulino Perez, Nelson Benitez, Raymond Armstrong, Allison Davis, Stafford Crossman,
and James Hunt from the University of the Virgin Islands, in several phases of the work
is gratefully appreciated. Their willingness to help will always be remembered.

A special thanks to all my colleagues and friends in the Department of Crop and
Soil Sciences, especially: Rita House and Darlene Johnson for being so supportive during

the passing of wife. Many thanks.

 

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This research was funded in part by the Bean Cowpea Collaborative Research
Support Program (MSU) and assistantships provided through the efforts of Dr. James Jay
of the Michigan State University College of Agriculture and Natural Resources and Dr.
Richard Harwood, C.S. Mott Chair of Sustainable Agriculture. Their financial support
allowed for the completion of the final requirements to obtain this degree.

A special thanks to the staff at the Michigan Early Elementary Center: Diane,
Kim, Rhonda, Gala, Kathy, Jennifer, and Sarah and a special thank you to Claudette

Mask for providing babysitting services so I can finish writing my dissertation.

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TABLES OF CONTENTS

LIST OF TABLES .............................................................................................................. x
LIST OF FIGURES ......................................................................................................... xvii
LITERATURE REVIEW .................................................................................................... 1
Introduction ............................................................................................................. 1
Diseases .................................................................................................................... 2
Drought ..................................................................................................................... 4
Roots ......................................................................................................................... 6
Nitrogen Fixation and its effect on drought resistance ............................................. 8
Literature cited ........................................................................................................ 11
CHAPTER 1

COMMON BEAN (Phaseolus vulgaris L.) YIELD UNDER HIGH pH, LIMITED
MOISTURE , AND LOW NITROGEN

Abstract ................................................................................................................... 19
Introduction ............................................................................................................ 20
Materials and Methods ........................................................................................... 21
Field study .................................................................................................. 21
Water regime .............................................................................................. 22
Plant material ......................................................................................... .....22
Experimental design ................................................................................... 23
Data collection ........................................................................................... .23
Moisture stress indices ............................................................................... 24
Results and Discussion ........................................................................................... 25
1999 ............................................................................................................ 25
2000 ............................................................................................................ 30
Effect of pH on yield of common bean ...................................................... 32
Nutritional and pathological problems ....................................................... 34
Conclusion .............................................................................................................. 35
Literature cited ....................................................................................................... 36
CHAPTER 2

ROOT LENGTH, SHOOT WEIGHT, AND ROOT LENGTH DENSITY IN COMMON

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BEAN (Phaseolus vulgaris L.)

Abstract .................................................................................................................. 50
Introduction ............................................................................................................ 5 1
Materials and Methods ........................................................................................... 53
Growth chamber study ............................................................................... 53
Glasshouse study ........................................................................................ 54

Root quantification ..................................................................................... 55
Results and Discussion ........................................................................................... 56
Root parameters: Growth chamber study ................................................... 56

Root parameters: Glasshouse ..................................................................... 59

Shoot and root dry weight and R\S ............................................................ 66
Control genotypic response ............................................................ 66

ABA genotypic response ................................................................ 67

PVC genotypic response ................................................................ .68

Conclusion .............................................................................................................. 71
Literature cited ........................................................................................................ 7 2

CHAPTER 3

NITROGEN FIXATION AND PARTITIONING OF NINE CARIBBEAN AND
CENTRAL AMERICAN COMMON BEAN (Phaseolus vulgaris L.) LINES GROWN
UNDER RAINFED AND GLASSHOUSE CONDITIONS

Abstract .................................................................................................................. .98
Introduction ............................................................................................................ 99
Materials and methods ......................................................................................... 100
Field Study ................................................................................................ 100

Plant material ............................................................................................ 101
Experimental design ................................................................................. 101

Data collection .......................................................................................... 102

N2 fixation ................................................................................................. 102
Glasshouse study ...................................................................................... 103
Statistics .................................................................................................... 103
Results and Discussion ......................................................................................... 103
Partitioning .......................................................... - ..................................... 103

Water effect .................................................................................. .l 03

Root-N concentration ................................................................... .1 04

Stem-N concentration ................................................................... 105

Leaf-N concentration .................................................................... 106
Reproductive-N concentration ...................................................... 107

Nitrogen harvest index .............................................................................. 108
Harvest index ............................................................................................ 1 10
Nitrogen use efficiency ............................................................................. 111
Nitrogen fixation ....................................................................................... 1 12
Conclusion ............................................................................................................ 114

viii

Literature cited ..................................................................................................... l 15

Summary and conclusions .................................................................................... 137
Appendix .............................................................................................................. .1 39
Appendix A .............................................................................................. J 39
Appendix B ............................................................................................... 143

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LIST OF TABLES
CHAPTER 1

Table 1. Characteristics of common bean genotypes grown in field experiments at the
Agricultural Experiment Station at the University of the Virgin Islands, Christiansted, St.
Croix, U.S.V.I. in 1999 and 2000 ....................................................................................... 4 0

Table 2. Days to flower (DF), days to physiological maturity (DPM), and days to seed
fill (DSF) of nine common bean (Phaseolus vulgaris L.) genotypes grown at the
Agricultural Research Station at the university of the Virgin Islands-St. Croix Campus,
U.S.V.I.

1 999 .................................................................................................................................... 41

Table 3. Yield under stress and nonstress treatments (kg ha"), combined yield (kg ha“),
percent yield reduction, geometric mean (GM), number of pods harvested per plot, and
pod weight per plot (g), of nine common bean (Phaseolus vulgaris L.) genotypes grown
at the Agricultural Research Station at the university of the Virgin Islands-St. Croix
Campus, U.S.V.I. 1999 ...................................................................................................... 42

Table 4. Common blight (CB) (Xanthomonas campestris pv. Phaseoli), Cercospora
(Cercospora canescens), and ozone rating of nine bean (Phaseolus vulgaris L.) genotypes
grown at the Agricultural Research Station at the University of the Virgin Islands-St.
Croix Campus, U.S.V.I. 1999. Scale 0 to 9 with 0 = no visual symptoms and 9 =

death ................................................................................................................................... 43

Table 5. Yield (Kg ha") under irrigated and rainfed conditions, combined yield (Kg ha“),
percent yield reduction, 50 seed weight, seed per pod, number of pods harvested, pod
weight, geometric mean (GM), drought susceptible index (D81), and stress tolerance
index (STI) of eight common bean (Phaseolus vulgaris L.) genotypes grown at the
Agricultural Research Station at the university of the Virgin Islands-St. Croix Campus,
U.S.V.I.

2000 .................................................................................................................................... 44

Table 6. Correlations of yield under stress, yield under non-stress, and combined yield
for stress and non-stress treatments to geometric mean (GM), drought susceptible index
(D81), and stress tolerance index (STI). Data from eight genotypes of common bean

(Phaseolus vulgaris L.) grown at the Agricultural Research Station at the University of

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CHAPTER 2

Table 1. Total root length (TRL) and root length (RL) (cm) of eight common bean
genotypes germinated in a germination chamber for 4 d at 25°C and transplanted to an
environmentally controlled grth chamber for 28 d at 23/20°C day/night temperatures
and a 15 h photoperiod and grown under control conditions in a half-strength Hoagland’s
solution or in 1045 M ABA solution. Roots were harvested at 14, 21, and 28 days after
transplanting (DAT) and divided into 10 classes based upon root diameter.

n=32 .................................................................................................................................. 78

Table 2. TRL (m) at each harvest date for eight genotypes of common bean (Phaseolus
vulgaris L.) plants germinated in a germination chamber for 4 d at 25°C and transplanted
to an environmentally controlled growth chamber for 28 d at 23/20°C day/night
temperatures and a 15 h photoperiod and grown under control conditions in a half-
strength Hoagland’s solution or in 10'6 M ABA solution. N = 4 79

Table 3a and b. Root length (RL) of nine different root width ‘classes of common bean
grown in 0.92 m polyvinyl chloride (PVC) tubes of 30 cm diameter in a glasshouse at
Michigan State University, East Lansing, M1. at 27°C i 2 day/night temperatures and a

15 h photoperiod under stressed and non-stressed moisture conditions. n = 27 ............... 80

Table 4. Total root length (m) (TRL) at 15.24 cm depth increments for nine common
bean genotypes grown in 0.92 m polyvinyl chloride (PVC) tubes of 30 cm diameter in a
glasshouse at Michigan State University, East Lansing, M1. at 27°C :1: 2 day/night
temperatures and a 15 h photoperiod under stressed and non-stressed moisture conditions.
11 = 6 .................................................................................................................................... 82

Table 5. Statistical significance from ANOVA for genotypes, water, and genotype x
water interaction for all root width classes and rooting depths of nine common bean
genotypes grown in 0.92 m polyvinyl chloride (PVC) tubes of 30 cm diameter in a
glasshouse at Michigan State University, East Lansing, M1. at 27°C 1 2 day/night
temperatures and a 15 h photoperiod under stressed and non-stressed moisture conditions.
n = 6 (genotypes), 27 (water), and 3 (genotype x water) ................................................... 83

Table 6. Statistical analysis from AN OVA for genotypic response of nine common bean
genotypes for all root width classes and rooting depths when grown in 0.92 m polyvinyl
chloride (PVC) tubes of 30 cm diameter in a glasshouse at Michigan State University,
East Lansing, M1. at 27°C i 2 day/night temperatures and a 15 h photoperiod under
stressed and non-stressed moisture conditions. 11 = 3 ........................................................ 84

Table 7. Combined root length (cm) from stressed and nonstressed moisture conditions

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of nine common bean (Phaseolus vulgaris L.) genotypes of root width class 3, 4, and 10
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chloride (PVC) tubes of 30 cm diameter in a glasshouse at Michigan State University,
East Lansing, M1. at 27°C 1 2 day/night temperatures and a 15 h photoperiod in stress
and non-stress conditions. 11 = 6 ........................................................................................ 85

Table 8. Combined root length (cm) of root width classes 1, 2, 3, 4, 5, 6, and 10 at depth
“D” (45.8 - 61 cm), from stressed and nonstressed moisture conditions of nine common
bean (Phaseolus vulgaris L.) genotypes grown in 0.92 m polyvinyl chloride (PVC) tubes
of 30 cm diameter in a glasshouse at Michigan State University, East Lansing, M1. at
27°C :1: 2 day/night temperatures and a 15 h photoperiod. n = 6 ...................................... 86

Table 9. Total RL (cm) of root width classes 1, 2, 3, 4, 5, and 10 at depth “B” (15.3 -
30.5 cm) for nine common bean (Phaseolus vulgaris L.) genotypes grown in 0.92 m
polyvinyl chloride (PVC) tubes of 30 cm diameter in a glasshouse at Michigan State
University, East Lansing, M1. at 27°C i 2 day/night temperatures and a 15 h photoperiod
under moisture stress conditions. 11 = 3 ............................................................................. 87

Table 10. Root length (cm) of nine common bean (Phaseolus vulgaris L.) genotypes of
root width classes 1, 2, 3, 4, and 10 at depth “B” (15.3 - 30.5 cm) grown in 0.92 m
polyvinyl chloride (PVC) tubes of 30 cm diameter in a glasshouse at Michigan State
University, East Lansing, M1. at 27°C 3: 2 day/night temperatures and a 15 h photoperiod
under moisture stress conditions. Means :t SE, n = 3 ....................................................... 88

Table 11. Root length (cm) for root width classes 1, 2, 3, 4, 5, 6, and 10 at a depth of
45.8 - 61 cm (D) for nine common bean (Phaseolus vulgaris L.) genotypes grown in 0.92
m polyvinyl chloride (PVC) tubes of 30 cm diameter in a glasshouse at Michigan State
University, East Lansing, M1. at 27°C i 2 day/night temperatures and a 15 h photoperiod
under moisture stress conditions. 11 = 3 ............................................................................. 89

Table 12. Total root dry weight (RDW), root length (RL), average root diameter (RD),
average root surface area (RSA), average root volume (RV), and root length density
(RLD), for all root width classes of common bean plants grown in 0.92 m polyvinyl
chloride (PVC) tubes of 30 cm diameter in a glasshouse at Michigan State University,
East Lansing, M1. at 27°C :1: 2 day/night temperatures and a 15 h photoperiod under
stressed and non-stressed conditions. it = 27 ..................................................................... 90

Table 13. Root length density (RLD) for nine genotypes of common bean (Phaseolus
vulgaris L.) plants grown in 0.92 m polyvinyl chloride (PVC) tubes of 30 cm diameter in
a glasshouse at Michigan State University, East Lansing, M1. at 27°C i 2 day/night
temperatures and a 15 h photoperiod under stressed and non-stressed moisture conditions
at two soil depths, 15.3 to 30.5 and 45.8 to 61 cm. 11 = 3 (stress and nonstressed RLD)
and 6 (combined RLD) ....................................................................................................... 91

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Table 14. Dry weight (g) of shoot and root and root\shoot ratio of eight common bean
genotypes germinated in a germination chamber for 4 d at 25°C and transplanted to an
environmentally controlled grth chamber for 28 d at 23/20°C day/night temperatures
and a 15 h photoperiod and grown under control conditions in half-strength Hoagland’s
solution or in 1045 M ABA solution. 11 = 32 ...................................................................... 92

Table 15. Shoot and root dry weight (g) and root/shoot ratio of eight common bean
genotypes germinated in a germination chamber for 4 d at 25°C and transplanted to an
environmentally controlled grth chamber for 28 d at 23/20°C day/night temperatures
and a 15 h photoperiod, grown in a half-strength Hoagland’s nutrient solution, and
sampled at 14, 21, and 28 DAT. n = 4. Control treatment ............................................... 93

Table 16. Shoot and root dry weight (g) and root/shoot ratio of eight common bean
genotypes germinated in a germination chamber for 4 d at 25°C and transplanted to an
environmentally controlled growth chamber for 28 d at 23/20°C day/night temperatures
and a 15 h photoperiod, grown in a 10'6 M ABA, and sampled at 14, 21, and 28 DAT. n
= 4. ABA treatment ........................................................................................................... 94

Table 17. Dry weight (g) of leaves, stems, reproductive parts, shoots, and root and
root/shoot ratio of nine common bean genotypes grown in 0.92 m polyvinyl chloride
(PVC) tubes of 30 cm diameter in a glasshouse at Michigan State University, East
Lansing, M1. at 27°C :1: 2 day/night temperatures and a 15 h photoperiod under stressed
and non-stressed moisture conditions. n = 27 .................................................................. 95

Table 18. Dry weight (g) of leaves, stems, reproductive parts, shoots, and root and
root/shoot ratio of nine common bean genotypes grown in 0.92 m polyvinyl chloride
(PVC) tubes of 30 cm diameter in a glasshouse at Michigan State University, East
Lansing, M1. at 27°C i 2 day/night temperatures and a 15 h photoperiod under stressed
and non-stressed moisture conditions. n = 6 ..................................................................... 96

Table 19. Dry weight (g) of leaves, stems, reproductive parts, shoots, and root and
root/shoot ratio of nine common bean genotypes grown in 0.92 m polyvinyl chloride
(PVC) tubes of 30 cm diameter in a glasshouse at Michigan State University, East
Lansing, M1. at 27°C :t 2 day/night temperatures and a 15 h photoperiod under stressed
and non-stressed moisture conditions. n = 3 ..................................................................... 97

CHAPTER 3

Table 1. The effect of moisture stress on root, stem, leaf, and reproductive structures-N
concentration (g kg") in common bean (Phaseolus vulgaris L.) grown at the Agricultural
Experiment Station at the University of the Virgin Islands in 1999 and 2000, under
irrigated and rainfed moisture conditions and in polyvinyl chloride (PVC) tubes in a
greenhouse at Michigan State University, East Lansing, MI. in 2000, under stressed and

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nonstressed moisture condition. N = 36 (UVI), N = 27 (PVC) ....................................... 120

Table 2. Root-N concentration (g kg") of nine common bean (Phaseolus vulgaris L.)
genotypes harvested at three grth stages (V3, R2, and R7) grown at the Agricultural
Experiment Station at the University of the Virgin Islands in 1999 under rainfed and
irrigated moisture conditions. N = 8 (combined), 4 (rainfed or irrigated) ....................... 121

Table 3. Root-N concentration (g kg") of nine common bean (Phaseolus vulgaris L.)
genotypes harvested at three growth stages (V3, R4, and R8) grown at the Agricultural
Experiment Station at the University of the Virgin Islands in 2000 under rainfed and
irrigated moisture conditions. N = 8 (combined), 4 (rainfed or irrigated) ........................ 122

Table 4. Stem-N concentration (g kg") of nine common bean (Phaseolus vulgaris L.)
genotypes harvested at three growth stages (V3, R2, and R7) grown at the Agricultural
Experiment Station at the University of the Virgin Islands in 1999 under rainfed and
irrigated moisture conditions. N = 8 (combined), 4 (rainfed or irrigated) ........................ 123

Table 5. Stem-N concentration (g kg") of nine common bean (Phaseolus vulgaris L.)
genotypes harvested at three growth stages (V 3, R4, and R8) grown at the Agricultural
Experiment Station at the University of the Virgin Islands in 2000 under rainfed and
irrigated moisture conditions and in polyvinyl chloride (PVC) tubes in a greenhouse at
Michigan State University, East Lansing, MI. in 2000, under stressed and nonstressed
moisture conditions. N = (UV I)8 (combined), 4 (rainfed or irrigated); (PVC) N = 6
(combined), 3 (stress or nonstress) ................................................................................... 124

Table 6. Leaf-N concentration (g kg") of nine common bean (Phaseolus vulgaris L.)
genotypes harvested at three growth stages (V3, R2, and R7) grown at the Agricultural
Experiment Station at the University of the Virgin Islands in 1999 under rainfed and
irrigated moisture conditions. N = 8 (combined), 4 (rainfed or irrigated) ........................ 125

Table 7. Leaf-N concentration (g kg") of nine common bean (Phaseolus vulgaris L.)
genotypes harvested at three growth stages (V3, R4, and R8) grown at the Agricultural
Experiment Station at the University of the Virgin Islands in 2000 under rainfed and
irrigated moisture conditions and in polyvinyl chloride (PVC) tubes in a greenhouse at
Michigan State University, East Lansing, MI. in 2000, under stressed and nonstressed
moisture conditions. N = (UVI) 8 (combined), 4 (rainfed or irrigated); (PVC) N = 6
(combined), 3 (stress or nonstress) ................................................................................... 126

Table 8a and b. Reproductive structures-N concentration (g kg") of nine common bean
(Phaseolus vulgaris L.) genotypes harvested at three growth stages (V3, R2, and R7)
grown at the Agricultural Experiment Station at the University of the Virgin Islands in
1999 under rainfed and irrigated moisture conditions. N = 8 (combined), 4 (rainfed or

‘ irrigated) ........................................................................................................................... 127

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Table 9. Reproductive structures-N concentration (g kg") of nine common bean
(Phaseolus vulgaris L.) genotypes harvested at three growth stages (V 3, R4, and R8)
grown at the Agricultural Experiment Station at the University of the Virgin Islands in
2000 under rainfed and irrigated moisture conditions and in polyvinyl chloride (PVC)
tubes in a greenhouse at Michigan State University, East Lansing, MI. in 2000, under
stressed and nonstressed moisture conditions. N = (UVI) 8 (combined), 4 (rainfed or
irrigated); (PVC) N = 6 (combined), 3 (stress or nonstress) ............................................. 129

Table 10. Nitrogen harvest index (N HI) of common bean (Phaseolus vulgaris L.) plants
grown under irrigated (nonstressed) and rainfed (stressed) moisture regime in a 1999 and
2000 field study at the Agricultural Experiment Station at the University of the Virgin
Islands-St. Croix campus. The NHI was computed as grams seed-N / grams total-N. N =
8 (combined), 4 (rainfed or irrigated) ............................................................................... 130

Table 11. Harvest index (HI) of nine common bean (Phaseolus vulgaris L.) plants grown
under irrigated and rainfed moisture regime in a 1999 and 2000 field study at the
Agricultural Experiment Station at the University of the Virgin Islands-St. Croix campus.
The HI was as gram seed DW / gram total DW. N = 8 (combined), 4 (rainfed or
irrigated) ........................................................................................................................... 131

Table 12. Nitrogen use efficiency (NUE) of common bean (Phaseolus vulgaris L.) plants
grown under irrigated and rainfed moisture regime in a 1999 and 2000 field study at the
Agricultural Experiment Station at the University of the Virgin Islands-St. Croix campus.
The NUE was computed as total g DW / total g N or g seed DW / g seed N.

N = 36 ............................................................................................................................... 132

Table 13. Nitrogen use efficiency (NU E) of nine common bean (Phaseolus vulgaris L.)
plants grown under irrigated and rainfed moisture regime in a 1999 field study at the
Agricultural Experiment Station at the University of the Virgin Islands-St. Croix campus.
The NUE was computed as total g DW / total g N or g seed DW / g seed N. g seed DW/
g seed N. N = 8 (combined), 4 (rainfed or irrigated) ....................................................... 133

Table 14. Nitrogen use efficiency (NUE) of nine common bean (Phaseolus vulgaris L.)
plants grown under irrigated and rainfed moisture regime in a 2000 field study at the
Agricultural Experiment Station at the University of the Virgin Islands-St. Croix campus.
The NUE was computed as total g DW / total g N or g seed DW / g seed N. g seed DW/
g seed N. N = 8 (combined), 4 (rainfed or irrigated) ....................................................... 134

Table 15. Nitrogen fixed (kg ha") from common bean (Phaseolus vulgaris L.) plants
grown under irrigated and rainfed moisture regime in a 1999 and 2000 field study at the
Agricultural Experiment Station at the University of the Virgin Islands-St. Croix campus.
N-fixed was calculated by the difference method with DOR 364 (rm) and BAT 477 (nn)
as the reference crops. N = 36 ......................................................................................... 135

XV

Table 16. Nitrogen fixed (kg ha") of nine common bean (Phaseolus vulgaris L.)
genotypes grown under irrigated and rainfed moisture regime in a 1999 and 2000 field
study at the Agricultural Experiment Station at the University of the Virgin Islands-St.
Croix campus. N-fixed was calculated by the difference method with DOR 364 (rm) and
BAT 477 (nn) as the reference crops. N = 8 .................................................................... 136

xvi

 

 

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LIST OF FIGURES

Figure 1. Transpiration rate (means i SE, n = 36) of nine genotypes of common bean
grown under irrigated and rainfed moisture conditions at the Agricultural Experiment
Station at the University of the Virgin Islands. Vertical bars indicate standard error of the
mean at P s 0.01 ................................................................................................................. 46

Figure 2. Leaf temperature (means i SE, n = 36) of nine common bean genotypes using
a LiCor (L1 1600 Steady State) porometer grown under irrigated and rainfed moisture
conditions at the Agricultural Experiment Station at the University of the Virgin Islands.
Vertical bars indicate standard error of the mean ............................................................... 47

Figure 3. Leaf temperature (means t SE, n = 8) of nine common bean genotypes taken
with an infra-red thermometer at 57 DAP and grown under irrigated and rainfed moisture
conditions at the Agricultural Experiment Station at the University of the Virgin Islands.
Vertical bars indicate standard error ofthe mean at P s 01048

Figure 4. Sentry probe counts (means i SE, n = 36) of nine common bean genotypes
taken at a depth of 30.5 cm and grown under irrigated and rainfed moisture conditions at
the Agricultural Experiment Station at the University of the Virgin Islands. Vertical bars
indicate Standard error of the mean, significant at 57 DAP at P s 0.10 ............................. 49

xvii

 

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Literature review

Introduction

Common bean (Phaseolus vulgaris L.) is grown on more than 12 million hectares
and constitutes the most important food legume for more than 500 million people in Latin
America, the Caribbean, and Africa (Laing et al., 1983). It is a major source of dietary
protein throughout Latin America, the Caribbean and Eastern Africa, but per household
consumption is declining as population increases outdistance production (Graham and
Ranalli, 1997). Sixty percent of common bean production worldwide is grown under
water stress, making drought the second largest contributor to yield reduction after
disease (Singh, 1995). These constraints along with insect pests, heat stress, and low soil
fertility (CIAT, 1981) have prevented the realization of the crop’s yield potential and
have caused production instability from one year to the next.

The physiological mechanisms that may help impart drought tolerance in common
bean are still poorly understood. Carbon and nitrogen partitioning and remobilization,
stomatal closure, osmotic adjustment, and root development may all be involved (Levitt,
1980; Kramer, 1983; Blum, 1985, 1988; Hale and Orcutt, 1987; Ludlow and Muchow,
1990; Foster et al., 1995). Plants are usually classified as drought resistant or drought
susceptible based upon phenotypic plasticity and the level of yield reduction during water
stress (Levitt, 1980; Hale and Orcutt, 1987). Rapid, inexpensive, and reliable methods
for screening large amounts of germplasm would greatly aid efforts to develop drought

resistant lines and a better understanding of plant metabolic processes would enable a

more efficient approach to germplasm improvement (Wortmann et al., 1998).

The conditions under which this annual, predominantly self-pollinated legume is
grown are extremely variable. The diversity of conditions, coupled with highly specific
local preferences for particular seed types or colors have complicated attempts at bean
improvement (Graham and Ranalli, 1997). As a result, greatest progress has been made
in breeding for the resolution of disease, insect and nutritional constraints, with only
limited improvement in yield potential (Graham, 1978; Adams et al., 1985; Laing et al.,
1985; Gepts, 1988a; and Schoonhoven and Voysest, 1991).

Inadequate soil nitrogen availability has also been identified as a major constraint
to common bean production in Latin America and Afi'ica (Wortmann et al., 1998).
Unlike some legumes, common bean typically derives little of its nitrogen from the
atmosphere under low input agriculture although N2 fixation can be substantial if soil
phosphorus is adequate (Giller et al., 1998). Common bean is genetically variable in its
ability to obtain nitrogen from the soil, for N2 fixation, and for partitioning of nitrogen
(Graham, 1978; Rennie and Kemp, 1983).

Diseases

Diseases are the most important constraint to common bean production in Latin
America and Africa (CIAT, 1981; Beaver, 1995). More plant pathogens and more
virulent isolates of these pathogens exist in Latin America and Africa than in the
temperate regions of North America and Europe (Beebe and Pastor-Corrales, 1991;
Miklas et al., 1996). The prevalence and importance of each disease vary considerably
with locality, season, year, and cultivar, however, some diseasessuch as ashy stem blight

2

 

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(ASB) are major problems.
Ashy stem blight is caused by the fungus Macrophomina phaseolina (Tassi) Goid.
(Dhingra and Sinclair, 1977). Ashy stem blight is a warm-temperature pathogen of the
beans P. vulgaris and P. lunatus L., soybean (Glycine max L.), maize (Zea mays L.),
sorghum (Sorghum bicolor), and many other crops (Watanabe et al., 1970). The disease
occurs mainly in Latin America but also in other parts of the world such as Kenya,
Zambia, and Egypt (CIAT, 1981; Stoetzer, 1984). The disease is more prevalent and
damaging to common bean that are exposed to drought and warm temperatures (CIAT,
1989). There seems to be a relationship between ASB resistance and drought tolerance.
Two lines of P. vulgaris, BAT 477 and San Cristobal 83, appear to have both ASB
resistance and drought tolerance traits (personal communication, Dr. James Beaver).
Common bacterial blight (CBB), a systemic (Burkholder, 1921), seed-transmitted
(Aggour et al., 1989b) disease caused by Xanthomonas campestris pv. phaseoli (Smith)
Dye (ch) (Saettler, 1989; Schuster and Coyne, 1981) frequently and severely attacks
common bean grown in the tropics and subtropics (Singh and Munoz, 1999). Common
bacterial blight is widespread in Latin America, particularly in northwestern Argentina,
south central Brazil, Venezuela, Central America and Cuba, and coastal Mexico (Singh
and Munoz, 1999). Common bacterial blight attacks all aerial plant parts, including leaf
petioles, pods, and seeds, but the characteristic symptoms of chlorotic borders and
necrotic lesions are more severe and conspicuous on leaves of susceptible cultivars
(Singh and Munoz, 1999). Common bacterial blight can survive for months on plant
debris left on the soil and in seeds (Gilbertson et al., 1990). Heavy and early infection,

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high humidity, temperatures fluctuating between 20 and 25°C, and alternately dry and wet
weather can cause more than 40% yield loss in susceptible cultivars (Serracin et al.,
1991). Other factors influencing disease severity are photoperiod (Arnaud-Santana et al.,
1993a), inoculation method, source and type of inoculum, and bacterial. concentration
(Aggour et al., 1989a), and stage of crop maturity at infection (Coyne and Schuster,
1974).

Drought

White and Singh (1991) estimated that more than 60% of common bean grown in
Latin America, Afiica, and Asia suffer from water stress during crop growth. In Latin
America alone, where one third of the world’s common bean are produced, 93% of the
common bean growing areas experience moisture stress (Fairbaim, 1993). The intensity
of drought stress and the phenological stage of development at which drought occurs is
unpredictable and differs for each year and region. Thus, moisture stress influences crop
yield in different ways in different regions (Acosta-Gallegos and Adams, 1991).

Common bean are particularly susceptible to drought during flowering, with
significant flower and pod abortion occurring when water shortage occurs at this time
(Graham and Ranalli, 1997). Nunez-Barrios (1991) observed in common bean that water
deficit hastened flowering and seed fill but delayed leaf appearance. Rapid root
expansion was noted at the beginning of the water deficit period, and was followed by
root death and compensatory growth in deeper soil layers. Drought may be terminal,
where there is a gradual decrease of soil moisture as the plant matures, or intermittent in
which moisture stress persists for seven days or longer. Intermittent stress may occur in

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less than 7 days on course textured soils in the tropics (personal communication, Dr.
James Beaver) and may occur once or several times in the growing season (Levitt, 1972).
Drought resistance is defined by Hall (1993) as the relative yield of a genotype
compared to other genotypes subjected to the same dought stress. Drought resistance in
some species has been clearly demonstrated by the work on corn (Zea mays), sorghum,
wheat (Triticum aestivum L.), barley (Hordeum vulgare L.), and bean (Begg and Turner,
1976; Morgan, 1984; Turner, 1986; Acevedo,1987; Singh, 1989). Species differences in
drought resistance depend on the type of economic product of the species (Hall, 1993).
Species producing leafy vegetables, such as lettuce (Lactuca sativa), have little drought
resistance, and tuber crops, such as potato (Solanum tuberosum), are more resistant to
drought than leafy vegetables, but their yield and quality can be reduced by mild or
moderate drought (Hall, 2001). In contrast, hay crops such as alfalfa (Medicago sativa
L.) are even more drought resistant, and their yield is only reduced when drought
becomes moderate and where economic yield is a reproductive organ (Hall, 2001).
Resistance to drought depends on the stage of reproductive development, the type of
economic product, and whether the plant is determinate or indeterminate (Hall, 2001).
The mechanisms of drought resistance in crop plants have been divided into
several categories: drought escape, dehydration avoidance, dehydration tolerance,
feedforward responses, and water use efficiency (Kramer, 1980, 1983; Levitt, 1980;
Turner, 1986; Blum, 1988; Ludlow and Muchow, 1990; Hall, 2001). Drought escape is
the ability of a plant to escape drought by completing its life cycle during the favorable
moisture conditions prior to the onset of drought. Drought escape or evasion has

5

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sometimes been incorrectly equated to drought avoidance (Levitt, 1980; Blum, 198 8).
Dehydration avoidance is the ability of a plant to prevent water loss by stomatal closure
resulting in the maintenance of turgor during periods favoring high rates of transpiration.
Dehydration tolerance is the ability of a plant to withstand injury when plants are under
drought stress. F eedforward response (Hall, 2001 ), is the theory that roots sense difficult
conditions in the soil and send signals to the shoot that cause partial stomatal closure and
slow down leaf expansion before the supply of water or nutrients is affected (Passioura
and Stirzaker, 1993). Water use efficiency is the ratio of biomass production to
transpiration.

Roots

Roots play an important role in the growth and survival of plants during periods
of drought stress. Under drought, the root is characterized by a low root density in the
dry surface layer and a higher root proliferation in the deeper, wetter soil layers (Smucker
et al., 1991). Under non-stress conditions, roots proliferated in the soil zone with the
lowest soil water retention (Garay and Wilhelm, 1983). A root system that extends the
root zone to more fully extract available soil water has the potential to increase yield
under drought (Mambani and Lal, 1983.). Thus, water uptake and transport by roots are
very important, especially under water limiting conditions (Nguyen et al., 1997).

In common bean, differences in plant growth habit are mirrored by differences in
root morphology. Type 11 growth habit is characterized by an intermediate, upright plant
structure with reduced branching angle whereas type III habit is typical of an intermediate
prostrate sprawling plant structure (Brothers and Kelly, 1993). Type 11 plants develop a

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thick tap root which can exploit deeper soil levels where water is often stored and type 111
plants, exhibit a shallow expansive root morphology (Lynch and van Beem, 1993).

When the plant root is to be defined for breeding and genetic transformation work,
it must be recognized that the root can be described on the basis of its potential traits or
on the basis of its stress-induced dynamic response (Nguyen et al., 1997). When drought
stress develops, the root/shoot (R/S) ratio increases (Creelman et al., 1990; Leskovar and
Cantliffe, 1992). Most certainly root morphology and distribution change. These
changes may have a genetic basis and are the integrated expression of various adaptive
processes taking place in the root in response to plant water deficit and a drying soil
(Nguyen et al., 1997). Overall, the root traits of water uptake and root length have been
studied by many researchers and have strong potential for improvement through breeding
with the major limitation being the labor intensive screening for most root traits (Ingram
et al., 1994).

Root development and capacity of plants to absorb water are closely related. As
root width, depth, and branching increased, plant water stress decreased (Hurd, 1976).
Levitt (1972) observed that when ground water was available, deep rooted plants showed
greater drought avoidance than shallow rooted ones but they showed lower avoidance
when deeper soil moisture was not present. Rooting depth and resistance to water flow
within the root were important attributes of root systems when plants were grown in
drought-prone environments (Taylor, 1980). White et al. (1990) reported that drought
resistance in common bean was related to rooting depth.

Root architecture may also be important for mining minerals, nutrients, and water

7

 

 

 

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from the soil (Lynch and Van Beem, 1993). Fitter (1991) developed topological indices
to quantify root architecture in two-dimensions, ranging from a herringbone structure at
one extreme to a highly branched, dichotomous structure at the other extreme. Based on
comparisons of ecologically distinct species and simple modeling exercises, Fitter (1991)
proposed that root architecture may influence the efficiency of plant nutrient uptake.

Soil exploration by roots was associated with nutrient acquisition, especially in
the case of immobile nutrients such as phosphorus (Lynch and Van Beem, 1993).
Genetic differences in common bean were reported for root biomass, R/S ratio (Hannah et
al., 2000; Borch et al., 1999; Fawole etal., 1982; Stoffela et al., 1979a), and for root
biomass distribution among distinct root types (Stofella et al., 1979b).

Some researchers have shown that the ability of a rice (Oryza sativa L.) plant to
reach deep soil moisture or to penetrate compacted soils was linked with the capacity of
the plant to develop a few thick (lateral) and long root axes (Yoshida and Hasegawa,
1982; Ekanayake et al., 1985; Ingram et al., 1994; Yu et al., 1995). Thick roots persisted
longer and produced more and larger branch roots, thereby increasing root length density
(RLD, defined as the total root length divided by the volume of soil occupied by the root)
and water uptake (Fitter, 1991; Ingram et al., 1994).

Nitrogen Fixation and its effect on drought resistance

Nitrogen is the major limiting nutrient required for plant growth, especially in
agricultural systems (Date, 1973). It is an important component of the biochemical
constituents that enhance yield producing processes (Sinclair and Horie, 1989).
However, it is unclear whether moisture stress increases or decreases the sensitivity of

8

plants to nitrogen deficiency (Bennett et al., 1989). Plants in soils with low nitrogen have
reduced grth rates and a low root to shoot (R/S) ratio (Russel, 1977).

Common bean is considered to be an inefficient nitrogen fixer and requires N
fertilizer (Westennann et al., 1981). Inefficient nitrogen fixation in common bean is
mostly caused by the failure to establish efficient symbiosis in the field. Common bean
begins to fix nitrogen at a considerably later vegetative stage than other legumes, such
that periods of nitrogen stress are observed in common bean before nodules begin to
actively fix nitrogen (Westerrnann et al., 1981). To avoid periods of nitrogen stress in the
field, a starter fertilizer of N (40 kg ha") is usually applied (Sprent and Thomas, 1984).

The effect of water stress on nitrogen fixation, accumulation, partitioning, and
remobilization in common bean is well documented (Ramos et al, 1999; Serraj and
Sinclair, 1998; Castellanos et al., 1996; DeVries et al., 1989). Moisture stress affects the
total accumulation of nitrogen in many species, including cowpea (Vigna unguiculata
(Walp) L.), soybean, and common bean (Chapman and Muchow, 1985). Water stress
affects rhizobial survival and grth in soil, the formation and longevity of nodules,
synthesis of leghemoglobin and nodule function and is a major cause of nodulation
failure and low N2 fixation (Hungria and Vargas, 2000). Furthermore, severe water stress
may lead to irreversible cessation of N2 fixation (Sprent, 1971; Vincent, 1980; Walker
and Miller, 1986; Venkateswarlu et al., 1989; Guerin et al., 1991). Foster et al. (1995)
reported that a greater proportion of seed nitrogen was obtained from remobilized leaf
nitrogen under moderate moisture stress conditions in common bean, but not under severe
or prolonged moisture stress. Severe moisture deficits reduced N harvest index and N use

9

 

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efficiency. Foster et al. (1995) suggested that drought susceptible common bean
genotypes may utilize nitrogen less efficiently than resistant genotypes.

Determinate, early maturing type I bush habit common beans fix the least
nitrogen, while indeterminate climbing genotypes fix more nitrogen (Graham, 1978;
Rennie and Kemp, 1983; Gardezi et al., 1990). Generally, early maturing varieties are
inferior users of photosynthates for biological nitrogen fixation (Piha and Munns, 1987).
However, it has been suggested that some common bean varieties (most likely type 111)
can acquire enough nitrogen either through fixation or assimilation of mineral nitrogen
for the plants to achieve genetic yield potential under field conditions (Gardezi et al.,
1990 Westermann et al., 1981).

Nitrogen fixation should be emphasized as the dominant N input in farming
systems in the developing world , with fertilizer N usage in such systems focused on
more highly productive cash crops (Hungria and Vargas, 2000). Kennedy and Cocking
(1997) suggested that systems based upon N2 fixation are most promising and potentially
profitable in extensive rather than intensive agricultural systems, where erratic or
historically low rainfall and market changes can seriously impact the economics and
efficiency of fertilizer use. Appropriate soil management practices for the tropics (such
as no-till) which results in decreases in soil temperature and increases in soil moisture,

also benefit N2 fixation (Graham and Vance, 2000).

10

 

 

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Literature cited

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Acosta-Gallegos, J .A., and M.W. Adams. 1991. Plant traits and yield stability of dry
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Adams, M.W., D.P. Coyne, J.H.C. Davis, P.H. Graham, and CA. Francis. 1985.
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Aggour, A.R., D.P. Coyne, and AK. Vidaver. 1989a. Comparison of leaf and pod
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Aggour, A.R., D.P. Coyne, A.K. Vidaver, and KM. Eskridge. 1989b. Transmission of
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Beebe, SE, and MA. Pastor-Corrales. 1991. Breeding for disease resistance. In: ed. A.
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Begg, J .E. and NC. Turner. 1976. Crop water deficits. Adv. Agron. 282161-217.

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Burk}:

Casteli'

C hapn‘.

C TAT f

 

 

 

ClATtt

Coyne.

Creelm.

Date. R

DeVri e

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12

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13

Guerin.

Hale. Xi

 

Hall. A.

Hall. A.

Hanna

Hunt:

Lai

Guerin, V., D. Pladys, C. Trinchant, and J .M. Rigaud. 1991. Proteolysis and nitrogen
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Hungria, M., and M.A.T. Vargas. 2000. Environmental factors affecting N2 fixation in
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Ingram, K.T., F.D. Bueno, O.S. Namuco, E.B. Yarnboa, and CA. Beyrouty. 1994. Rice
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Kramer, P.J. 1983. Water relations of Plants. Academic Press, New York.
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14

Laing, D.R., P.G. Jones, and J.H.C. Davis. 1985. Common bean (Phaseolus vulgaris
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15

 

Seboc

Schus

Sena:

Sewn

Sinclz

Sing}

Sing}

311121

Smuc

water stress on nodule physiology and biochemistry of a drought tolerant cultivar
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16

 

Spren

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17

1.

White. I

il'ortn:

Yoshid

 

 

l'u. L.)

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for screening rice root penetration. Crop Sci. 35:684-687.

18

Con

condni
Study t
)idd.

monun

 

 

 

 

Chapter 1

Common bean (Phaseolus vulgaris L.) yield under high pH, limited moisture, and
low nitrogen.

Abstract
In many regions, common bean (Phaseolus vulgaris L.) is grown under rainfed
conditions where water deficits limit yield and cause instability of production. A field
study was conducted in 1999 and 2000 to evaluate the effect of limiting moisture on seed
yield. The study used a split plot arrangement in randomized complete block design with
moisture as the main plot, genotypes as subplot, and four replications. Combined yield of

the nine genotypes ranged from 142 to 1508 kg ha" in 1999 and 568 to 896 kg ha" in

2000. Mean yield of XAN 176, DOR 364 [nodulating (nod)], and PR9603-22 exceeded
1300 kg ha", despite infestations of common bacterial blight (Xanthomonas campestris
pv. phaseoli), Cercospora (C ercospora canescens), bean leafskeletonizer (near
Autoplasia spp), and ozone damage. In 1999, yield was reduced by 17 and 27% in the
non-nodulating isolines of BAT 477 (nod) and DOR 364 (nod), respectively due to
diseases. Days to flower (DF) ranged from 34 to 38 days after planting (DAP), and days
to maturity ranged from 69 ( to 75 DAP. The geometric mean ranked PR9603-22, XAN

176, and DOR 364 (nod) among the top genotypes for drought resistance.

19

500 m
them.
calorit
where

1991'.

comp

reduc

aSun

fungi

coun
Field
€n0r

Prod

198.

“6x1

Introduction

Common bean (Phaseolus vulgaris L.) is the principal food legume of more than
500 million people in Latin America, Asia, and Africa and for more than 100 million of
them, it is the leading source of dietary protein (CIAT, 1984) and an important source of
calories. Production of common bean, in many regions, occurs under rainfed conditions
where water deficit limits yield and causes instability of production (Ehleringer et al.,
1991; White et a1. 1994).

Common bean, a cheaper source of protein for developing countries in
comparison to animal protein, (Singh and Jambunathan, 1981) has been reported to
reduce the levels of cholesterol and blood glucose (Soni et al., 1982). There are also well
recognized shortcomings in consuming animal proteins in the developing countries, such
as unhygienic processing and storage and consequent microbial contamination (Singh and
Singh, 1992).

Common bean yields have been low, averaging less than 1 ton ha" in developing
countries to 2 tons ha" in developed countries (Laing et al., 1984; Adams, 1996). Yet
yields of 2.19 to 4.12 tons ha" are reported from experiment stations, indicating the
enormous gap between the potential and actual yield for this crop. The most important
production constraints in bean producing areas of the tropics are drought, diseases, insect
pests, stress caused by low rainfall (moisture and heat), and low soil fertility (CIAT,
1984). These constraints limit yield and cause production instability from one year to the
next. Drought is the major abiotic constraint, because almost all bean production in Latin
America, the Caribbean, and Africa occurs on dryland farming systems with frequent

20

 

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al.19

under
09nd
1980;
2001]
upon

Orcut

cuhit
under
COmn
Water
tttrn
limit:

L'nl )3!

USA

water deficit affecting more than 60% of the crop produced (White et al., 1990; Laing et
aL,1984)

The physiological mechanisms that help impart drought tolerance are still poorly
understood. Carbon and nitrogen partitioning and remobilization, stomatal closure,
osmotic adjustment, and root development may be involved (Kramer, 1980, 1983; Levitt,
1980; Turner, 1986; Blum, 1988; Ludlow and Muchow, 1990; Foster et al., 1995; Hall,
2001). Plants are usually classified as drought resistant or drought susceptible based
upon phenotypic plasticity and the level of yield reduction during water deficit (Hale and
Orcutt, 1987; Acosta-Gallegos, 1995).

Although agronomic practices are important under conditions of water deficit,
cultivar improvement is usually seen as the most promising approach to increase yields
under drought stress. Research has indicated that direct selection for seed yield in
common bean can be effective, although time-consuming and costly, both for well-
watered (N ienhuis and Singh, 1988; Singh et al., 1990) and water deficit conditions
(White et al., 1994). Thus, the objective of this study was to determine the effect of
limited moisture on seed yield in nine common bean genotypes grown under rainfed and
irrigated conditions.

Materials and methods

Field study

Two experiments were conducted at the Agricultural Experiment Station,
University of the Virgin Islands, Kingshill, St. Croix, United States Virgin Islands
U.S.V.I. (17° 42' N, 64° 48' W, and 33.5 masl) in 1999 and 2000. Mean temperature was

21

26.1‘
and h
soil 3‘

carbo

State
samp
P ha'
Was a

andr

AGS
bean
Pede
of C

field

addi

One

26.1° C. Seeds were planted on 9 March and harvested on 1 June 1999 and on 6 April
and harvested on 27 June 2000 (stress plots) and on 30 June 2000 (non-stress plots). The
soil at the Experimental Station field site is classified as a Fredensborg loamy, fine
carbonatic, isohyperthermic, shallow, Typic Calciustoll with pH ranging from 7.6 to 8.4.

In 1999, a soil sample from each plot were taken and analyzed by the Michigan
State University Plant Nutrient and Soil Testing Laboratory for N, P, and K. Soil
samples were also analyzed for Zn, Mn, and Cu. As indicated by the soil analysis, 22 kg
P/ha", 5.6 kg Zn/ha", and 10 kg Mn/ha" were applied in 1999 and 2000. No N fertilizer
was applied, since N fixation was also being assessed. Samples from each block (stress
and non-stress) were taken in 2000.

In 1999, applications of insecticide, Sevin 80WP (0.68 kg ai/A) and Diazinon
AG500 (170 g ai/A), were made at one week intervals starting on 26 March to control the
bean leafskeletonizer. One application of fungicide, Benomyl (500 g per 95 L/A) and M-
Pede (Potassium salts of fatty acids) (71 g per 3.8 L/A) was made on 18 April for control
of Cercospora (Cercospora canescens). No insecticides or fungicides were applied to
field plots in 2000.

Water regime

In 1999, 100.8 mm of rainfall were recorded during the growing season. In
addition, plants were irrigated by drip irrigation on 31 days during the growing season for
one hour on each date. Twelve applications were made before the initiation of stress at
21 DAP and 19 were made after stress initiation.

Plant material

22

 

 

habi
nodt
Paln
L'nix

drou

N2 11)
COndL

SCOTE<

Nine common bean genotypes possessing different Type I, II, and 111 growth
habits (Table 1) were included in this study: BAT 477 [nodulating (nod) and non-
nodulating (nn)], DOR 364 [nodulating (nod) and non-nodulating (nn)], XAN 176, ICA
Palmar, 8-42-M-2, SEAS, and PR9603-22, local check (obtained from Dr. James Beaver,
University of Puerto Rico-Mayaguez Campus). BAT 477 (nod) and 8-42-M-2 were the
drought resistant and drought susceptible checks, respectively.

Experimental design

The study utilized a randomized complete block design with four replications,
moisture as the main plot, and genotype as subplot. In 1999, seeds were planted into
four-row plots of 0.5 m row spacing and 2.48 m length. Each row was planted at a
density of 25 seeds and thinned to 23 plants. In 2000, seeds were planted into four-row
plots of 0.5 m row spacing and 2.13 m length and planted at a density of two seeds per
station at 7.62 cm between stations. Seeds were inoculated with a granular form of
Rhizobium etli, which was applied directly within the seed station. Moisture stress was
initiated at the V3 (Nuland and Schwartz, 1989) growth stage or 20 days after planting
(DAP) by cessation of irrigation to the rainfed plots. Control plots were maintained at a
soil moisture content of -30 kPa.

Data collection

Plots were sampled at vegetative (V3), flowering (R2), and podfill stages (R7) for
N2 fixation and weekly. Starting at 23 DAP, plants were sampled weekly for stomatal
conductance, leaf temperature, and leaf transpiration. In 1999, plants were visually
scored for disease on a scale of 0 to 9, with 9 being dead and 0 being no visual symptoms.

23

Days to flower (DF), defined as the number of days when 50% of the plants had one open
flower; days to physiological maturity (DPM), defined as the number of days for 75 to
90% of the pods to lose their green pigmentation; and days to seed fill (DSF=DPM-DF)
were calculated. In 1999, soil moisture was recorded at 44, 51 , and 58 DAP using a
Sentry 200—AP moisture probe (Troxler Electronics Laboratories, Inc.) and in 2000, soil
moisture was determined using the gravimetric method. A hard soil pan prevented soil
moisture recordings below 30 cm, consequently, soil moisture was only recorded at a
depth of 30 cm. At harvest, seed yield was determined at 18% moisture. The MSTAT
micro-computer statistical package (Michigan State University) for agricultural sciences
was used for all data analysis.

Moisture stress indices

Geometric mean (GM) separates genotypes into four categories: (1) those that
yield well both under stress and non-stress environments, (2) those that yield well only ..--
under non-stress, (3) those yielding relatively well under stress, and (4) those yielding
poorly under both stress and non-stress conditions (Fernandez, 1993). The GM is
calculated as: GM = (Ys * Yp)”. Where Y5 = the yield of a given genotype in a stress
environment and Yp = the potential yield of a given genotype in a non-stress
environment. Fernandez (1993) and Schneider et a1. (1997)) observed that the choice of
GM to represent mean productivity is preferred because, when ranking genotypes, GM
better accounts for large differences in performance between stress and non-stress
environments than does the simple arithmetic mean of stress and non-stress yields used
by Rosielle and Harnblin (1981).

24

The drought susceptible index (D81) is reported to estimate drought tolerance. A
value of one is reported to equal average resistance, values lower than one represent
greater than average resistance, and values greater than one indicate susceptibility
(Fischer and Maurer, 1978). The DSI of individual genotypes is calculated as: DSI = [1 -
( Y, / Yp)] / D11, and was the index preferred by Ramirez and Kelly (1998).

The drought intensity index (D11) is calculated as: DII = [l - (Y; / Yp). Where Yg
= mean yield in stress environment and Yp= mean yield in non-stress environment
(Fernandez, 1993). It ranges between 0 and 1 and the larger the value of DII, the more
severe the stress intensity of the test.

The stress tolerance index (STI) has been developed as an alternative to the D81.
Stress tolerance index is reported to measure both stress tolerance and yield potential
Fernandez, 1993). With STI, the higher the value, the greater the stress tolerance and the
higher the yield. Genotypes chosen based upon high STI exhibit high yield potential and
high yield in stress environments (Fernandez, 1993). The STI is calculated as: STI =
[(Ys)(Yp)l/(Yp)2-

Results and discussion

I 999

Soil pH across all plots ranged from 7.6 to 8.0. Soil iron (Fe) content ranged from
3 to 8 ppm with a mean of 5 ppm and percent organic matter ranged from 1.96 to 2.61
with a mean of 2.35. In 1999, soil NO3' ranged from 11 to 39 ppm with a mean of 24
ppm and soil NH4 ranged from 2 to 6 ppm with a mean of 4 ppm.

The genotypes ICA Palmar and PR9603-22 flowered at 34 DAP, while the other

25

 

trans
State
any 5
were
signil
Preci]

moist

genotypes flowered at 38 DAP. However, ICA Palmar never reached physiological
maturity (Table 2). The other genotypes matured over a range of 69 to 75 DAP, and DSF
ranged from 35 to 37 days (Table 2). There were no significant differences among stress
and non-stress treatments (Figure 1) or among genotypes (data not shown) for
transpiration rate. Likewise, leaf temperature measured using a Li-Cor (LI-1600 Steady
State Porometer) porometer was not significant among stress and non-stress treatments on
any sampling dates (Figure 2), however, at 57 DAP using an infrared thermometer, there
were significant genotypic differences with the genotype ICA Palmar having a
significantly higher (P s 0.10) leaf temperature than the other genotypes (Figure 3).
Precipitation was higher than normal (Appendix A), so moisture stress was mild and soil
moisture did not differ between rainfed and control plots except at 58 DAP (Figure 4).
Yield under irrigated conditions ranged from 151 to 1478 kg ha" and for rainfed
conditions from 142 to 1801 kg ha“1 (Table 3). Under irrigated conditions, the genotype
DOR 364 (nod) had a significantly higher (P s 0.01) seed weight than ICA Palmar and 8-
42-M-2 but not significantly higher than the other genotypes (Table 3). In the rainfed
treatment, the genotype PR9603-22 had a significantly higher (P 3 0.001) seed weight
than the genotypes, ICA Palmar, BAT 477 (nn), SEAS, and 8-42-M-2 (Table 3). The
local check, PR9603-22 performed well under both irrigated and rainfed conditions and
the data for PR9603-22 agreed with previous results obtained at the University of Puerto
Rico-Mayaguez indicating that it is a high yielding bean genotype (Personal
communication, Dr. James Beaver). Combined yield of the nine genotypes ranged from

142 to 1508 kg ha", number of pods per m2 from 64 to 519, and pod weight per m2 from

26

 

17 to
had a I‘
BAT
DOR
signif
not fo

had a

 

1C A P
signifi
m3 tha
maturj
detem
genot}
Indete

in Ma

(.CIA]

1988;

rainfeC

17 to 132 grams (Table 3). DOR 364 (nod), XAN 176, and the local check PR9603-22
had a significantly higher (P s 0.01) combined yield than the genotypes ICA Palmar,
BAT 477 (nn), SEAS, and 8-42-M-2 but not significantly higher than BAT 477 (nod) and
DOR 364 (nn). Differences in number of pods per m2 and pod weight per m2 were highly
significant among the genotypes (P s 0.01) and among water treatments (P s 0.05) but
not for genotype x stress. The genotypes DOR 364 (nod), XAN 176, and DOR 364 (nn)
had a significantly (P s 0.01) higher number of harvested pods than BAT 477 (nod & nn),
ICA Palmar, SEAS, and 8-42-M-2 (Table 3). The genotype ICA Palmar had a
significantly lower (P s 0.01) pod weight per m2 and lower number of pods harvested per
m2 than all the genotypes (Table 3), because ICA Palmar did not reach physiological
maturity. ICA Palmar is a Type I bean genotype (Haley et al., 1994) and has a
determinate bush growth habit. Beaver et a1. (1985) found that determinate bean
genotypes tend to have lower yield potential and have less yield stability than
indeterminate bean genotypes, although ICA Palmar performed well in the winter nursery
in Mayaguez, Puerto Rico (Beaver and Kelly, 1994).

There was no significant difference between the resistant check, BAT 477 (nod)
(CIAT, 1984; Gregory, 1989), and the susceptible check , 8-42-M-2 (Acosta-Gallegos,
1988; Manthe, 1994; Yabba, 1997), for yield under irrigated or rainfed treatments and for
combined yield (Table 3). The resistant check, BAT 477 (nod) had a significantly higher
(P s 0.01) number of pods per plot and a significantly higher pod weight per plot than 8-
42-M-2 (Table 3). The susceptible check, 8-42-M-2, produced 64% more seed under
rainfed conditions compared to the irrigated treatment and BAT 477 (nod) produced 27%

27

 

 

more

26110

these

beuei

 

have
hatin
and 1
droug
uuerz
lh€S‘

10pf7

'J)

fang
1eafs
had ;
geno

5USC<

more seeds under rainfed conditions compared to the irrigated conditions. Both
genotypes produced a greater yield under rainfed than irrigated, hence, yield reduction for
these two genotypes were negative. The resistant check, BAT 477 (nod) was one of the
better performers in 1999.

DOR 364 (nn), ICA Palmar, BAT 477 (rm), and SEAS were the only genotypes to
have a yield reduction under rainfed conditions (Table 3) with the genotype ICA Palmar
having the highest percent yield reduction. BAT 477 (rm) and DOR 364 (nn) had a 27
and 17% yield reduction, respectively, in comparison to their nodulating isolines. The
drought susceptible index and the STI selection criteria for assessing plant moisture stress
tolerance, were not calculated for 1999 because yield from five of the nine genotypes in
the stress plots out-yielded plots from the non-stress treatment. However, GM ranked the
top four genotypes as DOR 364 (nod), PR9603-22, XAN 176, and DOR 364 (nn) (Table
3).

Plants were severely infected with common bacterial blight (Xanthomonas
campestris pv. Phaseoli), Cercospora (Cercospora canescens Ellis & G. Martin), bean
leafskeletonizer (near Autoplusia spp), and ozone damage and N-deficiency. ICA Palmar
had a significantly higher (P s 0.01) rating for common bacterial blight than all other
genotypes (Table 4), supporting other work (CIAT, 1979), indicating ICA Palmar’s
susceptibility to common bacterial blight. DOR 364 (nod & nn), PR9603-22, and XAN
176 had the lowest common bacterial blight rating and were the highest yielding lines,
reflecting the significant relationship (R2 = 0.34, P 5 0.001) between common bacterial
blight and yield. Common bacterial blight affects the foliage and pods of beans and is

28

 

consi
1994
desu'.
typic.
contaf

1994

Sevin

and th

 

 

defolh
of all (I
PR96i
There
bacter
Occun
higher
genot:
)‘ieldil
PR96(

Heidi:

considered to be a major problem in most bean production areas of the world (Hall,
1994). During extended periods of warm, humid weather, the disease can be highly
destructive, causing losses in both yield and seed quality. Common bacterial blight
typically develops from (1) planting contaminated seeds, (2) planting seeds in a
contaminated field, and (3) when the climate is consistently hot and wet or humid (Hall,
1994). Because clean seed was planted, common bacterial blight must have been
preexisting in the soil and was brought on by hot and wet weather conditions throughout
the growing season.

Bean leafskeletonizer infected the plants but was controlled with the insecticides
Sevin and Diazinon. Cercospora (C. canescens & C. cruenta) occurs in Latin America
and the southern United States. It can affect all aerial parts of common bean and result in
defoliation. The Cercospora rating for SEAS was significantly higher (P s 0.01) than that
of all other genotypes , and ozone damage was significantly greater (P s 0.05) on _. -
PR9603-22 than on all other genotypes except BAT 477 (nod) and SEAS (Table 4).
There was no significant water x genotype interactions for Cercospora and common
bacterial blight but there was for ozone damage. Significant water x genotype interaction
occurred within the ozone count rating (Table 4). The genotype PR9603-22 had the
highest ozone rating in both irrigated and rainfed treatments (Table 4). Although the
genotype PR9603-22 showed the highest ozone rating, it was still one of the higher
yielding genotypes in the study. As with common bacterial blight, DOR 364 (nod & nn),
PR9603-22, and XAN 176 had the lowest Cercospora rating and were among the highest
yielding lines.

29

The genotype, ICA Palmar produced yields exceeding 2000 kg" ha at the
Agricultural Research Experiment Station in Isabella, Puerto Rico, demonstrating its high
yield potential (Personal Communication, Dr. James Beaver). The failure to mature, the
severe common bacterial blight infestation, the mild infestation of Cercospora, ozone
damage, and feeding damage from the bean leafskeletonizer were significant contributors
to the low yield of ICA Palmar obtained at St. Croix. The failure of ICA Palmar to
mature is inexplicable because there is no difference in photoperiod between Isabella,
Puerto Rico and St. Croix. Further investigation is needed to assess its response to high
pH and soil and air temperature.

Previous work with SEAS (Singh (1995) and Singh et al.(2001) and BAT 477
(nod) in Mexico (Personal Communication with Dr. Jorge Acosta) produced yields that
were appreciably higher than the ones obtained in this study. Nevertheless, the average
yield obtained in 1999 was greater than the average yield obtained in many areas of the
Caribbean and demonstrate the adaptability of common bean to St. Croix and the ability
to produce competitive yields despite insect and disease problems.

2000

In 2000, soil NO,‘ ranged from 20 to 42 ppm with a mean of 30 ppm and soil NH,
, ranged from 4 to 21 ppm with a mean of 9 ppm. In 2000, yield was recorded for eight
genotypes. The genotype ICA Palmar was dropped from yield analysis because of failure
to mature in 1999. There were no significant differences among the genotypes for rainfed
treatment, irrigated treatment, and combined yield (Table 5). Also, there was no
genotype x stress interaction. Irrigated yield ranged from 719 to 1291 kg ha", rainfed

3O

yield -

Com?

lTi-ll‘l

 

 

 

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houet
genot
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s O.h

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PR9.
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X»

yield ranged from 418 to 743 kg ha", and combined yield ranged from 568 to 896 kg ha".
Combined yield was considerably lower than combined yield obtained in 1999. In 2000,
plants showed visible signs of nitrogen deficiency, contributing to the low yield observed.
The genotype PR9603-22 produced moderately good yield under both treatments. Yield
reduction among the genotypes ranged from 15% (SEAS) to 66% (XAN 176) (Table 5).

Number of pods ranged from 102 to 220, and pod weight from 53 to 75 grams
(Table 5). The genotype 8-42-M-2 produced a significantly lower (P s 0.01) number of
pods than all genotypes except the genotypes PR9603-22, BAT 477 (rm), and SEAS,
however pod weight, fifty seed weight, and seeds per pod did not differ among the
genotypes. There were significant differences within irrigated and rainfed treatments in
the number of pods harvested (P s 0.01), pod weight (P 5 0.001), and fifty seed weight (P
s 0.10) but not for number of seeds per pod (Table 5).

Geometric mean was used to assess yield potential, an important factor since a
genotype might be low yielding under sufficient moisture conditions, but have minimal
yield reduction under stress. The GM ranked DOR 364 (nn), PR9603-22, SEAS, and
DOR 364 (nod) in that order, as having the highest yield potential (Table 5). The
genotype XAN 176 had the highest D81 and SEAS had the lowest (Table 5). According
to this system, the resistant genotypes in order from most to least resistance were SEAS,
PR9603-22, DOR 364 (rm), and BAT 477 (nod). The genotype PR9603-22, DOR 364
(nod), and DOR 364 (nn) were among the top four genotypes selected by GM in 1999
and in 2000. The susceptible genotypes in order from most to least susceptible were
XAN 176, BAT 477 (nn), DOR 364 (nod), and 8-42-M-2.

31

Stress tolerance index ranged from 0.30 to 0.77 with the genotype DOR 364 (nn)
having the highest value indicating the greatest resistance and highest yield potential and
the genotype 8-42-M-2 having the lowest value indicating susceptibility and low yield
potential (Table 5). According to the STI, the genotypes having the greatest resistance
and highest yield potential were DOR 364 (nn), PR9603 -22, SEAS, and DOR 364 (nod),
similar to results obtained for GM. Stress tolerance index and D81 agreed on the
genotypes that would be assessed as resistant or susceptible, but the order within
categories differed.

The GM, D81, and ST] were each analyzed to determine their degree of
correlation with yield under stress conditions, yield under non-stress conditions, and
combined yield of the two moisture treatments. The correlation of GM and STI with
yield under stress and combined yield was positive and highly significant, ranging from
0.79* to 0.94“” (Table 6). As expected, the DS1 was inversely correlated with yield __--
under stress (-0.83**) (Table 6). The GM and STI were more accurate than the D81 in
selecting desirable genotypes based upon yield performance at the Agricultural
Experiment Station in 2000. Our results are similar to results obtained by Schneider et al.
(1997) who concluded that GM was the single strongest indicator of yield performance
under stress and non-stress. They suggested that the most effective breeding strategy to
improve drought resistance in common bean should first involve selection based on the
GM, followed by selection based on yield under stress.

Effect of pH on yield of common bean

The high soil pH (7 .6 to 8.0) at the Agricultural Experiment Station caused

32

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concern about its potential effect on seedling germination rate and on yield since common
bean grows best at a pH range of 6.0 to 7.2 (Hall, 1994). In 1999, there was a
germination rate of 90% and in 2000 of approximately 85%. In 2000, due to limited
water pressure at the Agricultural Experiment Station, germination on the South side of
the trial (approximately 3 plots from each replication and treatment) was sporadic and
those plots had to be replanted. Mean seed yield for 1999 was 1100 kg ha" (excluding
the genotype ICA Palmar, 994 kg ha" including ICA Palmar) and 803 kg ha" for 2000,
excluding the genotype ICA Palmar. These yield are comparable to results obtained in
Trinidad (1100 kg ha", Gonsalvez, 1975), but low compared to reports from other bean
growing areas in the Caribbean such as Puerto Rico (1988; 2100 kg ha", Badillo-
Feliciano, 1977), the Dominican Republic (1700 kg ha", Beaver et al., 1988), Jamaica
(1300 kg ha", Malcolm and Salmon, 1979), and Cuba (1362 kg ha", Isasi and Busto,
1984). Results from the two years of this study showed that seedling germination and
growth of common bean is possible on a high pH soil at the Agricultural Experiment
Station and that yields, while low, are still competitive with a few other bean producing
areas of the Caribbean.

The most prominent nutritional disorders of crop plants grown in soils with high
pH are iron, zinc, and manganese deficiencies (Schinas and Rowell, 1977). Plant species
that are mainly affected include apple (Malus domestica Borkh.), peaches (Prunus
persica (L) Batsch.), grape (Vitis vinifera L), peanut (Arachis hypogaea L), soybean
(Glycine max (L) Men), sorghum (Sorghum bicolor L), and upland rice (0022a sativa
L.) (Marschner, 1997). It is the major problem in sorghum and soybean production in the

33

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SeVe
bean
hon
youn
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(1001
by C1
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line,

and (

Great Plains of the United States (Clark, 1988). Iron deficiency chlorosis is frequently
observed in beans grown on high pH calcareous soils where there is a decrease in the iron
solubility due to the formation of insoluble ferric oxides (Lindsay and Schwab, 1982).
Severe iron deficiency chlorosis can cause significant seed yield reduction in common
bean (Zaiter et al., 1992). Reports indicated that common beans have a high sensitivity to
iron deficiency (Clark, 1988). Symptoms of iron deficiency in common bean appear in
young leaves, which become pale yellow, almost white, while the veins remain green,
fully expanded leaves curve downward, and leaf tips may wilt (Hall, 1994). Similar
symptoms were visually observed in the field trials in 1999.

Nutritional and pathological problems

In 1999, 52% (r2 = 0.52, P s 0.01) of the yield under irrigated conditions was
explained by plant response to CBB (r = -0.35, P s 0.05) and potassium (r = -0.14, P g
0.001) while 42% (r2 = 0.42, P s 0.01) of the yield under stress conditions was explained
by CBB (r = -0.32, P s 0.01) and ozone damage (r = 0.23, P s 0.05). Field plots were not
analyzed for iron in 1999, but an iron test was performed on soil samples in 2000. Iron
concentration at the UVI Agricultural experiment Station ranged from 4 to 8 ppm (0.004
to 0.008 mg Fe kg" of soil) which is low, since mineral soils have, on average, a total iron
content of approximately 2% (20 mg Fe kg" of soil) (Marschner, 1997). The data and
visual symptoms suggest that plants suffered from iron deficiency in 1999 and 2000.
Furthermore, plants displayed visual symptoms of N deficiency, especially in 2000;
Macrophomina phaseolina and Rhizoctonia solani in 2000, and common bacterial blight

and Cercospora in 1999 and 2000.

34

Conclusion

Days to flower ranged from 34 to 38 DAP and days to maturity ranged from 69 to
75 DAP. Yield at the University of the Virgin Islands Agricultural Experiment Station
for the nine genotypes in this trial ranged from 142 to 1508 kg ha" in 1999, and from 568
to 896 kg ha" in 2000. Yields were severely reduced by a combination of factors such as
high pH, nitrogen deficiency, common bacterial blight, Cercospora, ozone damage, and
bean leafskeletonizer. The genotypes ICA Palmar and SEAS had the greatest yield
reduction due to these diseases, each producing less than 700 kg ha". However, XAN
176, DOR 364 (nod), and the line PR9603-22 produced yields exceeding 1300 kg ha".
These lines exhibited a higher tolerance to moisture stress and showed that relatively high
yields are possible in St. Croix despite high soil pH, shallow alkaline soils, and insect and
disease problems. Results are important because Crucians consume large quantities of
common bean and the island has the potential for common bean production, although
none is grown on the island. Future work should investigate bean pathogens and

nutritional disorders.

35

ACO?

AC 0 .‘

Badi'.

Beat

Beau

 

 

 

Clark.

Literature cited

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genotypes with enhanced drought tolerance and biological nitrogen fixation.
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Adams, M.W. 1996. An historical perspective on significant accomplishments in dry
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Beaver, J .S., and J .D. Kelly. 1994. Comparison of selection methods for dry bean
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37

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“hi

\\hi

“hi

Yab

Zai‘

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39

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Table 2. Days to flower (DF), days to physiological maturity (DPM), and days to seed
fill (DSF) of nine common bean (Phaseolus vulgaris L.) genotypes grown at the

Agricultural Experiment Station at the University of the Virgin Islands-St. Croix

 

 

 

Campus, U.S.V.I.

Genotypes DF DPM TDSF
BAT 477 (nod) 38 75 37
PR9603-22 34 69 35
DOR 364 (nn) 38 73 35
ICA Palmar 34 I --
XAN 176 38 73 35
BAT 477 (nn) 38 75 37
SEAS 38 75 37
8-42-M-2 38 75 37
DOR 364 (nod) 38 73 35

'l DSF = DPM - DF

I The genotype ICA Palmar did not reach physiological maturity.

41

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Table 4. Common bacterial blight (CBB) (Xanthomonas campestris pv. phaseoli),

Cercospora (C ercospora canescens), and ozone rating of nine bean (Phaseolus

vulgaris L.) genotypes grown at the Agricultural Experiment Station at the

University of the Virgin Islands-St. Croix Campus, U.S.V.I. 1999. Scale 0 to 9

with O = no visual symptoms and 9 = death. N = 8 and 4 (rainfed and irrigated

 

 

 

treatments).

Genotypes CBB Cercospora Ozone IOzone §Ozone
BAT 477 (nod) 4.75 b** 6.20 b** 3.63 ab“ 4.50 flabc+ 2.75 d
PR9603-22 2.36 c 2.75 cde 4.88 a 5.00 a 4.75 ab
DOR 364 (nn) 2.19 c 2.31 de 3.38 b 2.25 d 4.50 abc
ICA Palmar 8.25 a 3.50 cd 2.88 b 2.50 d 3.25 bcd
XAN 176 2.50 c 2.31 de 2.44 b 2.63 d 2.25 d
BAT 477 (nn) 3.63 be 4.44 c 3.38 ab 3.75 abcd 3.00 cd
SEAS 4.38 b 8.75 a 3.88 ab 4.75 ab 3.00 cd
8-42-M-2 3.75 bc 3.13 cde 3.50 b 4.00 abcd 3.00 cd
DOR 364 (nod) 1.94 c 1.38 e 2.50 b 2.50 d 2.50 d
Mean 3.75 3.68 3.38 3.54 3.22

1: Indicates ozone count under irrigated conditions.

Indicates ozone count under rainfed conditions.

irrigated and rainfed conditions).

Statistical significance of stress x genotype interaction (ozone count under

**,"‘ , +. Different letters indicates significant difference among means within a

column at P s 0.01. 0.05 and 0.10, respectively, according to DMRT.

43

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44

Table 6. Correlations of yield under stress, yield under non-stress, and combined yield
for stress and non-stress treatments to geometric mean (GM), drought
susceptibility index (DSI), and stress tolerance index (STI). Data from eight
genotypes of common bean (Phaseolus vulgaris L.) grown at the Agricultural

Experiment Station at the University of the Virgin Islands-St. Croix Campus,

 

 

U.S.V.I. 2000.
2000
GM DSI STI
Stress Yield 0793* -0.834** 0.821 *
Non-stress Yield 0.510 0.626" 0.462
Combined Yield 0.938*** -0.007 0.916"

 

+, *, **, ***. Indicates significance at P s 0.10, 005,001, and 0.001, respectively.

45

160 - E Stress

I Nonstress

  

120 -

80-

40-

Transpiration rate (g cm-2 s-l)

 

Growth stages

Figure 1. Transpiration rate (means :1: SE, n = 36) of nine genotypes of common
bean grown under irrigated and rainfed moisture conditions at the Agricultural
Experiment Station at the University of the Virgin Islands, 1999. Vertical bars indicate

standard error of the mean.

46

Stress
33 .
I Nonstress

Leaf temperature (0C)

 

 

V3 V3/4 R1 R4/5 R6/7
Growth stages

Figure 2. Leaf temperature (means i SE, n = 36) of nine common bean
genotypes using a LiCor (L1 1600 Steady State) porometer grown under irrigated
and rainfed moisture conditions at the Agricultural Experiment Station at the
University of the Virgin Islands, 1999. Vertical bars indicate standard error of

the mean.

47

35.

Temperature (°C)

 

 

PR9603-22
BAT477(nn) j
SEAS
8-42-M-2

ICA Palmer '9; .. ,3“, . _ j“;-
DOR 364 (nod)

; ii;
4 A;
.1"?
A
I:
:
v
v
e
n
a:
O
G

BAT 477 (nod)

Figure 3. Leaf temperature (means 2 SE, n = 8) of nine common bean genotypes
taken with an infra-red thermometer at 57 DAP and grown under irrigated and
rainfed moisture conditions at the Agricultural Experiment Station at the

University of the Virgin Islands, 1999. Vertical bars indicate standard error of the

mean at P S 0.10.

48

0.8 -

D Stress

I Nonstress

Probe counts

 

 

Figure 4. Sentry probe counts (means :t SE, n = 36) of nine common bean
genotypes taken at a depth of 30.5 cm and grown under irrigated and rainfed
moisture conditions at the Agricultural Experiment Station at the University of
the Virgin Islands, 1999. Vertical bars indicate standard error of the mean at

R6/7 at P S 0.10.

49

Chapter 2
Root length, shoot weight, and root length density in common bean (Phaseolus
vulgaris L.).
Abstract
One characteristic that may contribute to drought resistance in common bean is
root mass. The objective of this study was to determine if drought resistant genotypes
have differing root growth. Plants were grown in half-strength Hoagland’s nutrient
solution (control treatment) or half-strength Hoagland’s nutrient solution + 10"" M
abscisic acid (ABA treatment) in an environmentally controlled growth chamber. In
another study, plants were grown in polyvinyl chloride (PVC) tubes in a glasshouse for
40 days. The ABA treatment increased total root length (TRL) and root length among
root width classes. The susceptible check, 8-42-M-2 produced a greater portion of fine
roots and a greater TRL than the resistant check, BAT 477 [nodulating (nod)]. In the
PVC study, water deficit significantly reduced root width classes at all depths except at a
depth of 30.6 - 45.7 cm and reduced TRL by approximately 75, 38, and 38% at depths of
0 - 15.2, 15.3 - 30.5, and 0 - 92 cm, respectively. Root length density was low ranging
from 0.01 - 0.49 cm cm ‘3. Fine roots made the largest contribution to total root length in
both stressed and nonstressed treatments. Growth pouch and PVC studies identified
XAN 176, SEAS, and 8-42-M-2 as having high TRL, suggesting that growth pouches

may provide a viable method for assessing root growth.

50

Introduction

Identifying and understanding the mechanisms of drought tolerance in common
bean (Phaseolus vulgaris L.) have been major goals of plant physiologists and breeders.
Several mechanisms which permit common bean to achieve economic yields under
drought environments have been proposed, including rooting depth (Sponchiado et al.,
1989; White et al., 1990), ability to maintain stomatal opening at low levels of leaf water
potential (Bates and Hall, 1981; Peng et al., 1991), high osmotic adjustment (Salih et al.,
1999), stomatal conductance, and photosynthesis (Hamdani et al., 1991; Manthe, 1994).
It is accepted that abscisic acid (ABA) acts as a stress hormone in plant systems, and the
relationship between ABA levels and plant water status have been investigated
extensively (Pierce and Raschke, 1981; Hartung and Davies, 1990). ABA may also play
a role of importance in temperature stresses which affect plant water relations (Radin and
Hendrix, 1986; Morgan, 1990).

Root characters are undoubtedly important in edaphic adaptation. Several
researchers have shown that drought tolerance in common bean is related to depth of
rooting (Sponchiado et al., 1989; White et al., 1990). Soil exploration by roots is
associated with nutrient acquisition, especially in the case of immobile nutrients such as
. phosphorus (Lynch and van Beem, 1993; Yan et al., 1995a). Genetic differences have
been reported in common bean for root biomass and root to shoot ratio (Fawole et al.,
1982; Stofella et al., 1979a), and for root biomass distribution among distinct root types
(Stofella et al., 1979b). In addition to parameters related to root size and growth, root
architecture may be important for mining minerals, nutrients, and water from the soil

51

(Lynch and van Beem, 1993). Fitter (1991) developed topological indices to quantify
root architecture in two-dimensions, ranging from a hen'ingbone structure at one extreme
to a highly branched, dichotomous structure at the other extreme (Fitter, 1991). Based on
comparisons of ecologically distinct species, Fitter (1991) has proposed that root
architecture may influence the efficiency of mineral, nutrient, and water acquisition from
the soil.

Research on bean root growth has been conducted in hydroponics systems
(Gabelman et al., 1986; Checkai et al., 1987), in field settings (Yan et al., 1995b), a spilt
root system (Snapp and Lynch, 1996), and pots of different sizes (Lynch and van Beem,
1993; Yan et al., 1995a). Still, the understanding of the effects of moisture deficits on
bean root growth remains at a rudimentary level. Yabba (1997) using a modification of
the procedure used by Asady and Smucker (1989) observed root grth to a depth of
0.76 m in common bean grown for 40 days in polyvinyl chloride tubes.

Quantification of root growth and distribution is necessary to understand plant-
soil interactions. However, root research has been hampered by inadequate, time-
consuming methods (Persson, 1990). Advances in nondestructive methods of quantifying
roots include nuclear magnetic resonance imaging (Rogers and Bottomley, 1987) and
minirhizotron technologies (Taylor, 1987). Despite these efforts, there is a need for better
knowledge and understanding of root grth and function as related to soil water status
(Wraith and Wright, 1998). Hence, the objective of this study was to investigate the

effects of water deficit and abscisic acid (ABA) on root length and root length density.

52

Materials and methods

Growth chamber study:

Two experiments were conducted in an environmentally controlled growth
chamber to evaluate common bean seedling root growth: a control treatment in which
plants were given only half-strength Hoagland’s (Hoagland and Arnon, 1950) nutrient
solution (control) and an abscisic acid (ABA) treatment consisting of half-strength
Hoagland’s nutrient solution + 10‘6M ABA [cis-trans, i ABA, Sigma]. A 23/200C
day/night temperature and a 15 h photoperiod were used for both experiments.
Photosynthetically active radiation (PAR) was measured as 876 umol m'23" (control) and
913 umol mas" (ABA) at the top of the of the plant canopy using a Decagon Sunfleck
Ceptometer (Pullman, Wash.) Eight common bean genotypes with Type II and III
growth habits were selected for study: BAT 477 (nod), PR9603-22, DOR 364 (nn) XAN
176, BAT 477 (nn), SEAS, 8-42-M-2, and DOR 364 (nod). The study utilized a
randomized complete block design with four replications, days after transplant (14, 21 ,
and 28 DAT) as the main plot, and genotype as subplot. Uniform sized seeds were
selected and soaked in a l umol CaSO4 solution for one hour before germination. Seeds
were germinated 5 days prior to the initiation of the experiment. Seedlings were
transplanted, at one seed per pouch, to a specially designed growth pouch measuring 25.4
cm x 35.6 cm, an adaptation of a procedure used by McMichael et al. (1985), Merhaut et
a1. (1989), and Yabba (1997). All pouches were given 50 ml of half-strength Hoagland’s
nutrient solution (control treatment) or half-strength Hoagland’s nutrient solution + ABA
and adjusted to a pH of 6.14. Pouches were then stapled to a black cardboard and placed

53

upright in a specially designed holder with 2.54 cm between pouches. Seedlings were
covered with a clear plastic covering for two days. Plants were given nine 50 ml
applications of half-strength Hoagland’s nutrient solution or half-strength Hoagland’s
nutrient solution + ABA from the sixth to the twenty-eighth DAT when the experiment
was terminated. Plants were sampled at 14, 21, and 28 DAT. Fresh weights were taken
for roots, stem, and leaves. Fresh roots were placed in a whirlpack bag and stored in 15%
(v/v) methanol solution at 4°C. Leaves and stem were oven dried for 48 h at 60°C,
weighed and discarded. Roots were prepared for root imaging according to the WinRhizo
root imaging program (WinRhizo, Regent Instruments Inc.).

Glasshouse study

Plants were grown in polyvinyl chloride tubes (PVC) for 40 days in a glasshouse
at Michigan State University, in East Lansing, MI. The temperature regime was 27°C i
2°C and the light intensity was 1421 uE m'zs'l with a 15 h photoperiod. Nine common
bean genotypes with Type I, II, and III growth habits were grown: BAT 477 (nod),
PR9603-22, DOR 364 (nn), ICA Palmer, XAN 176, BAT 477 (nn), SEAS, 8-42-M-2, and
DOR 364 (nod). The experimental design was a split plot with water (stressed and non-
stressed) as the main plot, genotypes as the subplot, and three replications. The PVC
tubes were 0.92 m in length with a diameter of 30.5 cm. To determine root growth at
different depths each PVC tube was cut into six 16.6 cm sections. The six individual
sections were taped to produce one continuous tube. The bottom section was filled with
silica sand. The remainder of the PVC tube was filled with a Metea loam (Loamy,
mixed, mesic, Arenic Hapludalfs) that had been sieved through a 2 mm mesh wire and

54

packed to a bulk density of 1.37 g/cm3. Five seeds per PVC tube were planted on 7
August, 2000 and thinned to one plant per PVC tube at 14 days after planting (DAP).
Stress was initiated at 14 DAP by cessation of water to plants in the stress treatment.
Plants were given 18 L of water during the growing period (4 L before stress initiation
and 14 L after stress initiation). Plants were sampled at R2 growth stage (40 DAP). Stem,
leaf, and reproductive parts were weighed and dried at 60°C for 48 h, reweighed and then
ground through a 1 mm screen Udy Cyclone Sample Mill (Udy Corporation, Fort Collins,
CO.) for determination of total nitrogen. Roots were extracted from each section by
sieving the soil through a 2 mm mesh wire. Fresh roots were placed in a whirlpack bag
and stored in 15% (v/v) methanol solution at 4°C. Roots were prepared for root imaging
according to the WinRhizo root imaging program (WinRhizo, Regent Instruments Inc.).

Root Quantification

The WinRhizo image analysis software was used to analyze the image root files
acquired. Total area (image area), total volume, and average root diameter were
calculated simultaneously by a procedure outlined by Tennant (1975). Roots were
divided into 10 classes, based upon root diameter. The classes were: class 1 (0 - 0.5 mm),
class 2 (0.51 - 1.0 mm), class 3 (1.01 - 1.5 mm), class 4 (1.51 - 2.0 mm), class 5 (2.01 -
2.5 mm), class 6 (2.51 - 3.0 mm), class 7 (3.01 - 3.5 mm), class 8 (3.51 - 4.0 mm), class 9
(4.01 - 4.5 mm), and class 10 (> 4.5 mm). In addition, root morphology measurements
(length, volume, surface area) were calculated simultaneously with WinRhizo Regent’s
non-statistical method which estimates length distribution among specified root diameter
ranges (WinRhizo User Manual, regent Instruments, Inc.). After scanning, roots were

55

oven dried at 60°C for 3 (1, dry weights were recorded and then discarded. The MSTAT
micro-computer statistical package (Michigan State University) for agricultural sciences
was used for all data analysis.

Results and discussions

Root parameters: Growth chamber study.

Root length was significantly higher in the ABA than in the control treatment for
total root length (TRL) at 14 and 21 DAT and for all root classes except root class 9 at 21
DAT (Table 1). At 14 DAT, only root class 8 had a significant difference (P s 0.01)
between ABA and control treatments. At 28 DAT, significant differences existed
between the two treatments for TRL and for root classes 2, 3, 7, and 9 (Table 1). ABA
increased TRL by more than 50% at 21 and 28DAT. Results support previous work
(Yabba, 1997) indicating ABA stimulation of root growth in common bean although that
study concluded at 14 DAT.

There were no significant difference among genotypes at 14 DAT between
treatments nor was there a genotype x experiment interaction (Table 2). At 21 DAT, the
genotype XAN 176 had a significantly higher (P s 0.05) TRL than all genotypes in the
control treatment except SEAS and the genotype SEAS had a significantly higher TRL
than all the genotypes in the ABA treatment except PR9603-22, DOR 364 (rm), and 8-42-
M-2 (Table 2). At 21 DAT, the genotype SEAS grown in the ABA treatment had a
significantly higher (P s 0.10) TRL than all genotypes except PR9603-22, DOR 364 (rm),
and 8-42-M-2 in the ABA treatment (Table 2). There were no significant differences
between BAT 477 (nod) and DOR 364 (nod) and their respective isolines at 21 DAT with

S6

regard to TRL in ABA or control treatments. However, DOR 364 (nn) (ABA treatment)
had a significantly (P s 0.10) higher TRL than both DOR 364 (rm) and DOR 364 (nod) in
the control treatment (Table 2).

At 28 DAT, there were no significant differences among the genotypes in the
control treatment (Table 2). In the ABA treatment, the genotype 8-42-M-2 had a
significantly higher (P s 0.01) TRL than all genotypes except DOR 364 (rm) and a
significantly higher (P s 0.01) TRL than all genotypes in the control treatment (Table 2).
There was no significant difference between BAT 477 (nod) and its isoline BAT 477 (nn)
in the control or ABA treatments at 28 DAT but DOR 364 (nn) had a significantly higher
TRL than its isoline DOR 364 (nod) in the ABA treatment and than DOR 364 (nn) in the
control treatment at 28 DAT (Table 2).

The ABA treatment increased TRL on all sampling dates and increased the
production of finer roots with greater than 99% of the roots occurring in root classes 1
and 2 (Table 1). This is significant because such an occurrence during a moisture deficit
would increase the root absorptive surface area, thereby permitting the plant to obtain
more soil moisture (Yabba, 1997). Roots generally explore and contact only 1 - 2% of
the soil volume (Tesar, 1988), therefore an increase in root length increases the plant’s
ability to mine more water and nutrients. Since many root functions, such as water and
ion uptake, are more closely related to root length than root volume (Waisel et al., 1996),
the greater change in root length observed with the ABA treatment implies that plants
growing in an ABA rich medium have a greater ability to obtain such resources. These
results agree with other work indicating that ABA stimulates root growth (Yabba, 1997;

57

Sharp et al., 1993; Robertson et al., 1990; Creelman et al., 1990).

When ABA is applied to roots, the volume of water flow through the root is often
increased, thereby increasing nutrient flow to the root (Cornish and Radin, 1990; Hegazi
et al., 1999), hence resulting in more root growth. This is obviously an important
attribute during water stress because it can improve the plant’s water balance. This
increased transport has been ascribed to either decreased hydraulic resistance in the roots
(Glinka and Reinhold, 1971) or enhanced ion transport that increases the osmotic forces
driving water flow through the root (Karmoker and van Steveninck, 1978).

At 14 DAT plants in both treatment may have been conducting very little
photosynthesis and root growth may have been supported by photosynthates supplied by
the cotyledons. If roots in both treatments were subjected to such a phenomenon, similar
root growth among similar genotypes would be expected and the data at 14 DAT (Table
2) do reflect this.

From 21 DAT to 28 DAT plants may have started conducting photosynthesis and
were producing more root hairs and more lateral roots. Waisel et al. (1996) has reported
that root hairs and root laterals may be induced in an ABA liquid medium by increasing
its oxygen content. Our study was conducted in an aqueous medium but we did not have
an elevated oxygen content. Waisel et al. (1996) reported that one of the most obvious
effects of ABA on Brassicaceae root growth was an increase in the number of lateral
roots and an increase in both the number and length of the root hairs. However, it was
not clear whether the enhancing effects of ABA on lateral root initiation and root hair
formation resulted directly from inhibitory effects of ABA on the extension of the apical

58

root zone (Biddington and Dearman, 1982).

At 21 and 28 DAT, the ABA treatment of 8-42-M-2 produced greater root length
than the ABA treatment for BAT 477 (nod), BAT 477 (rm), and DOR 364 (nod). These
results are surprising since 8-42-M-2 is the drought susceptible check and BAT 477 (nod)
the resistant check. We had postulated that drought resistant genotypes have a greater
mass of fine roots than drought susceptible genotypes and that this might be one
characteristic contributing to the drought resistance of BAT 477 (nod).

Root parameters: Glasshouse.

Water deficit significantly reduced common bean TRL in various root classes at
all depths except at a depth of 30.6 - 45.7 cm (Table 3a and b). Total RL for the non-
stress treatment at all depths was numerically higher than the stress treatment (Table 3a
and b) and significantly higher in the top 30.5 cm (Table 3a). At all depths, the percent of
roots less than or equal to 1.0 mm in diameter was 95% of the TRL for both stressed and
nonstressed plants and at some depths it approached 100% of the TRL (Table 3a and b).
There were no significant genotypic (stressed and nonstressed combined) differences at
any depth except at 45.8 - 61 cm (Table 4). At the 45.8 - 61 cm depth, the genotype
SEAS had a significantly higher TRL (P s 0.10) than the genotypes BAT 477 (nod),
PR9603-22, DOR 364 (rm), and DOR 364 (nod) but not significantly higher than the
other genotypes (Table 4). Each root width class was analyzed at each soil depth for
genotypes (stress and nonstress RL combined), water, genotype x water interaction, stress

RL, and nonstress RL (Tables 5 and 6). Among the genotypes, a cluster of significance

59

was observed for root width class 3 at a depth ofO - 15.2, 15.3 - 30.5, 30.6 - 45.7, and
45 .8 - 61 cm and another cluster at a depth of 45.8 - 61 cm (root width classes 1, 2, 3, 4,
S, 6, and 10) (Table 5). The data for significant differences among water treatments
(Table 5) are presented in tables 3a and b. Significant genotype x water interaction was
observed only at a depth of 0 - 15.2 cm (P s 0.10) in root width class 4 and at a depth of
45.8 - 61 cm (P s 0.10) in root class 5 (Table 5). In the stress treatment three clusters of
significance were observed: TRL (root width classes 1, 2, 3, 4, 5, and 10), at depth 15.3 -
30.5 cm (root width classes 1, 2, 3, 4, and 10), and at depth 45.8 - 61 cm (root width
classes 1, 2, 3, 4, S, 6, and 10) (Table 6). In the nonstress treatment significant difference
was only observed at a depth of 0 - 15.2 cm (root width classes 3 (P s 0.05) and 4 (P s
0.05)) and depth 45.8 61 cm (root width classes 3 (P s 0.10) and 4 (P s 0.10)) (Table 6).
The data for all clusters are presented in tables 7 - 11. Thus, the genotypic differences
largely result from genotypic differences under stress. -.. ._
The first genotypic cluster consisted of root width classes 3, 4, and 10 at a depth
of 1 - 15.3 cm and root width class 3 at depths 15.4 - 30.5 and 30.6 - 45.7 cm (Table 7)
and the second cluster consisted of root width classes 1, 2, 3, 4, 5, 6, and 10 at depth 45.8
- 61 (Table 8). The genotype 8-42-M-2 had a significantly higher (P s 0.05) class 3 RL
than all genotypes except ICA Palmar and XAN 176 at depth 0 - 15.2 cm and the
genotype XAN 176 had a significantly higher (P s 0.05) class 4 RL than all other
genotypes except ICA Palmar at depth 0 - 15.2 cm (Table 7). BAT 477 (nod) had a
significantly greater (P 50.10) class 10 RL at depth 0 - 15.2 cm than PR9603-22, SEAS,
8-42-M-2, and DOR 364 (nod) (Table 7). The genotype XAN 176 had a significantly

60

greater (P s 0.10) class 3 RL at depth 15.3 - 30.5 cm than all genotypes but not
significantly greater than ICA Palmar, BAT 477 (rm), and 8-42-M-2. BAT 477 (nod) had
a significantly higher (P s 0.10) class 3 RL at depth 30.6 - 45.7 cm than PR9603-22,
DOR 364 (rm), and DOR 364 (nod) (Table 7).

At depth 45.8 - 61 cm, the genotype XAN 176 had one of the highest root lengths
at each of the classes (Table 8). XAN 176 was significantly higher than BAT 477 (nod),
PR9603-22, and DOR 364 (nn) for all root width classes except root width class 6. The
genotype 8-42-M-2 (susceptible check) was higher than BAT 477 (nod) only for root
width class 1. The genotypes BAT 477 (nod), BAT 477 (nn), DOR 364 (nod), and DOR
364 (nn) did not differ significantly for root width classes 1 to 6 and 10 at depth 45.8 - 61
cm (Table 8).

In the first cluster among the stress treatment (Table 6) across all depths, the
genotype SEAS had one of the highest TRL’s in all the root width classes analyzed, as
did ICA Palmar, XAN 176, and 8-42-M-2 (Table 9). DOR 364 (nn) consistently had one
of the lowest TRL’s across root width classes. When comparing BAT 477 (nod), BAT
477 (nn), DOR 364 (nod), and DOR 364 (nn) the only difference was when TRL of BAT
477 (nn) exceeded that of DOR 364 (nn) for root width classes 3 and 10 (Table 9).

In the second cluster in the stress treatment which consisted of five root width
classes at depth 15.3 - 30.5 cm, the genotype XAN 176 had one of the greatest RL’s in
root width classes 1 to 4 and 10, as did 8-42-M-2 (Table 10). In, root width class 1, again
DOR 364 (nn) had one of the lowest TRL’s for root width classes 1 to 4 and 10 (Table
10).

61

In the third cluster which consisted of root width classes 1 to 6 and 10 at depth
45.8 - 61 cm, SEAS had one of the greatest RL’s in all the root width classes analyzed
(Table 11). DOR 364 (nn) had one of the lowest RL’s of all root width classes, although
it did not differ significantly from BAT 477 (nod), BAT 477 (rm), and DOR 364 (nod)
(Table 11).

These results indicate that root width classes 1, 2 and 3 (0 - 0.50, 0.51 - 1.0, and
1.01 - 1.50 mm, respectively) contributed the most to TRL among genotypes and
treatments. It is also evident that some genotypes produce a greater portion of these root
width classes than others indicating that fine root may be a meaningful trait that plant
breeders can use in their efforts to breed for drought resistance in common bean.

Root dry weight (RDW), RL, root surface area (RSA), root volume (RV), and root
length density (RLD) parameters were significantly lower in the stressed treatment at 0 -
15.2 and 15.3 - 30.5 cm depths (Table 12). Root diameter was only significant at 15.3 -
30.5 and 76.3 - 92 cm depths with the nonstress treatment having a higher root diameter
(Table 12). Root length density, an index of water uptake capacity ranged from 0.01 -
0.49 cm cm’3 and was significantly lower in the stress treatment at the 0 - 30.5 cm depth
(Table 12). There was no significant difference in RLD in the 30.6 - 76.2 cm portion of
the column, however RLD of the nonstressed treatment at all depths was numerically
higher than the stressed treatment (Table 12). There were no significant differences
between stress and nonstress treatment among any of the root parameters at a depth of
30.6 to 76.2 cm, however RDW and RD was significantly higher in the nonstress
treatments at depth 76.3 to 92 cm(Table 12).

62

There were significant genotypic differences for combined stress and nonstress
RLD only at depths 45.8 - 61 cm (combined stress and nonstress RLD) and 15.3 - 30.5
cm (stress treatment) (Table 13). At depth 15.3 - 30.5 cm in the stress treatment, the
genotype XAN 176 had a significantly higher (P s 0.01) RLD than all the genotypes
except BAT 477 (rm) and 8-42-M-2. At depth 45.8 - 61 cm, the combined stress and
nonstress RLD of XAN 176 was significantly higher (P s 0.10) than BAT 477 (nod),
DOR 364 (rm), and DOR 364 (nod) but not significantly higher than the other genotypes
(Table 13). There were no significant difference in RLD between the two non-
nodulating line (BAT 477 (nod) and DOR 364 (nod)) and their respective isolines at any
of the depths (Table 13). There was no significant difference between the resistant check
(BAT 477 (nod)) and the susceptible check (8-42-M-2) at depth 15.3 - 30.5 cm, of the
stress treatment, but there was at depth 45.8 - 61 cm for combined RLD with 8-42-M-2
having a higher RLD (Table 13).

Results indicated that fine roots (3 1.0 mm diameter) made the largest
contribution to total root length in both stressed and nonstressed treatments. The data
suggest that water absorption may be more associated with fine than large roots. Water
stress reduced TRL by approximately 75, 38, and 38%, respectively, at depths of 0 - 15,
15.1 - 30.5, and 0 - 92 cm.. Results support work by others indicating that the
distribution of roots in a soil profile is largely a function of depth (Box, 1996) and work
indicating that rooting depth and root system development are closely related to soil
moisture content (Asady and Smucker, 1989; Waisel et al., 1996; Manschadi et al., 1998).
In a dry soil, root distribution and downward penetration of roots are restricted due to an

'63

increase in soil strength (Gerard et al., 1982; Jones et al., 1991). If water stress is
moderate to severe , downward root growth will be slowed (Ehlers et al., 1983; Bennie
and Botha, 1986; Manschadi et al., 1998) resulting in a shallower rooting depth. If water
stress persists long enough to prevent root growth from extending into the deeper soil
layers, the total root system will be restricted to the upper part of the profile (Chaudhary
et al., 1985). My results showed that stress had an effect on the rooting depth (lessening
RL to the lower soil profile) and root length (decreasinijL among all root width classes
and at all soil depths) and are consistent with similar findings in faba-bean (Viciafaba L.)
(Manschadi et al., 1998; Heeraman and Juma, 1993) and barley (Hordeum vulgare L.)
(Manschadi et al., 1998).

Since root size and morphology are important in the efficient uptake of nutrients
and minerals (Sullivan et al., 2000), detecting differences in root growth patterns and
length between common bean genotypes may offer unique selection criteria for drought - _.
tolerance. The genotype SEAS produced the greatest combined RL at a depth of 45.8 -
61 cm (Table 4), the greatest TRL in all the root width classes in the stress treatment at
15.3 - 30.5 cm (Table 9), and the greatest RL among all root width classes analyzed at a
depth of 45.8 - 61 cm in the stress treatment (Table 11). Under moisture stress at depths
of 15.5 - 30.5 cm and when treatments were combined at depths up to 61 cm, the
genotype XAN 176 had the greatest RL in most of the root width classes (Tables 7 and
8). Results suggest that SEAS and XAN 176 allocated more of their photosynthates into
root production under water stress, maybe at the expense of aboveground production. In
the water stress treatment, the resistant check BAT 477 (nod) produced a RL that was

64

 

consistently lower in all root width classes examined than both SEAS and XAN 176
suggesting that maybe one of the mechanisms for the designation of BAT 477 (nod) as
being drought resistant is in its ability to allocate more photosynthates into shoot
production than root production under periods of water stress. How this relates to the
efficiency of this genotype still needs to be investigated. The data also suggests that most
of the genotypes invested a lot of resources into producing an increased quantity of finer
roots in the stress treatment, supporting the importance of small or fine roots in relation to
plant stress for the mining of water (Marschner, 1997; Manschadi et al., 1998).

In my study, RLD was low (Tables 12 and 13) compared to values of 0.5 - 2.0 cm
cm'3 reported by de Willigen and van Noordwijk (1987) for common bean in the 0 - 30
cm depth and 1.55 - 3.1 cm cm'3 reported by Heeraman and Juma (1993) for faba-bean in
the 0 - 30 cm depth. The low values obtained here could be a reflection of the method
used in obtaining root samples. Heeraman and Jurna’s (1993) results were obtained using
minizhizotron, core samples, and the monolith method and de Willigen and van
Noordwijk (1987) results reported using a minirhizotron. Our results were obtained by
sieving soil samples through a 2 mm mesh screen which only has the potential of
collecting an average of 55% of the root weight and only 10% of the plant TRL (Amato
and Pardo, 1994). The loss of fine roots from a 0.5 mm2 mesh sieve has been reported to
vary according to root integrity related to plant age (Boehm, 1979). Similarly, Amato
and Pardo (1994) found that different methods of sample preparation could affect root
integrity and therefore change the amount of fine roots retained by coarse sieves.

The high RLD exhibited by the genotype XAN 176 shows this genotype’s

65

potential for producing a deep and expansive root system even in water stress
environments which is also reflected in the production of finer roots deeper into the soil
profile (Tables 7 and 8). High RLD in the surface layer is a favorable characteristic of
crops in semiarid areas to allow for ready absorption of water after rain and to minimize
evaporation (Lampurlanes et al., 2001). Root growth deep in the soil profile allows a
crop to explore a greater volume of soil and consequently to access more water (Box,
1996). Root LD normally increases from date of planting of annuals and decreases with
soil depth and environmental root stress (Box, 1996). Results from this study showed
RLD started to decrease at a depth of 45 cm (Table 12) which is in agreement with other
studies reported in the literature (de Willigen and van Noordwijk, 1987; Heeraman and
Juma, 1993).

Shoot and root dry weight and R/S

Abscisic acid increased root and shoot dry weights at 21 DAT and increased
root/shoot ratio (R/S) at 21 and 28 DAT (Table 14). The ABA treatment increased both
shoot and root dry weights and R/ S over the control treatment and ABA treatment
increased shoot and root growth by 47 and 49%, respectively, at14 DAT and 21 DAT
while shoot and root increased by 31 and 37%, respectively, in the control treatment.
However, between 21 DAT and 28 DAT, the control treatment had a higher increase in
shoot and root dry weight (Table 14).

Control genotypic response:

In the control treatment at 14 DAT, XAN 176 had a higher shoot dry weight than
BAT 477 (nod), DOR 364 (nn), BAT 477 (rm), and DOR 364 (nod), but a root dry weight

66

only higher than DOR 364 (nn). The only difference in R/S ratio was a significantly
higher ratio in SEAS than in PR9603-22 (Table 15).

At 21 DAT, the genotype XAN 176 recorded the highest shoot and root dry
weight (Table 15). XAN 176 had a significantly higher shoot weight (P s 0.10) than all
the genotypes except PR9603-22 and a higher root dry weight (P s 0.01) than all other
genotypes except PR9603-22 (Table 15). Root\shoot ratio ranged from 0.25 to 0.53, with
the genotype SEAS having a significantly greater (P s 0.01) R/S than all other genotypes.

At 28 DAT, there was no significant difference observed among the genotypes for
root dry weight and R/S ratio (Table 15). The genotype XAN 176 had a significantly
higher (P s 0.05) shoot weight than all the genotypes except BAT 477 (nod), PR9603-22,
BAT 477 (rm), and DOR 364 (nod) (Table 15).

ABA genotypic response:

In the ABA treatment, at 14 DAT, only R/ S ratio was statistically significant with
the genotypes 8-42-M-2 and DOR 364 (nod) having a significantly greater (P s 0.01) R/S
than the genotypes PR9603-22, DOR 364 (rm), and XAN 176, but not significantly
higher than the other genotypes (table 16).

At 21 DAT, there was no significant difference among the genotypes for shoot dry
weight (Table 16). The genotype SEAS had a significantly higher (P s 0.05) root dry
weight than BAT 477 (nod), DOR 364 (nn), BAT 477 (nod), and DOR 364 (nod) and a
significantly higher (P s 0.05) R/S ratio than PR9603-22, DOR 364 (rm), and BAT 477
(nn) (Table 16).

At 28 DAT, DOR 364 (nn) had a significantly higher (P s 0.01) shoot dry weight

67

than BAT 477 (nod), PR9603-22, BAT 477 (rm), and DOR 364 (nod) (Table 16). The
genotype 8-42-M-2 had a significantly higher (P s 0.01) root dry weight than all the other
genotypes except DOR 364 (nn), XAN 176, and SEAS (Table 16). Root\shoot ratio
ranged from 0.30 to 0.52 with the genotypes SEAS and 8-42-M—2 having a significantly
higher (P s 0.10) R/S ratio than PR9603-22 and DOR 364 (nn) (Table 16).

The genotype XAN 176 consistently had one of highest shoot and root dry
weights in the control treatment. The genotype SEAS had one of the highest root dry
weights and R/S ratios at 14 and 21 DAT. In the ABA treatment, there was no consistent
performance among genotypes with regard to shoot dry weight. The top performers for
root dry weight and R/S ratio were SEAS and 8-42-M-2, both type III beans. In the ABA
treatment at 14 and 28 DAT, DOR 364 (nod) had a higher R/S ratio than DOR 364 (nn),
due to the lower shoot dry weight of the nodulating line.

PVC genotypic response:

Water deficit significantly decreased the accumulation of dry matter in leaves (P 5
0.001), stems (P .<. 0.01), reproductive parts (P s 0.05), shoots (P 3 0.001), and roots (P s
0.05) in the PVC treatment and increased R/S ratio (P s 0.10) (Table 17). There were no
significant genotypic differences for leaf, stem, and shoot dry weight and R/S ratio for
combined data (stress and nonstress combined) but there were significant differences
among the genotype for reproductive parts (P 5 0.001) and root dry weight (P s 0.10)
(Table 18). The genotype SEAS had a greater reproductive dry weight than all the
genotypes except BAT 477 (nod) and PR9603-22. SEAS and XAN 176 had a higher root
dry weight than DOR 364 (rm) and DOR 364 (nod) somewhat similar to SEAS's relative

68

performance to DOR 364 (nod) and DOR 364 (nn) in the growth pouch studies. BAT
477 (nod) had a lower root dry weight under stress than did BAT 477 (nn). Results
suggest that the greater drought resistance of BAT 477 (nod) in comparison to 8-42-M-2
is not due to decreased root length of 8-42-M-2.

When analyzed by water treatment there was significant genotypic difference for
stem, reproductive parts, and root dry weight in the stress treatment and reproductive
parts and W8 ratio in the nonstress treatment (Table 19). In the stress treatment, the
genotype PR9603-22 had a significantly higher (P s 0.10) stem dry weight than BAT 477
(nod), DOR 364 (nn), ICA Palmar, and SEAS (Table 19). The genotype SEAS had a
significantly higher (P s 0.01) reproductive dry weight than all the genotypes except
PR9603-22 and a significantly greater (P s 0.01) root dry weight than all the genotypes
except BAT 477 (nn) (Table 19). In the nonstress treatment, again SEAS had a
significantly greater (P s 0.05) reproductive dry weight than all the genotypes except
BAT 477 (nod), PR9603-22, and BAT 477 (nn) (Table 19). The genotype XAN 176 had
the highest R/S ratio (P s 0.10) among the genotypes in the nonstress treatment (Table
19).

The data show that some genotypes allocated a higher proportion of biomass to
roots than others and support the concept that root growth in dry soils is usually reduced
less than shoot growth, leading to a typical increase in R/S ratio in response to drought
stress (Waisel et al., 1996).

The performance of XAN 176 and SEAS is quite intriguing. Both genotypes
demonstrated that more photosynthates were allocated to root production during water

69

stress, however, the yield reported for both of these genotypes (Table 2, chapter I) is
quite different. The genotype XAN 176 produced yields in excess of 1000 kg ha" in both
irrigated and rainfed conditions compared to SEAS which produced approximately 600
kg ha'l under both irrigated and rainfed conditions. The low yield of SEAS is probably
explained by the fact that SEAS experienced heavy infestation by Cercospora, common
bacterial blight infection, and ozone injury, all of which undoubtedly had an impact on its
yield. It could also be speculated from this study that XAN 176 allocated more
photosynthates into seed production instead of shoot production than SEAS. Generally,
BAT 477 (nn) outperformed BAT 477 (nod) in PVC and growth pouch studies with
regard to shoot and root growth and RLD whenever significant differences or tendencies
occurred, while DOR 364 (nod) usually outperformed DOR 364 (nn).

Water stress increases root-shoot ratio and the ratio of root to shoot growth varies
widely between plant species and is strongly modified by external factors (Marschner,
1997). In annual species competition for photosynthates between shoot and roots
becomes the dominant factor during reproductive growth in limiting root growth and
activity. The proportion of photosynthates allocated belowground and used for fine root
production can be up to 44% in a tropical broadleaf stand (Cuevas et al., 1991). For
example, in maize seedlings without drought stress the R/S ratio is 1.45 compared with
5.79 under drought stress (Sharp et al., 1993). The results gathered from this study
support previous reports (El Nadi et al., 1969; Muchow, 1985; Haggani and Pandey,
1993; Manthe, 1994) for beans grown under drought environment.

Conclusion

70

 

The ABA treatment increased TRL on all sampling dates over the control
treatment and increased the production of finer roots at 21 DAT. The susceptible check,
8-42-M-2, produced significantly greater RL (5.47 m) than the resistant check BAT 477
(nod) (2.42 m), and the ABA treatment increased 8-42-M-2 TRL two-fold between each
harvest date. Fine roots (5 1.0 mm diameter) made the largest contribution to total root
length in both stressed and nonstressed treatments, suggesting that water absorption may
be more associated with fine than large roots. Water stress treatment reduced TRL by
approximately 75, 38, and 38%, respectively, at depths of 0 - 15, 15.1 - 30.5, and 0 - 92
cm.. Root length density was low, probably reflecting the method used to obtain
samples. The genotypes XAN 176 and SEAS allocated a higher proportion of biomass to
roots than did other genotypes. Results suggest that some genotypes produce a greater
portion of roots in root width classes 1, 2, and 3, indicating that fine roots may be a
meaningful trait that plant breeders can use in their efforts to breed for drought resistance

in common bean.

71

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77

 

 

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87

Table 10. Root length (cm) of nine common bean (Phaseolus vulgaris L.) genotypes of root width classes
1, 2, 3, 4, and 10 at 15.3 - 30.5 cm depth grown in 0.92 m polyvinyl chloride (PVC) tubes of 30
cm diameter in a glasshouse at Michigan State University, East Lansing, M1. at 27°C 3: 2 day/night
temperatures and a 15 h photoperiod under moisture stress conditions. Means :t SE, n = 3.

 

 

Class 1 Class 2 Class 3 Class 4 Class 10
Genotvpes O - 0.5 mm 0.51 - 1.0 mm 1.01 - 1.5 mm 1.51 -2.0 mm > 4.5 mm
Stress treatment
BAT 477 (nod) 2028 be" 324.30 c" 28.22 abc" 2.41 bc+ 5.91 bc“
PR9603-22 2255 be 335.72 bc 18.44 c 1.75 c 5.53 c
DOR 364 (nn) 1868 c 312.65 c 18.57 c 1.48 c 5.65 c
lCA Palmar 2192 be 405.02 be 32.02 abc 5.10 a 7.03 abc
XAN 176 3605 a 617.55 a 38.65 a 4.69 ab 9.34 ab
BAT 477 (nn) 3186 ab 411.55 be 38.12 a 3.33 abc 9.24 ab
SEAS 2036 be 489.27 abc 27.10 abc 3.13 abc 6.70 abc
8-42-M-2 3189 ab 520.43 ab 35.78 ab 4.70 ab 9.80 a
DOR 364 (nod) 2006 bc 312.60 c 23.97 bc 4.60 ab 4.97 c
Mean 2485 414.34 28.98 3.47 7.13
Genotypes Nonstress treatment
BAT 477 (nod) 4831 nsi 869.05 ns 48.0] ns 6.16 ns 14.14 ns
PR9603-22 4029 1 113.0 56.63 8.56 14.20
DOR 364 (nn) 3351 663.55 40.33 5.03 11.20
ICA Palmar 4618 838.68 78.12 8.79 12.64
XAN 176 4147 948.17 80.00 13.4 12.44
BAT 477 (nn) 4946 925.23 48.92 4.25 13.84
SEAS 2417 588.39 44.66 5.13 8.056
8-42-M-2 3375 766.86 64.40 8.38 11.64
DOR 364 (nod) 4203 937.88 44.63 4.28 10.90
Mean 3991 850.06 56.19 7.11 12.12

 

". *, +. Indicates significance at 0.01, 0.05, and 0.10, respectively, according to DMRT.
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89

Table 12. Total root dry weight (RDW), root length (RL), average root diameter (RD), average root
surface area (RSA), average root volume (RV), and root length density (RLD), for all root width
classes of common bean plants grown in 0.92 m polyvinyl chloride (PVC) tubes of 30 cm
diameter in a glasshouse at Michigan State University, East Lansing, M1. at 27°C :h 2 day/night

temperatures and a 15 h photoperiod under stressed and non-stressed conditions. n = 27.

 

RDW RL RSA RD RV RLD
(g) (m) (cmz) (mm) (cm’) (cm cm")

0 - 15.2 cm depth
Stress 010*" 8.73" 96.7" 0.33 n51 088“" 0.07“
Nonstress 0.41 33.33 371.9 0.32 3.55 0.27
15.3 - 30.5 cm depth
Stress 0.20* 29.40" 289.6“ 0.29M 2.48" 0.24“
Nonstress 0.35 49.19 517.2 0.31 4.72 0.40
30.6 - 45.7 cm depth
Stress 0.25 ns 40.95 ns 432.7 ns 0.30 ns 4.0 ns 0.34 ns
Nonstress 0.36 59.92 642.8 0.30 6.0 ’ 0.49
45.8 - 61 cm depth
Stress 0.17 ns 33.17 ns 372.7 ns 0.27 ns 3.6 ns 0.27 ns
Nonstress 0.27 42.90 523.6 0.25 4.8 0.35
61.1 - 76.2 cm depth
Stress 0.10 ns 18.56 ns 217 ns 0.14 ns 2.2 ns 0.15 ns
Nonstress 0.15 23.32 291 0.14 3.1 0.19
76.3 - 92 cm depth
Stress 0.01+ 1.30 ns 19.2 ns 0.07“ 0.24 ns 0.01 ns
Nonstress 0.02 1.65 26.0 0.1 1 0.34 0.01

.-.

 

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90

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Table 14. Dry weight (g) of shoot and root and root\shoot ratio of eight common bean
genotypes germinated in a germination chamber for 4 d at 25°C and transplanted
to an environmentally controlled growth chamber for 28 d at 23/20°C day/night
temperatures and a 15 h photoperiod and grown under control conditions in half-

strength Hoagland’s solution or in 10'6 M ABA solution. n = 32.

 

 

 

 

 

Treatment 14 DAT 21 DAT 28 DAT
Shoot

ABA 0.373 nsi 0659* 0.976 ns

Control 0.373 0.522 0.858
Root

ABA 0.139 ns 0.264" 0.395 ns

Control 0.124 0.186 0.296

R/S ratio
ABA 0.373 ns 0398* 0.418+
Control 0.337 0.357 0.347
1 Indicates no significant difference among means within a column.

**, *, + Indicates significant difference among means within a column at P s 0.01, 0.05,

and 0.10, respectively, according to DMRT.

92

 

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94

Table 17. Dry weight (g) of leaves, stems, reproductive parts, shoots, and root and
root/shoot ratio of nine common bean genotypes grown in 0.92 m polyvinyl
chloride (PVC) tubes of 30 cm diameter in a glasshouse at Michigan State
University, East Lansing, M1. at 27°C i 2 day/night temperatures and a 15 h

photoperiod under stressed and non-stressed moisture conditions. n = 27.

 

 

Leaf Stem Repro. Shoot Root R/S ratio
Stress 3.41 *** 2.72” 068* 5.85*** 084* 017+
Non-stress 9.75 4.33 1.32 16.4 1.60 0.10

 

 

***, **, *, +. Indicates significant difference among means within a column at P g

0.001 , 0.01, 0.05, and 0.10 respectively, according to DMRT

95

Table 18. Dry weight (g) of leaves, stems, reproductive parts, shoots, and root and

root/shoot ratio of nine common bean genotypes grown in 0.92 m polyvinyl

chloride (PVC) tubes of 30 cm diameter in a glasshouse at Michigan State

University, East Lansing, M1. at 27°C :t 2 day/night temperatures and a 15 h

photoperiod under stressed and non-stressed moisture conditions. n = 6.

 

 

 

Genotypes Leaf Stem Repro. Shoot Root R/S ratio
BAT 477 (nod) 7.04 n51 3.63 ns 1.73 ab"“ 12.4 ns 1.22 abc+ 0.12 ns
PR9603-22 5.66 4.53 1.55 abc 11.7 1.14 abc 0.10
DOR 364 (nn) 5.76 3.00 0.59 bcd 9.31 0.83 c 0.17 1‘
ICA Palmar 7.26 2.91 0.00 d 10.2 1.20 abc 0.14
XAN 176 6.71 4.06 0.32 cd 11.1 1.51 a 0.14
BAT 477 (nn) 7.90 3.43 1.05 bcd 12.4 1.24 ab 0.12
SEAS 5.93 2.83 2.61 a 11.4 1.45 a 0.15
8-42-M-2 7.10 4.30 0.58 bcd 12.0 1.30 ab 0.14
DOR 364 (nod) 5.86 3.20 0.56 bcd 9.62 1.00 be 0.1 1
Mean 6.58 3.54 1.00 11.13 1.20 0.13

I Indicates no significant difference among means within a column.

***, + Indicates significant difference among means within a column at P 5 0.001 and

0.10, respectively, according to DMRT.

96

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Chapter 3
Nitrogen fixation and partitioning of nine Caribbean and Central American
common bean (Phaseolus vulgaris L.) lines grown under rainfed and glasshouse
conditions.
Abstract
Common bean is grown on more than 12 million ha and constitutes the most

important food legume for more than 500 million people in Latin America, the

Caribbean, and Africa. This study was conducted to assess genotypes for N fixation, N-
use efficiency, and N harvest index. Field studies were conducted in 1999 and 2000 at

the Agricultural Experiment Station in St. Croix, United States Virgin Islands to
determine the N2 fixing capacity of nine common bean lines grown under irrigated and
rainfed field conditions. The total N difference method was used to estimate N2 fixation
with non-nodulating (nn) isolines of BAT 477 and DOR 364 as the reference crops. BAT
477 [nodulating (nod)] was one of the genotypes with the highest root-N concentration.
ICA Palmar had the highest stem-N concentration. Leaf-N concentration was highest in
8-42-M-2 in 1999 and in DOR 364 (nn) in 2000. Nitrogen HI values among genotypes
ranged from 7 to 76%. Nitrogen use efficiency did not differ among irrigated and rainde
treatments in 1999 but was greater in the irrigated treatment in 2000. XAN 176 produced
a high NUE and high NHI. Total N-fixed among the genotypes was low and ranged from
no fixation (—34.3 kg ha") to 19.9 kg ha", with DOR 364 (nod) producing the highest
numerical fixation both years. The reference crop DOR 364 (rm) gave a higher estimate

of N-fixation than did BAT 477 (rm).

98

Introduction

Many important common bean (Phaseolus vulgaris L.) producing areas of the
world experience moisture deficits during the growing season (Ehleringer et al., 1991),
thus emphasizing the need to breed for drought resistance. Such efforts can be greatly
aided by an increased understanding of the physiological responses which enable beans to
survive drought with minimal yield reductions. Beans have a high protein content,
approximately 26% (Bressani and Elias, 1980), and most of the N in the crop at harvest is
located in the seed. Therefore, it is important to know the impact that water deficits may
have on N partitioning and remobilization.

A number of studies have evaluated the importance of symbiotic N fixation in the
N economy of bean, based on total N acquisition and the allocation of symbiotically fixed
N to reproductive and vegetative tissues (Dubois and Burris, 1986; Kucey, 1989; Rennie
and Kemp, 1984; Lynch and White, 1992; Foster et al., 1995). Westermann et al. (1985)
reported general N distribution patterns in bean plants grown in small pots of perlite in a
greenhouse.

In the tr0pics, soil organic matter declines rapidly with cultivation (Boddey et al.,
1997; Vlek et al., 1997). Where inputs are limited, changes in soil organic matter
following cultivation quickly lead to low soil fertility and to diminished soil structure,
water holding capacity, and biological activity (V lek et al., 1997). Studies conducted in
temperate environments may not apply to tropical environments, which differ
significantly from temperate environments with regard to photoperiod, temperature,
humidity, and radiation, all of which might influence senescence and N allocation (Lynch

99

and White, 1992).

Because soil N deficiency is common in the tropics and subtropics (Graham,
1981; Dakora and Keya, 1997), N supply, N management, and N-use efficiency are
significant factors in crop production in these regions and spark intermittent concern
about the availability of fossil fuel reserves for future fertilizer N production (Graham and
Vance, 2000). The objective of this study was to investigate N fixation among several

Caribbean and Central American common bean genotypes under limiting and non-

limiting moisture regimes. This information may be useful in identifying opportunities

for genetic improvement of N-use efficiency of common bean lines for Latin America,

the Caribbean, and Africa.

Materials and methods

Field Study

Two experiments were conducted at the Agricultural Experiment Station,
University of the Virgin Islands, Kingshill, St. Croix, United States Virgin Islands
(U.S.V.I.) in 1999 and 2000. Mean air temperature was 26.10 C. Seeds were planted on
9 March and harvested on 1 June 1999 and on 6 April and harvested on 27 June 2000
(stress plots) and on 30 June 2000 (non-stress plots). The soil at the Agricultural
Experimental Station field site is classified as a Fredensborg loamy, fine carbonatic,
isohyperthermic, shallow, Typic Calciustoll with pH ranging from 7.6 to 8.4.

In 1999, soil samples from each plot were taken and analyzed by the Michigan

100

 

State University Plant Nutrient and Soil Testing Laboratory for N, P, K, Zn, Mn, and Cu.
As indicated by the soil analysis, 22 kg P/ha", 5.6 kg Zn/ha", and 10 kg Mn/ha" were
applied in 1999 and 2000. No N fertilizer was applied, since N fixation was being
assessed. Samples from each block (stress and non-stress) were taken in 2000.

In 1999, applications of insecticide, Sevin 80WP (0.68 kg ai/A) and Diazinon

 

AGSOO (170 g ai/A), were made at one week intervals starting on 26 March to control
bean leafskeletonizer. One application of fungicide, Benomyl (500g per 95 L/A) and M-
Pede (Potassium salts of fatty acids) (71 g per 3.8 L/A) was made on 18 April for control
of Cercospora (C ercospora canescens). No insecticides or fungicides were applied to
field plots in 2000.

Plant material

Nine common bean genotypes possessing Type I, II, or 111 grth habits (Table 1)
were included in this study: BAT 477 [nodulating (nod) and non-nodulating (nn)], DOR
364 [nodulating (nod) and non-nodulating (nn)], XAN 176, ICA Palmar, 8-42-M-2,
SEAS, and PR9603-22, local check (obtained from Dr. James Beaver, University of
Puerto Rico-Mayaguez Campus). BAT 477 (nod) and 8-42-M-2 were the drought
resistant and drought susceptible checks, respectively. Seeds were inoculated with a
granular form of Rhizobium etIi, which was applied within the furrow.

Experimental design

The study utilized a randomized complete block design with four replications,
moisture as the main plot, and genotype as subplot. In 1999, seeds were planted into
four-row plots of 0.5 m row spacing and 2.48 m length. Each row was planted at a

101

density of 25 seeds and thinned to 23 plants. In 2000, seeds were planted into four-row

 

plots of 0.5 m row spacing and 2.13 m length and planted at a density of two seeds per
station at 7.62 cm between stations. Moisture stress was initiated at the V3 growth stage
or 20 DAP (days after planting) by cessation of irrigation to the rainfed plots. Control
plots were maintained at a soil moisture content of -30 kPa.

Data collection

In 1999, plants were sampled at V3, R2, and R7 and in 2000 at V3, R4, and R8

 

growth stages (Nuland and Schwartz, 1989). At sampling, three plants per plot were
extracted from the soil, dipped in water to remove all soil and debris, and separated into
leaves, stems, roots, and reproductive parts (flowers and/or pods) for dry weight and total
N determination. Nitrogen was determined by Kjeldahl digestion and total N analysis
was done using the Latchet procedure. Dry plant material was ground in a Udy cyclone
sample mill (Udy Corporation, Fort Collins, Co.) to pass through a 2-mm screen. Plant
samples of 0.1 g were digested in 4 ml of 18 M H2804 with 1.5 g K2S04 and 0.075 g Se
catalyst.

N ,fixation

Nitrogen fixation was determined by the difference method. Two non-nodulating
bean lines [BAT 477 (rm) was obtained from Dr. Steven Beebe (CIAT) and DOR 364
(nn) from Dr. James Beaver (University of Puerto Rico-Mayaguez campus)] were utilized
as reference crops. The difference in the total N accmnulated by the nodulating lines and

the non-nodulating control is regarded as the amount of N2 fixed (Smith and Hume, 1987;

102

Ayisi et al., 1992; Ohdan and Daimon, 1998). Thus: N2 fixed = N M.,, ,,‘,. mululating ”m, - Nfimm
00-0/000,; n...» The major assumption of this method is that the nodulating lines and the
non-nodulating lines take up identical amounts of N from the soil.

Glasshouse study

Plants were grown in polyvinyl chloride tubes (PVC) for 40 days in a glasshouse
at Michigan State University, in East Lansing, MI. The temperature regime was 27°C i
2°C and light intensity was 1421 uE ”1-25-1 with a 15 h photoperiod. The experimental
design was a split plot with water (stressed and non-stressed) as the main plot, genotypes
as the subplot, and three replications. The PVC tubes were one meter in length with a
diameter of 30.5 cm. Five seeds per PVC tube were planted on 7 August, 2000 and
thinned to one plant per PVC tube at 14 days after planting (DAP). Stress was initiated at
14 DAP by cessation of water to plants in the stress treatment. Plants were sampled at
R1/2 growth stage (40 DAP). Stem, leaf, and reproductive parts were weighed and dried
at 60°C for 48 h, re-weighed and then ground to pass through a 2 mm screen Udy
Cyclone Sample Mill (Udy Corporation, Fort Collins, CO.) And analyzed for total
nitrogen.

Statistics

The MSTAT micro-computer statistical package (Michigan State University) for
agricultural sciences was used for all data analysis.

Results and discussion
N-Partitioning
Water effect

103

 

Moisture stress did not significantly affect root-N concentration at any growth
stage in either year (Table 1). There were no significant differences in stem-N
concentration between the irrigated and rainfed moisture conditions of the field study on
any of the sampling dates except at the V3 growth stage (P s 0.10) in 2000 where
irrigated plants had a lower stem-N concentration (Table 1). Leaf-N was significantly
lower under rainfed conditions than under the irrigated treatment at the R7 growth stage
in 1999 and significantly higher on all sampling dates in 2000. There were no significant
differences in leaf-N concentration between stressed and nonstressed moisture treatments
in the PVC experiment (Table 1). Reproductive-N was greater in the irrigated treatment
than rainfed at the R7 (P s 0.05) growth stage in 1999 and in the rainfed treatment at the
R4 (P s 0.05) growth stage in 2000 (Table 1).

Root-N concentration

In 1999, there were significant genotypic differences in root-N concentration in
the combined stress and nonstress treatments at the V3, R2, and R7, at R2 and R7 under
rainfed conditions, and at V3 and R7 under irrigated conditions (Table 2). In the
combined analysis at the V3 growth stage, the genotype BAT 477 (nod) had a
significantly higher (P s 0.05) root-N concentration than the genotypes DOR 364 (nn),
ICA Palmar, and BAT 477 (nn). At the R2 growth stage, BAT 477 (nod) had a
significantly higher root N-concentration (P s 0.05) than the genotypes PR9603-22, DOR
364 (rm), and XAN 176. At the R7 growth stage, the genotype ICA Palmar, had a
significantly higher (P 5 0.001) root-N concentration than all other genotypes except
BAT 477 (nod) (Table 2).

104

In the rainfed treatment at the R2 growth stage, BAT 477 (nod) had a significantly
higher root-N concentration than PR9603-22, DOR 364 (rm), and XAN 176. At the R7
growth stage of the rainfed treatment, BAT 477 (nod) was significantly higher than all
other genotypes except ICA Palmar (Table 2). In the irrigated treatment, BAT 477 (nod)
root-N concentration was higher than PR9603-22, DOR 364 (nn), ICA Palmar and BAT
477 (nn) at both V3 (P s 0.01) and R7 (P s 0.05) (Table 2).

In 2000, genotypic root-N concentration was significantly at the R4 growth stage

 

(Table 3). The genotype ICA Palmar had a significantly higher (P s 0.10) root-N
concentration than the genotypes XAN 176 and SEAS in the combined analysis at the R4
growth stage (Table 3). In the rainfed treatment at R4 growth stage, SEAS had a
significantly lower root-N concentration than all the genotypes except XAN 176 and
BAT 477 (nn) (Table 3). Overall, BAT 477 (nod) had a high root-N concentration and
there was a tendency for a higher root-N concentration in BAT 477 (nod) than in BAT
477 (rm) and in DOR 364 (nn) than in DOR 364 (nod). Interestingly, SEAS and XAN
176 had lower root-N concentration, but a high RLD (Chapter 2). While XAN l7 6,
PR9603-22, and DOR 364 (nn) generally had a low root N-concentration, but relatively
high yield.
Stem-N concentration

In 1999, genotypic stem-N concentration was significantly different only at the
R7 growth stage in the combined, rainfed, and irrigated analysis, with the genotype ICA
Palmar having a significantly higher (P 5 0.001) concentration than all the other
genotypes and XAN 176 one of the lowest (Table 4). In 2000, there were no significant

105

differences between the genotypes for the combined and rainfed treatments of the field
study but there were significant differences at the R8 growth stage in the irrigated
treatment (Table 5) with the genotype ICA Palmar having a significantly higher (P s
0.10) stem-N concentration than all other genotypes (Table 5). In the PVC experiment,
the genotype ICA Palmar again had the highest stem-N concentration but was only
statistically different than the genotype PR9603-22 in the combined analysis and than
PR9603-22 and 8-42-M-2 in the nonstress treatment (Table 5).

Leaf-N concentration

In 1999 at the R2 growth stage in the combined analysis, the genotypes 8-42-M-2
and ICA Palmar had a significantly higher (P s 0.05) leaf—N concentration than the
genotypes BAT 477, DOR 364 (nn), ICA Palmar, and SEAS. DOR 364 (nod) had a
higher leaf-N concentration than its non-nodulating isoline. At the R7 grth stage, 8-
42-M-2 and ICA Palmar had a significantly higher leaf-N concentration (P 5 0.001) than
PR9603-22, DOR 364 (rm), and DOR 364 (nod) (Table 6). In the rainfed treatment, DOR
364 (nod) had one of the highest (P s 0.10) leaf-N concentrations at the R2 growth stage
and the genotype ICA Palmar had one of the highest (P s 0.01) leaf N-concentration at
the R7 growth stage (Table 6). In the irrigated treatment, the genotype SEAS was among
the genotypes with the highest leaf-N at the V3 growth stage and the genotype 8-42-M-2
was among the highest at both R2 and R7 growth stages (Table 6). In 2000 significant
genotypic differences were only observed at the V3 growth stage for combined, rainfed,
and irrigated analyses of the field study at the UVI field trial (Table 7). The genotype
DOR 364 (nn) had one of the highest leaf-N concentrations in all three analyses (Table

106

 

7). There were no significant genotypic differences observed in the PVC experiment for
the combined and nonstress analyses but in the stress analyses the genotype DOR 364
(nn) again had one of the highest leaf-N concentrations but was not statistically different
from the genotype XAN 176 (Table 7).

Reproductive-N concentration

In the combined analyses at the R2 growth stage in 1999, the genotype DOR 364
(nod) had significantly higher (P g 0.001) combined pod and seed-N concentrations than
all of the other genotypes, but had one of the lowest pod-N and seed N-concentrations by
the R7 growth stage (Table 8). At the R7 growth stage in 1999, ICA Palmar had a
significantly higher (P 5 0.001) pod N concentration than the genotypes PR9603-22,
DOR 364 (rm), and XAN 176. In the rainfed treatment, the genotype ICA Palmar had
one of the highest pod-N concentrations at both R2 and R7 growth stages and SEAS had
one of the highest seed-N concentration at R7 (Table 8a). In the irrigated treatment, the
genotype DOR 364 (nod) had one of the highest pod-N concentrations at the R2 growth
stage and the genotype BAT 477 (nod) had one of the highest at the R7 growth stage
(Table 8b). In 1999, there was a tendency for DOR 364 (nod) to have a higher
reproductive-N concentration than DOR 364 (nn) but for BAT 477 (nod) to have a lower
reproductive-N concentration than BAT 477 (nn). Similarly, BAT 477 (nn) tended to be
one of the genotypes with a higher reproductive-N concentration, while DOR 364 (nn)
tended to be one of the lines with a lower reproductive-N concentration. The relative N
fixation using BAT 477 (rm) and DOR 364 (nn) reflect these trends.

In 2000, there were no significant genotypic differences in reproductive-N

107

 

concentration in the combined and irrigated analyses of the field study but seed-N was
significantly different in the rainfed analyses at the R8 growth stage with the genotype
XAN 176 having one of the lowest concentrations (Table 9). In the PVC experiment, the
genotype XAN 176 had a significantly higher (P .<. 0.001) reproductive-N concentration
at the R2 growth stage than all other genotypes in both combined and stressed analyses,
except the genotypes BAT 477 (nn), 8-42-M-2, and DOR 364 (nod) (Table 8). However,
in the nonstress analyses, XAN 176 was only significantly higher (P s 0.01) than
PR9603-22 (Table 9).

Nitrogen flow from pods could also have been a significant source of seed N. The
decline in pod-N concentration differs with the observations of Oliker et a1 (1978), who
concluded that N in pod walls was not available for seed growth of common bean and in
fact proposed that pod walls competed with seeds for N. This discrepancy may be due to
the fact that Oliker et al. (1978) used a snap bean genotype in their studies. Snap beans
have been selected for pod development rather than seed development and may have very
different N allocation patterns than common bean genotypes.

Nitrogen harvest index (NHI)

Nitrogen harvest index (NHI) was significantly reduced (P s 0.01) in 1999 in the
nonstress moisture treatment, but in 2000 there was no significant different between
moisture treatments. This contrasted with results reported by Foster et al. (1995), who
observed a reduced NHI under moisture stressed conditions, the 1999 results may reflect
the common bacterial blight (Xanthomonas campestris pv. phaseoli) and Cercospora
(C ercospora canescens) infestations that heavily affected the non-stress plots (Chapter 1).

108

There were significant combined, rainfed, and irrigated genotypic differences for NHI in
1999 but not in 2000 (Table 10). In 1999, the genotype DOR 364 had a significantly
higher (P g 0.001) combined NHI than the genotypes 8-42-M-2, SEAS, and ICA Palmar
and the genotypes XAN 176 and PR9603-22 had a significantly higher (P 5 0.001) NHI
in the rainfed treatment than ICA Palmar, BAT 477 (rm), and SEAS but not significantly
different than the other genotypes (Table 10). In the irrigated treatment, the genotype

DOR 364 (nod) again had the highest NHI but was only statistically different (P s 0.01)

 

from ICA Palmar and 8-42-M-2 (Table 10).

Nitrogen harvest index values among the genotypes ranged from 7 to 76%. These
results are in the range reported previously for NHI reported by Foster et al. (1995) (P.
vulgaris); Thomas and Hungria (1988) (P. vulgaris); and Bnmner and Zapata (1984) (V.

faba), who all reported ranges from a low of 18% to a high of 91 percent. There was a
highly positive significant correlation between seed weight and NHI in 1999 (0.90***)
and 2000 (0.81 ***). Also, significant correlations occurred between NHI and harvest
index (H1) in 1999 (0.99**"‘) and in 2000 (0.97***). High NHI represents the increased
capacity of a genotype to mobilize and translocate nitrogen from the leaves, stems, and
roots to the seed of the plant.

Nitrogen harvest index, which is a measure of the total nitrogen content of the
seeds versus that in the portion of the plant above the ground, has been shown to be
subject to considerable variation. The capability of effective transfer of nitrogen from
above ground biomass to the seed has been documented in many crops [wheat (T riticum
aestivum) McKendry et al. (1988); Desai and Bhatia (1978), oats (Avena saliva) Kairudin

109

and Frey (1990); Rattunde and Frey (1986), corn (Zea mays) Katsantonis et al. (1988).
and soybean (Glycine max) Shiraiwa and Hashikawa (1995); Chandel et al. (1989)].
These studies have presented values for NHI as high as 80-84%. In these crops, it is
doubtful whether a further portion of the nitrogen remaining in the aboveground biomass
could be transferred to the seed.

Harvest index (H1)

The harvest index (HI) represents the increased capacity of a plant to translocate

photosynthates from other plant organs to the seed (Donald and Hamblin, 1976). In

 

1999, harvest index was significantly increased in the moisture stress treatment (P s 0.05)
but not in 2000, although there was a tendency for this to occur. As with the analysis for
NHI, there were significant genotypic differences for combined, rainfed, and irrigated
treatments in 1999 but not in 2000 (Table 11). The genotype DOR 364 had a
significantly higher (P g 0.001) combined H1 in 1999 than the genotypes ICA Palmar and
8-42-M-2 but not significantly higher than the other genotypes (Table 11). In both
rainfed and irrigated treatments, the genotype ICA Palmar reported the lowest HI (Table
1 1) due to the fact that ICA Palmar did not mature or produce seed-N from most of the
plots. Harvest index values are in agreement with those of Brunner and Zapata (1984)
with faba bean (Viciafaba minor) and those obtained by Foster et al. (1995) with
common bean. Harvest index values among the genotypes ranged from 6 to 41% in 1999
and from 25 to 40% in 2000 (Table 11) with DOR 364 (nod & nn), XAN 176, PR9603-22
having one of the highest H1 in 1999.

Significant correlations occurred between HI and seed weight in both years of the

110

study (0.93*** and 0.86***, for 1999 and 2000, respectively). These results suggests
that HI might be an efficient tool for evaluating common bean lines for adaptation to
water deficits. However, care must be taken, although an increased HI may contribute to
the increased yield potential of a genotype it may not be the greatest contributor to that
genotype yield improvement (Kumudini et al., 2001). Reports on the association between
increased HI and seed yield in soybean have been found to be contradictory. Some
reports suggest that there’s no correlation between an increased HI and soybean yield
(Schapaugh and Wilcox, 1980; Morrison et al., 1999; Shiraiwa and Hashikawa, 1995) and
others suggest that theirs is (Frederick et al., 1991).

Nitrogen use efficiency (N UE)

Nitrogen use efficiency (NUE) did not differ among irrigated and rainfed
treatments in 1999 either as seed NUE or as total NUE. In 2000, seed-NUE was
significantly greater (P s 0.10) in the rainfed treatment and total-NUE was greater (P s
0.01) in the irrigated treatment. In 1999, when NUE was calculated as total-NUE, the
genotype DOR 364 (nn) had the highest (P g 0.001) NUE of all the genotypes except
PR9603-22 in the combined harvest. It was significantly higher (P s 0.05) than all the
other genotypes in the rainfed treatment and significantly higher (P s 0.01) than XAN
176, BAT 477 (rm), and SEAS in the irrigated treatment (Table 13).

When NUE was calculated as seed-NUE the genotype ICA Palmar was not
included in the analyses. The genotype DOR 364 (rm) still recorded the highest NUE of
all the genotypes for combined, rainfed, and irrigated treatments (Table 13). The
genotype SEAS consistently recorded one of the lowest total- and seed-NUE in 1999.

111

 

Significant genotypic differences were only detected in the rainfed treatment for both
total-NUE (P s 0.10) and seed-NUE (P s 0.05) in 2000, with the genotype XAN 176
having the highest NUE in both total- and seed-NUE (Table 14). From these results, it
seems as though the genotype XAN 176 appears to be the most efficient of the genotypes
with regard to NUE.

Nitrogen fixation

The N difference method was used to estimate N2 fixation in this study. Two

 

reference crops, BAT 477 (rm) and DOR 364 (um) were utilized. In 1999, when BAT 477
(nn) was used as the reference crop, there was no significant difference between the two
treatments and virtually no fixation occurred (Table 15). However, when DOR 364 (nn)
was used as the reference crop, greater fixation (P s 0.10) occurred in the irrigated
treatment. The same trend continued in 2000. When the genotype DOR 364 (nn) was
used as the reference crop, significant differences occurred between the treatments but not
when BAT 477 (nn) was used as the reference crop (Table 15). However, all N fixation
values were exceedingly low.

There were significant genotypic differences in 1999 when both BAT 477 (rm)
and DOR 364 (nn) were used as the reference crop whereas there was no significant
difference among the genotypes when either BAT 477 (nn) or DOR 364 (nn) was used as
the reference crop in 2000 (Table 16). In 1999, with both reference crops, the genotype
DOR 364 (nod) had significantly higher N fixation (P s 0.05) than the genotype ICA
Palmar but not significantly higher than the other genotypes (Table 16). The amount of
N-fixed in 1999 ranged from a low of -34.9 kg ha'1 (ICA Palmar with BAT 477 (nn) as

112

the reference crop) to a high of 19.9 kg ha'1 (DOR 364 (nod) with DOR 364 (nn) as the
reference crop). In 2000, for both reference crops the genotype DOR 364 (nod) had a
numerically higher amount of N-fixed than the other genotypes although it was not
statistically significant (Table 16). The amount of N-fixed in 2000 ranged from a low of
—1.1 kg ha" (PR9603-22 with BAT 477 (nn) as the reference crop) to a high of 5.3 kg ha"
(DOR 364 with DOR 364 (nn) as the reference crop) (Table 16).

The amount of N2 fixed by common bean reported in the literature ranges from 3
to 57 kg ha’l (Wani and Lee, 1992; Peoples and Crasswell, 1992; Wani etal., 1995). Our
results reported here are on the low end of this scale and may not be representative of the
genotype’s N2 fixing ability. In 1999, plants were severely infected with Cercospora and
common bacterial blight, contributing to a significant loss of leaf from the plant before
seed filling which may have decreased photosynthates available for the nodules and for
nitrogenase activity. In 2000, plots were located in the same location as the previous
year. Plants exhibited Cercospora, common bacterial blight, and nitrogen deficiency
symptoms. No starter fertilizer N was applied to the field in 1999 or 2000 in order to
assess N fixation and soil-N status was low to medium. It is known that common bean is
a poor N2 fixer (Westermann et al., 1981) and it has been reported that a starter fertilizer
N is usually required (Sprent and Thomas, 1984) to avoid periods of nitrogen stress in the
field. In 2000, plants exhibited symptoms of zinc and/or iron deficiency. Iron deficiency
would have interfered with nitrogenase activity helping to explain the low N fixation.
Tissue analysis for zinc and iron is in progress.

Temperature may have also impacted the amount of N-fixed. Waters et al. (1983)

113

 

stated that satisfactory N2 fixation may seldom be achieved in warm tropical locations.
These authors found poor nodulation, lower N2 fixation, and lower yields in a hot valley
relative to a cool mountainous site (at mid-day, soil temperature at 10 cm averaged 28
and 20°C, respectively). Small and Joffe (1968) and Piha and Munns (1987) reported that
N-fertilized legumes can better withstand warmer temperatures than can unfertilized
counterparts such as the case with my study. The performance of the two reference cr0p
BAT 477 (rm) and DOR 364 (nn) was unexpected. In both years of the study, N fixation
was greater using DOR 364 (an) than BAT 477 (nn).
Conclusion

BAT 47 7 (nod) was one of the genotypes with the highest root-N concentration.
XAN 176, DOR 364 (rm), and PR9603-22 had relatively high root-N concentration and
were among the highest yielding lines in the field study. ICA Palmar had the highest
stem-N concentration, probably resulting from its failure to mature and low N
remobilization from stems to seeds. Leaf-N concentration was highest in 8-42-M-2 in
1999 and in DOR 364 (nn) in 2000. Nitrogen HI values among genotypes ranged from 7
to 76% which are comparable to values reported in the literature. XAN 176 had high
NHI and H1 in 1999 and high NUE in 2000. There were significant correlations between
NHI and seed weight and between HI and seed weight suggesting that NHI and HI might
be efficient tool for evaluating common bean lines for adaptation to water deficits.
Nitrogen use efficiency did not differ among irrigated and rainfed treatments in 1999 but
were greater in the irrigated treatment in 2000. Total N-fixed among the treatments
(irrigated and rainfed) and among the genotypes was quite small and in some cases

114

 

 

negligible. N fixation was low and no fixation (-34.3 kg ha") to 19.9 kg ha". The
reference crop DOR 364 (nn) gave a higher estimate of N fixation than did reference crop
BAT 477 (nn). Genotypes varied for N-concentration of various organs, NUE, NHI, HI,

and N fixation.

115

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119

Table l. The effect of moisture stress on root, stem, leaf, and reproductive structures-N concentration (g
kg") in common bean (Phaseolus vulgaris L.) grown at the Agricultural Experiment Station at the
University of the Virgin Islands in 1999 and 2000, under irrigated and rainfed moisture conditions
and in polyvinyl chloride (PVC) tubes in a greenhouse at Michigan State University, East
Lansing, MI. in 2000, under stressed and nonstressed moisture condition. N = 36 (UVI), N = 27

 

 

 

 

 

 

 

 

(PVC).
1999--------- 2000—-——-—- PVC
Growth stage:
V3 R2 R7 V3 R4 R8 R2
Treatments: 2 kg"
Root-N
Irrigated 12.5 ns§ 8.0 ns 7.5 ns 10.3 ns 6.0 ns 8.6 ns ---
Rainfed 12.4 7.7 7.5 10.0 6.4 8.3 ---
Stem-N
Irrigated 13.5 ns 9.9 ns 7.1 ns l3.6+ 5.6 ns 7.7 ns 14.8 ns
Rainfed 11.9 9.9 6.6 14.3 6.7 8.1 14.8
_L_e.a_f_-E.
Irrigated 35.3 ns 23.2 ns 25.8“ 30.6" l6.0+ 17.0M 34.6 ns
Rainfed 35.6 20.0 21.9 32.7 19.4 19.0 35.7
Reproductive structu res-N
Irrigated --- 137.6 ns #17.2"‘ --- 17.3" 1130.3 ns 30.2 ns
Rainfed --- 37.2 14.0 --- 22.3 30.5 30.3
Irrigated --- 1:113 1.6 ns §§34.4 ns --- --- 115.6 ns ---
Rainfed --- 30.8 35.4 -- --- 5.9 ---
I Indicate stressed and nonstressed moisture conditions in the PVC experiment (Irrigated = Nonstress; Rainfed = Stress).
§ Indicates no significant differences among means within a column.
1 Indicate values from flowers within a column at R2 growth stage in 1999.
# Indicate values from pods within a column at R7 growth stage in 1999.
tt Indicate values from seeds within a column at R8 growth stage in 2000.
1: Indicate values from pods within a column at R2 growth stage in 1999.
1115 Indicate values from seeds within a column at R7 growth stage in 1999.
11 Indicate values from pods within a column at R8 growth stage in 2000.

"‘. ‘, +. Indicates significant difference among means within a column at P s 0.01, 0.05, and 0.10, respectively, according to
DMRT.

120

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125

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Table 8a. Reproductive structures-N concentration (g kg") of nine common bean (Phaseolus

vulgaris L.) genotypes harvested at three growth stages (V3, R2, and R7) grown at the

Agricultural Experiment Station at the University of the Virgin Islands in 1999 under

rainfed and irrigated moisture conditions. N = 8 (combined), 4 (rainfed or irrigated).

 

Genotypes
BAT 477 (nod)
PR9603-22
DOR 364 (nn)
ICA Palmar
XAN 176
BAT 477 (nn)
SEAS
8-42-M-2
DOR 364 (nod)

Mean

BAT 477 (nod)
PR9603-22
DOR 364 (nn)
ICA Palmar
XAN 176
BAT 477 (nn)
SEAS
8-42-M-2
DOR 364 (nod)

Mean

 

 

 

 

 

 

 

 

Combined
Growth stages
R2 (flowers) R2 (pods & seeds) R7 (pods) R7 (seeds)
38.8 abc+ 34.5 b**" 18.3 abc"* 38.6 ab"
36.1 bcd 31.1 bc 10.9 cd 32.7 be
34.5 d 28.1 cd 7.50 d 30.2 c
40.0 a 34.4 b 23.4 a 32.7 be
38.5 abc 22.3 e 13.9 bed 36.3 ab
39.6 ab 34.0 b 14.5 abcd 36.0 abc
35.5 cdl 33.8 b 21.5 ab 39.0 a
38.7 abc 24.7 de 22.0 ab 35.6 abc
38.4 abc 38.7 a 8.80 d 33.5 abc
37.8 31.3 15.6 34.9
Rainfed
36.9 mi 33.4 ab‘" 13.6 ab" 37.9 ab‘
35.7 31.2 abc 6.50 b 33.2 bc
35.3 27.3 bcd 6.91 b 30.8 c
40.0 34.8 a 25.1 a 33.1 be
38.9 21.7 d 8.28 b 34.6 abc
40.4 33.5 ab 17.6 ab 38.8 ab
33.4 32.6 ab 23.8 a 40.2 a
39.1 25.0 cd 17.3 ab 36.5 abc
39.1 37.7 a 7.02 b 33.5 be
37.6 30.8 14.0 35.4

 

127

 

Table 8b.

 

 

 

Irrigated

 

 

Growth stages

R2 (flowers) R2 (pods & seeds) R7 (pods) R7 (seeds)
Genotypes 15g:
BAT 477 (nod) 38.4 abc“ 35.6 ab*** 22.9 ab“ 39.3 a+
PR9603-22 33.0 c 31.0 be 15.3 bcd 32.3 bc
DOR 364 (nn) 35.0 be 28.9 c 8.13 d 29.6 c
ICA Palmar 36.7 abc 34.0 b 21.7 abc 32.3 bc
XAN 176 38.0 abc 22.8 d 19.4 abc 37.9 ab
BAT 477 (nn) 38.1 abc 34.3 b 11.4 cd 32.8 bc
SEAS 40.0 ab 35.0 b 19.3 abc 37.8 ab
8-42-M-2 41.6 a 24.5 d 26.5 a 34.7 abc
DOR 364 (nod) 34.6 be 39.7 a 10.6 cd 33.4 bc
Mean 37.3 31.8 17.2 34.4

 

 

 

**"', “, ‘, +. Indicates significant difference among means within a column at P 5 0.001, 0.01, 0.05, and
0.10, respectively, according to DMRT.

I Indicates no significant differences among means within a column.

128

 

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131

Table 12. Nitrogen use efficiency (NUE) of common bean (Phaseolus vulgaris L.) plants
grown under irrigated and rainfed moisture regime in a 1999 and 2000 field study
at the Agricultural Experiment Station at the University of the Virgin Islands-St.

Croix campus. The NUE was computed as total g DW / total g N or g seed DW/

 

g seed N. N = 36.
M
2 seed DW / g seed N Total g DW / Total g N

Treatment 1999
Irrigated 28 us}; 49 ns
Rainfed 29 49

2999
Irrigated 32+ 63'”
Rainfed 34 58

 

**, +. Indicates significant difference among means within a column at P s 0.01 and
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1 Indicates no significant differences among means within a column.

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_ "M-

Table 15. Nitrogen fixed (kg ha") from common bean (Phaseolus vulgaris L.) plants
grown under irrigated and rainde moisture regime in a 1999 and 2000 field study
at the Agricultural Experiment Station at the University of the Virgin Islands-St.
Croix campus. N-fixed was calculated by the difference method with DOR 364

(rm) and BAT 477 (nn) as the reference crops. N = 36.

 

N-fixed (kg ha'l)

 

 

 

BAT 477 (nn) DOR 364 (nn)
Treatment 1999
Irrigated -16.2 mi 9.69+
Rainfed . -6.13 -1 .4
2000
Irrigated 0.09 ns 4.34"
Rainfed 1.34 -O.l
1 Indicates no significant differences among means within a column.

**, +. Indicates significant difference among means within a column at P s 0.01 and

0.10, respectively, according to DMRT.

135

Table 16. Nitrogen fixed (kg ha") of nine common bean (Phaseolus vulgaris L.)

genotypes grown under irrigated and rainfed moisture regime in a 1999 and 2000

field study at the Agricultural Experiment Station at the University of the Virgin

Islands-St. Croix campus. N-fixed was calculated by the difference method with

DOR 364 (rm) and BAT 477 (nn) as the reference crops. N = 8

 

 

 

1999
Genotypes BAT 477 (an) DOR 364 (an)
BAT 477 (nod) -11.2 ab“ 4.15 ab*
PR9603-22 -11.3 ab 3.96 ab
ICA Palmar -34.9 b -l9.6 b
XAN176 0.10 a 15.4a
SEAS -3.15 a 12.1 a
8-42-M-2 -22.0 ab -6.7 ab
DOR 364 (nod) 4.37 a 19.7 a
Mean -11.2 4.12

 

 

2000
BAT 477(nn) DOR 364(nn)
2.67 nsl’ 4.9 ns
-1 .1 0.3
-0.8 0.6
-0.1 1.4
-0.4 1.0
0.80 2.2
3.90 5.3
0.71 2.25

 

*

according to DMRT.

Indicates significant difference among means within a column at P s 0.05

1' Indicates no significant differences among means within a column.

136

Summary and Conclusions
The objectives of this study were to utilize limiting and non-limiting moisture
regimes to determine (i) if selected genotypes of common beans exhibited differences in
drought resistance as measured by yield, (ii) if drought resistance genotypes had differing

root growth, and (iii) if genotypes differed in N fixation. The hypotheses were: (i)

drought resistant genotypes have a greater mass of fine roots than drought susceptible
genotypes and (ii) drought resistance genotypes have a higher N2 fixing capacity than
susceptible genotypes.

Geometric mean and the stress tolerance index (STI) gave identical rankings with
regard to genotypic drought resistance and correlated more highly with yield than did the
drought susceptibility index (DSI). Geometric mean and STI ranked PR9603-22, DOR
364 (nod), and DOR 364 (rm) among the top four genotypes in both 1999 and 2000.
Abscisic acid (ABA) increased total root length (TRL) and moisture stress decreased it.
Nitrogen fixation was low both years, ranging from no fixation (-34.3 kg ha") to 19.9 kg
ha“, possibly reflecting iron deficiency and problems resulting from infestations of
common bacterial blight (Xanthomonas campestris pv. phaseoli), Cercospora
(Cercospora canescens). Thus genotypic differences in N fixation could not be
determined.

Genotypes varied for yield, TRL, NUE, NHI, and N fixation. Growth pouch and
PVC studies identified XAN 176, SEAS, and 8-42-M-2 as having high TRL, suggesting
that growth pouches may provide a viable method for assessing root growth among

differing lines. Fine roots made the largest contribution to total root length, suggesting

137

 

 

that water absorption may be more associated with fine than large roots. The susceptible
check (8-42-M-2), produced a greater root length and a greater mass of fine roots than the
resistant check BAT 477 [nodulating (nod)] suggesting that the mechanism that help
imparts drought resistance in the resistant check may not be associated with root length
and/or the accumulation of finer roots.

Overall genotypic rankings were generated using the genotypic rankings from (i)
1999 and 2000 yield data, (ii) TRL from the ABA and control growth pouch and the
polyvinyl chloride (PVC) studies, (iii) 1999 and 2000 geometric mean, and (iv) 1999 and
2000 N fixation using DOR 364 (nn) as the reference crop (Appendix B). A ranking of
one was the highest and eight the lowest. Individual genotypic rankings were tallied and
the genotype with the lowest number was assigned a ranking of one and the genotype
with the highest number a ranking of eight. To my knowledge, a categorization of this
type has not been presented before. The overall ranking was created by giving equal
weight to each of the individual rankings. Future work may indicate otherwise, but the
proposed system is one method for processing the data to assess relative genotypic
performance. To that end, the three highest performers were DOR 364 (nod), XAN 176,

and PR9603-22.

138

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