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This is to certify that the

thesis entitled

An Investigation of the Genetics of Chip Color
in Stored Potatoes (Solanum tuberosum L.)

 

presented by
Donna H. Kells

has been accepted towards fulfillment
of the requirements for

Master of Scieaggree in Crop and Soil Sciences

 

 

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extrema-.915”. t

AN INVESTIGATION OF THE GENETICS OF CHIP COLOR
IN STORED POTATOES (Solanum mberosum L.)

By
Donna H. Kells

A THESIS
Submitted to
Michigan State Universi
in partial fulfillment of the requirements
for the degree of

MASTER OF SCIENCE

Department of Crop and Soil Sciences
1993

ABSTRACT

AN INVESTIGATION OF THE GENETICS OF CHIP COLOR
IN STORED POTATOES (Solanum tuberosum L.)

By
Donna H. Kells

Producers of chip-processing potatoes desire to produce varieties that will yield
acceptable color potato chips after long-term storage at intermediate temperatures.
Studies were conducted in 1989 and 1990 to examine the genetics of chip color in stored
potatoes. Chip color became poorer with increasing storage time. Acceptable chip—
processing ability, as determined by chip color, was correlated with lower glucose
content and lower test tape values. Sucrose content and glucose-forming-potential were
not acceptable indicators of chip-processing ability. Determination of test tape values is
useful in the early stages of a potato breeding program when large numbers of progeny
are being evaluated. Chip color evaluation is useful in the intermediate stages of a
program. Glucose and sucrose content determination is best used later in a breeding

program due to the high cost and labor requirement.

ACKNOWLEDGMENTS
I would like to express my appreciation to Dr. Dave Douches for his guidance and
assistance during this project. I would like to thank Drs. Richard Chase and Jerry Cash
for serving on my guidance committee and for their assistance with this research project.
I am also grateful for the technical assistance provided by Richard Kitchen, Katherine
Cullen, Theresa Wood, and Linda Salemka
Finally, I would like to extend my most sincere appreciation to my husband, Jim, for

his continual support and encouragement.

TABLE OF CONTENTS

INTRODUCTION ..................................... 1
Factors Affecting Chip Quality ......................... 1
Role of Reducing Sugars in Potato Tubers .................. 2
Factors Affecting Reducing Sugar Levels in Potato Tubers ........ 4
Determining Reducing Sugar Levels ...................... 7
Genetic Evaluations ................................ 8
MATERIALS AND METHODS ............................ 12
Progeny ....................................... l3
Analysis-1989 ................................... l3
Analysis-1990 ................................... 14
Parental Material ................................. 14
Statistical Design and Analysis ......................... 15
RESULTS .......................................... 16
1989 Parental Clone Analysis .......................... 16
1990 Clone Analysis ............................... 20
1989 Progeny .................................... 27
1990 Progeny Analysis .............................. 41
Discussion ..................................... 59
Future Research .................................. 63
LITERATURE CITED .................................. 64

iv

TABLE OF CONTENTS

INTRODUCTION ..................................... 1
Factors Affecting Chip Quality ......................... 1
Role of Reducing Sugars in Potato Tubers .................. 2
Factors Affecting Reducing Sugar Levels in Potato Tubers ........ 4
Determining Reducing Sugar Levels ...................... 7
Genetic Evaluations ................................ 8
MATERIALS AND METHODS ............................ 12
Progeny ....................................... 13
Analysis-1989 ................................... 13
Analysis-1990 ................................... 14
Parental Material ................................. 14
Statistical Design and Analysis ......................... 15
RESULTS .......................................... 16
1989 Parental Clone Analysis .......................... 16
1990 Clone Analysis ............................... 20
1989 Progeny .................................... 27
1990 Progeny Analysis .............................. 41
Discussion ..................................... 59
Future Research .................................. 63
LITERATURE CITED .................................. 64

iv

Table 1.
Table 2.
Table 3.
Table 4.
Table 5 .
Table 6.

Table 7.

Table 8.

LIST OF TABLES

Parental Varieties and Traits of Interest .................. 13
Correlations--1989 Parental Material .................... 17
Correlations--1990 Parental Material .................... 22
Correlations-4989 Progeny ......................... 33
Correlations-4990 Progeny ......................... 46
Mean Separations for 1989 Progeny Glucose Content Determined 2 Months
After Harvest .................................. 48
Mean Separations for 1989 Progeny Test Tape Readings Evaluated 5 Months
After Harvest .................................. 49
General (GCA) and Specific Combining Ability (SCA) for Potato Chipping
Quality Characteristics ............................ 60

Figure 1.
Figure 2.
Figure 3.
Figure 4.
Figure 5.
Figure 6.
Figure 7.
Figure 8.
Figure 9.
Figure 10.
Figure 11.
Figure 12.
Figure 13.
Figure 14.

Figure 15.

Figure 16.

Figure 17.

Figure 18.

LIST OF FIGURES

Chip color of 1989 parental material stored at 10C ..........
Glucose level of 1989 parental material stored at 10C ........
Sucrose level of 1989 parental material stored at 10C ........
Glucose-forming-potential of 1989 parental material stored at 10C .
Chip color of 1990 parental material stored at 10C ..........
Glucose content of 1990 parental material stored at 10C .......
Sucrose content of 1990 parental material stored at 10C .......
GFP of 1990 parental material stored at 10C ..............
Average Agtron reading for 1990 parental material stored at 10C
Average color card reading for 1990 parental material stored at 10C
Average glucose content for 1990 parental material stored at 10C
Average sucrose content for 1990 parental material stored at 10C
Average GFP for 1990 parental material stored at 10C ........
Distribution of visually scored chip color for 1989 progeny from
ND860-2 crosses stored 5 months at 10C ................
Distribution of visually scored chip color for 1989 progeny from
Onaway crosses stored 5 months at 10C .................
Distribution of visually scored chip color for 1989 progeny from
Saginaw Gold crosses stored 5 months at 10C .............
Distribution of visually scored chip color for 1989 progeny from
Superior crosses stored 5 months at 10C ................
Distribution of visually scored chip color for 1989 progeny from
Atlantic crosses stored 5 months at 10C .................

vi

32

36

Figure 19.

Figure 20.

Figure 21.

Figure 22.

Figure 23.

Figure 24.

Figure 25.

Figure 26.

Figure 27.

Figure 28.

Figure 29.

Figure 30.

Figure 31.

Distribution of visually scored chip color for 1989 progeny from

each parent averaged over all crosses stored 5 months at 10C . . . 40
Distribution of Agtron chip color for 1990 progeny from

Saginaw Gold stored 2 months at 10C .................. 42
Distribution of Agtron chip color for 1990 progeny from Superior

stored 2 months at 10C ........................... 43
Distribution of Agtron chip color for 1990 progeny from ND860-2

stored 2 months at 10C ........................... 44
Distribution of Agtron chip color for 1990 progeny from each parent
averaged over all crosses stored 2 months at 10C ........... 45
Distribution of Agtron chip color for 1989 progeny from Saginaw Gold
stored 5 months at 10C ........................... 51
Distribution of Agtron chip color for 1989 progeny from Superior

stored 5 months at 10C ........................... 52
Distribution of Agtron chip color for 1989 progeny from ND860-2

stored 5 months at 10C ........................... 53
Distribution of Agtron chip color for 1989 progeny from each parent
averaged over all crosses stored 5 months at 10C ........... 54
Distribution of visually scored chip color for 1990 progeny from

Saginaw Gold crosses stored 5 months at 10C ............. 55
Distribution of visually scored chip color for 1990 progeny from

Superior crosses stored 5 months at 10C ................ 56
Distribution of visually scored chip color for 1990 progeny from
ND860-2 crosses stored 5 months at 10C ................ 57
Distribution of visually scored chip color for 1990 progeny from each
parent averaged over all crosses stored 5 months at 10C ....... 5 8

vii

INTRODUCTION

The potato is a major food crop worldwide and in the United States and is a
valuable source of essential vitamins, minerals, and trace elements (28). Its, protein
content is comparable to other root crops. It is grown in more countries than any crop,
excluding maize, as it adapts well to various climates and growing conditions. It 1983
potatoes ranked fourth, world wide, in acres grown and fifth in monetary crop value
(28, 36). In the United States, over 18 million metric tons are raised annually.

Michigan ranks tenth in the US for potato production1 . There are several regions
of potato production in Michigan, with approximately half of the total acreage and
production in the west central (Montcalm County) and east central thumb area of the
lower peninsula. Michigan potatoes are used for fresh market, seed and processed
products. Approximately 11-12 % of the US crop is utilized by the chip-processing
industry, while 30% of the Michigan crop is used for chip—processing1 .

Factors Affecting Chip Quality

Potatoes for chip processing must meet specific quality standards (11, 43, 53, 54,
61). Factors include consistent yields of mature (ll, 16, 26, 43, 54), medium-sized
(40-65 mm) tubers (26, 54) with a dependable production of light color chips throughout
the processing season (26, 42, 63). A flat, round shape with shallow eyes minimizes
waste during processing (54). Tubers free from external and internal defects (42, 54)
are desired to produce visually appealing chips and to minimize waste. High specific

 

lChase, R. Personal communication.

2
gravity (> 1.080) (27, 42, 43, 54), low sucrose levels (<2.8 mg/g fresh weight) at
harvest and during storage (61), or the ability to achieve low reducing sugar levels (< 2.0
rug/g glucose fresh weight) through reconditioning (11, 13, 18, 24, 33, 35, 40, 57, 62,
63), are required for producing light color chips.

A specific gravity above 1.080 minimizes oil absorption during frying which
increases the shelf life of the product, resulting in higher quality to the consumer and
decreased processing costs (9, 20, 42, 43, 64). Immature tubers tend to have lower
specific gravity than do mature tubers (27 , 42, 43). Several researchers have noted a
correlation between specific gravity and chip color (27, 43, 55 , 56). As the specific
gravity increases, often the chip color improves (27 , 43, 55, 56).

In potato tubers, the primary reducing sugars are glucose and fructose (2, 3, 20,
33, 52). Reducing sugars are produced by the hydrolysis of sucrose (7, 15 , 17, 21, 28,
49, 50). The reducing sugar level is generally considered to be the primary factor
affecting chip color (3, 11, 13, 14, 15, 16, 18, 33, 55, 61). Hughes and Fuller (17)
found that 90% of the variation in chip color could be related to the concentration of
reducing sugars in tubers. High reducing sugar levels result in a dark chip color (9, 30,
60), an undesirable taste (9, 60), and often a poor texture (12, 13, 14, 20, 35). It is
generally accepted that the most important factor to consumers in assessing potato chip
quality is chip color (3, 9, 26, 27, 54, 63).

Role of Reducing Sugars in Potato Tubers

Chip browning is the result of the Maillard reaction, a nonenzymatic process
where the carbonyl group of the monosaccharide reducing sugars (glucose and fructose)
reacts with the amino group of free amino acids during exposure to heat during
processing. This reaction produces brown melanoidin pigments (2, 14, 15 , 16, 20, 39,
41, 44, 48, 50). Carbohydrate metabolism in potatoes is a complex set of events,
mediated by numerous enzymes (12, 15, 21, 28). During the growing season, sucrose

3
is the dominant sugar produced and translocated from the leaves to the developing tuber
tissue (12, 46, 49, 50). Sucrose is important for actively growing and stored tubers (28,
45) serving as an energy and carbon source for starch synthesis (12, 45, 47, 49). Starch
is synthesized from sucrose during tuber growth resulting in a decreasing sucrose rating
(mg sucrose/ g fresh tuber) as tubers reach maturity (12). During storage, especially
when tubers are held under such stress conditions as cold temperatures or poor
ventilation, the starch may break down to sucrose via the enzymes phosphorylase and
sucrose synthetase (12, 45 , 55). This is a reversible reaction when the stress is removed
(2, 12, 22, 23, 34, 45). Invertase is involved in the enzymatic degradation of sucrose
to glucose and fructose (2, 3, 12, 15, 16, 33, 55). A protein inhibitor of invertase
prevents the hydrolysis of sucrose during tuber growth. Invertase becomes active in
storage (2, 33, 47 , 49). Before cold storage, newly harvested mature tubers have low
levels of reducing sugars and total invertase activity and high levels of the invertase
inhibitor (33, 34, 55). Basal invertase activity is non-existent due to excess invertase
inhibitor. During cold storage, starch is converted to reducing sugars ( 12, 46).
Invertase production increases until it reaches a level above that of the inhibitor and basal
invertase activity begins. As the maximum level of reducing sugars is reached, total
invertase levels decrease and basal invertase activity decreases as inhibitor levels rise.
This reaction is reversible at warmer temperatures (34). Senescent sweetening involves
the breakdown of the amyloplast membrane after long-term storage and causes a rapid
and irreversible increase in sucrose levels (12, 22, 49). Schwimmer (38) reported
increased levels of phenols (especially chlorogenic acid) may result in increased reducing
sugar levels due to the inhibition of the enzyme phosphorylase which is involved in

starch synthesis.

4
Factors Affecting Reducing Sugar Leveh in Potato 'hrbers

Numerous factors affect the level of reducing sugars in tubers (11, 20, 24, 40,
41, 42, 50, 63). Cultivar (11, 20, 24, 60), management practices (11, 24),
environmental conditions/ stresses during the growing season (11, 20, 39), maturity level
of the tubers at harvest (20), air temperature at harvest (42, 43), handling of the tubers
after harvest (20, 41 , 48), storage conditions (20, 24, 40) and reconditioning ability are
the factors most often considered (11, 20, 40, 63).

Cultivars vary in their accumulation of starch and total sugars during the growing
season. The ability to reduce their sucrose pool as they reach maturity and to maintain
low reducing sugar levels during storage is cultivar dependent. (20, 46, 49, 55, 63).
Cultivars capable of reaching low sucrose levels before harvest generally process well
from storage at intermediate temperatures of 8.8-11.7C (30, 46). Poor processors
accumulate greater amounts of sucrose at maturity, than do good processors which appear
more efficient at converting sucrose to starch (45, 46). Sucrose serves as a substrate for
reducing sugar production via invertase but does not directly participate in the Maillard
reaction (7 , 16, 46, 50). In poor processors, the rate of reducing sugar production is
greater than the rate of removal for cellular energy needs (46). This results in a rapid
accumulation of reducing sugars in storage. Good processors seem to produce reducing
sugars at a rate close to cellular use rates which results in only a slow accumulation of
reducing sugars over time (46). Sucrose levels of 2.8 mg/g fresh tuber or less at
harvest (12, 46), and a reducing sugar content of 2.0 mg/g fresh tuber or less at
processing (30, 50) will generally produce chips with acceptable color from tubers stored
at intermediate temperatures and in well ventilated conditions (30, 47 , 50).

Management practices that encourage vine growth late in the season tend to delay
tuber maturity which in turn results in elevated reducing sugar levels during storage (37,
42, 55). Early planting is the best means to ensure maturity at harvest (43). High levels

of nitrogen and potassium, particularly late in the season, can delay maturity; while high

5

levels of phosphorous can result in early maturing of the crop (37 , 42). Late season pest
control can delay maturity by delaying vine death. Harvesting as late as feasible gives
the crop time to mature and allows complete translocation of carbohydrates from leaves
to tubers. To prevent cold injury to the tubers, harvest must be finished before air
temperatures fall below 10C (42, 43). Drought conditions longer than three days and
high temperatures during the growing season can also increase reducing sugar
accumulation (33, 40, 42, 43, 57).

Mature tubers are best for chip production when the level of reducing sugars is
generally at the lowest level as genetieally determined for a given variety (45, 46, 50,
52). They also handle, store and recondition better than tubers harvested when immature
(46, 55 , 59). Physical factors such as tuber size, skin set and vine death have not been
adequate predictors of maturity in relation to a tuber’s ability to maintain low reducing
sugar levels during storage (37). Chemical or physiological maturity is defined as when
a tuber attains its maximum specific gravity and its minimum sucrose levels (20, 37, 46,
49). Tubers chipped directly from the field tend to produce acceptable color chips,
regardless of maturity level or other factors (5 , 11, 28). However, even with proper
storage conditions, reducing sugars accumulate and chip color becomes darker faster in
tubers harvested when immature than when mature (5, 28, 55).

Immature tubers have a higher level of sucrose, associated with the rate of sucrose
translocation from the leaves exceeding the rate of conversion to starch in the tuber (49).
This is not accompanied by a higher level of reducing sugars at harvest in immature
versus mature tubers (7 , 28, 30, 49). Immature tubers may produce acceptable chips out
of the field due to the presence of the invertase inhibitor which inhibits the conversion
of sucrose to glucose and fructose (33, 47, 50). However, after storage the chips
, produced are often dark and unacceptable (7, 55).

6

”Reversion" is the phenomenon where tubers that can produce acceptable chips
immediately after harvest will not produce acceptable chips after even a short storage
period (5). This often occurs in tubers harvested when immature (5, 55).

Tubers harvested at air temperatures of 10C or below often have elevated
reducing sugar levels during storage. These tubers will not produce acceptable chips
after storage (42, 43, 55).

Rough handling leads to bruising and an increase in tuber respiration rates with
an increase in sucrose production which serves as a substrate for reducing sugar
production and dark colored chips (41 , 48).

Storage temperature of the tubers plays a major role in reducing sugar
accumulation (2, 11, 13, 20, 26, 30, 33, 40, 43, 60, 63). An intermediate temperature
of 8.9-12.8C results in minimal reducing sugar accumulation and generally permits the
production of acceptable color chips after storage of 3-6 months. At this temperature,
reducing sugar production is close to the rate of use by respiration, but it does result in
sprouting and shrinkage (11, 46, 47). Therefore, the use of sprout inhibitors is required
for long term storage at intermediate temperatures (43). Storage at temperatures of
4.4-6C results in reduced shrinkage due to slowed respiration (2, 8, 26, 51, 64) and
decreased sprouting (2, 3, 26, 51, 64). There is decreased need for sprout inhibitors (8),
decreased costs associated with maintaining storage facilities at higher temperatures (3),
and decreased losses due to diseases transmitted while in storage (2, 14, 51). However,
cold temperatures cause increased starch degradation, which leads to increased sucrose
levels (21 , 33, 46). This elevated sucrose level eventually results in an increase in
reducing sugar levels (2, 11, 12, 13, 26, 30, 35, 40, 43, 55) and dark color chips when
processed (2, 13, 26, 43, 60, 62).

The ability of a tuber to lower reducing sugar levels after storage via
reconditioning is also important (11, 13, 20, 24, 35, 43, 55, 57, 62, 63). Reconditioning
is accomplished by storing tubers at 15.5-21C for varying lengths of time. Varieties

7
differ in their ability to successfully lower their reducing sugar levels to an acceptable
concentration (1 1 , 20, 24, 57, 59, 63). Reconditioning seems most effective for tubers
stored at 4.4-7C. (ll). Tubers stressed during the growing season are difficult to
successfully recondition, as are tubers harvested when immature (20, 59). Ideally, tubers
would be stored at low temperatures (4-6C) and processed without reconditioning to save

expenses and time associated with reconditioning (8, 61).

Determining Reducing Sugar Levels

Numerous methods are used to determine levels of reducing sugars in a tuber
sample (1, 19, 25, 31, 49, 52, 58). Methods frequently reported include the use of
glucose indicator tape, originally designed to test for glucose in the urine of diabetic
patients (1, 19, 31), gas chromatography (58), calorimetric procedures (25) and the
Yellow Springs Instrument (49, 52).

Test-tape is used as a rough guide for lines that would be obviously unacceptable
for chipping (1 , 19). A yellow color indicates negligible amounts of sugar. Increasing
shades of green indicate increasing concentrations of sugar (1).

Chip color is determined by the use of an calorimeter instrument (Agtron) which
measures light reflection from a sample of chips, or by the use of color cards (30).

Sowoldnos developed a sucrose rating method (46, 47, 50) used to predict, at
harvest, how long a given field of potatoes can be stored and still produce acceptable
chips (46, 47 , 50). This calculation ean also be used to monitor the quality of tubers in
storage and allow quick intervention if problems related to changes in sucrose levels are
noted (46, 49). Tubers must be free of disease and defects, intermediate temperatures
of 8.8-12.7C must be provided and the storage must be properly maintained (50). The
sucrose rating does not correlate with chip quality when tubers are stored at cold
temperatures (3.3-7.2C), because the sucrose pool increases above the initial harvest level
due to cold induced starch degradation (46).

8

The sucrose rating is expressed as milligrams of sucrose per gram of tuber (46,
47 , 50). Tubers with a sucrose rating of 1.0-2.8 at harvest should produce acceptable
chips from long-term storage (7-11 mo). Tubers with a sucrose rating above 2. 8 would
produce acceptable chips after short-term storage (0.5-5.3 mo) (46, 47 , 49, 50).
According to Sowokinos (47 , 49, 50), tubers for successful use in chip production should
have a sucrose rating of less than 2.8 when physieal maturity is reached at harvest (47,
49, 50). Theoretically, the higher the sucrose rating at harvest, the faster the reducing
sugars will be produced in storage (47).

In the late 1980’s, Sowokinos (52) proposed the Glucose-Forming-Potential (GFP)
method to screen breeding clones for processing potential. GFP is expressed as umoles
of glucose per pmoles of sucrose. Tubers must be maintained at 9C during storage to
reduce the clone’s endogenous sucrose level to a minimum value between 1.0-4.0 pmoles
of sucrose per gram of tuber. At the same time, glucose levels increase based upon the
genetic tendency of the clone (50). Those clones that should be superior chippers
maintain a GFP between 0.4-1.0 during long-term storage (8 months). Clones with low
sucrose at harvest are not guaranteed to be good chippers after long-term, intermediate
temperature storage. Clones with a low sucrose rating at harvest and a low GFP during
storage seem to have superior gerrnplasm for chip processing. A profile was developed
that related the patterns of GFP and associated uses for the tubers. High GFP (4.0-13.0)
indicates the tubers are best suited for fresh market use, moderate GFP (2.0-4.0)
indieates tubers would be acceptable for the french fry market and a low GFP (0.2-2.0)
indicates tubers acceptable for the chip market (51).

Genetic Evaluations

Work towards development of varieties that accumulate low reducing sugars
during storage includes a cross by Hyde and Walkof in 1962 (18). One seedling, F5208,
reportedly could be stored at 4.4C for 7 months and produce acceptable chips directly

9

from storage. The chip color was only slightly improved by reconditioning for ten days
(18). Researchers have noted the most rapid accumulation of reducing sugars in the
tubers occurs early during storage, and then slows (18, 33). There was only a slight
worsening in chip color after four months of storage (18). In 1970, Lauer and Shaw (24)
produced a single progeny from a cross of S. phureja x USWl (a Kathadin haploid) that
could be stored at 4.4C for 5 weeks and produce acceptable chips without reconditioning
(24).

Cunningham and Stevenson (9) investigated the correlation between progeny chip
color and the chipping ability of the parents, from a given environment, under storage
conditions of 5 .5 C with reconditioning for four weeks at 21-26.6C. Crosses between
good and poor chippers produced progeny that were darker than the best parents in a
continuous range of color (termed ”continuous variation of chip color”). Parents that
produced light colored chips yielded a higher proportion of progeny that produced light
colored chips (4, 9). Researchers believe that parental performance is a reliable
predictor of the mean performance of the progeny and the ability to transmit chip color
is heritable in a given population in a given environment (4, 9, 59). They also believe
environment is as important as cultivar in determining expression of this trait (9, 54, 59,
61).

Johansen and Ehlenfeldt have investigated reducing sugar accumulation during
cold storage (10). They used diallel crosses involving two advanced selections, ND860-2
and ND2221-6 and two standard varieties Norchip and Kennebec. ND860-2 and
ND2221-6 are clones with S. phureja in their pedigree. They exhibit the ability to chip
directly out of cold storage (3-4C), a trait termed ”cold temperature processibility"
(”CTP") (8, 64), which seems related to the ability to accumulate minimal reducing

sugars during cold storage. These clones were able to transmit the "CTP" trait to their

progeny (10)-

10

Ehlenfeldt et a1 (10) found that after 100d of cold storage (3-4C), progeny
families had reducing sugar levels that were more closely distributed toward the value
of the parent with the higher reducing sugar values. Crosses between ND860-2 and
ND2221-6 produced progeny with the lowest reducing sugar levels of all crosses, but
above the levels of either parent. No definite genetic segregation patterns were noted
(10).

ND860-2 was found to have the lowest total sugar levels during growth, at
different stages of maturity and under various time and temperature storage treatments
than other cultivars examined (8). The level of sugars increased during cold storage, but
not enough to cause dark chips when processed. Coffin et al (8) believe the ability to
chip from cold storage is associated with low initial sugar levels rather than a resistance
to cold temperature sweetening. Possible theories are related to differences in enzyme
systems responsible for starch biosynthesis and degradation, differences in the
ultrastructure of the amyloplast membrane (which could affect the accessibility of the
starch-degrading enzymes to the starch in storage) or differences in the starch
composition of the amyloplast (64).

Accatino (4) investigated the inheritance of reversion resistance and reconditioning
ability. In diploids, he found chip color was determined by two loci each for reversion
resistance and reconditioning ability (or possibly common loci). At least one dominant
allele must be present at each loci to produce good chips. In tetraploids he found the
same results-two loci are involved for each trait and at least one dominant allele must be
present at each loci to produce good chip color (4).

Loiselle et al. (26) separated the genetics of chip color into two components.
Chipping stability represents the consistency of chip color produced by a genotype stored
at different conditions. Overall chipping ability represents the average performance of
a genotype over various treatments. The major source of variation seems to be due to

the overall chipping ability component. The researchers determined that general and

11
specific combining ability were both signifieant in both component; thus, additive and
dominant genetic interactions are involved in chipping ability (26).

Finding a line that could be stored at low temperatures and chip directly out of
storage (without reconditioning) would save growers money in energy costs, in decreased
need for sprout inhibitors and in allowing longer storage without loss of quality due to
sprouting, shrinkage and chilling injury (8, 10). The task of improving tuber
processibility can be addressed by the using cultivars known to meet processor

requirements, manipulation of management factors, handling and storage conditions.

MATERIALS AND METHODS

Progeny

Crossing blocks were established in the greenhouse (January-March 1987 and
1988) with seven clones mated in a diallel design. The parental clones used are listed
in Table 1, along with pertinent agronomic characteristics (6).

The field studies were conducted at the Michigan State University Montcalm
Research Farm, Entrican, MI (MRF) and the MSU Clarksville Horticultural Experiment
Station, Clarksville, MI (CHES). Tubers from 1987 crosses and seedlings from 1988
crosses were hand-planted at the Montcalm Research Farm on May 22 and June 3, 1989
respectively. Tubers and seedlings were also planted at the Clarksville Horticultural
Experiment Station on May 23 and June 8, 1989, respectively. Tubers harvested in 1989
from the Clarksville station were stored at 4C and used for seed the following year.
They were planted at the Montcalm Research Farm on May 9, 1990. Standard
management and pest control practices were used throughout the growing season. A total
of 20 tubers and seedlings were planted approximately 3’ apart within rows and 34"
between rows in 20’ plots to insure adequate spacing and prevent mixing during harvest.
Plants were sprayed with a desiccant, two weeks prior to harvest. Tubers were hand
harvested to minimize the risk of mixing progeny and bruising during harvest. Harvest
at the Montcalm Research Farm was on September 28, 1989 (98d and 88d after
planting). The tubers were harvested on October 10, 1989 (110d and 93d after planting)
at the Clarksville station. In 1990, the tubers were harvested at the Montcalm Research
Farm on September 10 and 11 (92d after planting).

l2

13
Table 1. Parental varieties and traits of interest

 

 

Variety Tuber Type-Skin Market Use
Atlantic Round-White Chip—Field-Some Storage
Saginaw Gold Round-Yellow Flesh Chip-Field

Superior Round-White Fresh Market

Onaway Round-White Fresh Market

Lemhi Russet Long-Russet French Fries

Spartan Pearl Round-White Chip-Field

ND860-2 Round-White Chip—Cold Storage

 

Tubers (greater than 2" diameter) from each of the 20 individual hills within a
family were harvested. They were held at 18.4C for two weeks. The tubers from the
Montcalm Research Farm were stored at 10C for two month analysis. The tubers from
the Clarksville Station were stored at 4C for use as 1990 seed material.

Analysis-1989

The extraction procedure was adapted from the work of Dr. J. Sowokinos of the
University of Minnesota. Two months after harvest, two tubers from each progeny hill
were sliced apical to basal end and the center core tissue removed. The tissue was diced
and a random 20 g sample was weighed and mixed with 50 ml distilled water for 60 sec
in a Sorvall blender. The final volume was brought to approximately 80 ml. The extract
was sieved through a coarse sieve and was refrigerated for 1 hour to allow the sediment
to settle. Two-20 ml aliquots of the supernatant were then removed and frozen (—20C)
for later analysis (46, 52).

Five months after harvest, 2 tubers from each hill were sliced from apical to
basal end and two-1/8" slices were removed from each tuber for frying and chip color
determination. Test tape analysis was performed on the remaining tissue using the

glucose strip test (18).

14
Analysis-1990

Two months after harvest and storage at 10C, five tubers per progeny hill were
prepared for sugar analysis as in 1989. Fifty grams of tissue were blended with 80 ml
distilled water. The final volume was approximately 100 ml.

At two and five months after harvest, five tubers from each hill were prepared
for frying as in 1989. With the larger tuber size, four slices per tuber were fried and
chip color determined.

Glucose and sucrose analysis were accomplished by the use of the Yellow Springs
Instrument (Model 2000) (49, 52). Chip color determinations were made visually by the
use of the Potato Chip Color Reference Standards developed by Proctor and Gamble
(PG/SPA color eards) in 1989 and by the Agtron Model E~10 self-calibrating
calorimeter, standardized at the factory, in 1990.

Parental Material

In 1989 seven varieties and advanced breeding lines were evaluated for changes
in glucose and sucrose levels and chip color ratings over time. In 1990, four clones were
evaluated.

Parental varieties were planted by hand. Plots were 20’ long and spacing was 1’
between each seed piece with 3’ between varieties and 34" between rows. Planting dates
were May 22, 1989 and May 5, 1990 at the Montcalm Research Farm and May 23, 1989
at the Clarksville Station. Standard cultural and pest management practices were
maintained throughout the growing season.

Plots were hand harvested on Sept. 28, 1989 (97d after planting) and Sept. 10,
1990 (96d after planting) at the Montealm station and on Oct. 10, 1989 (109d after
planting) at the Clarksville Station. Each variety was bagged and stored at 18.4C for
two weeks, then stored at 10C until analyzed.

15

From the 1989 harvests, varieties were analyzed monthly from 0-6 months after
harvest and in 1990, at 2, 4 and 6 months after harvest.

Ten tubers were removed from storage and a center cut was made from apieal to
basal ends (49, 52). Two slices were removed for frying and chip color evaluation. The
remaining central core tissue from all 10 tubers was diced and mixed for a 200 gram
sample. The tissue was blended with 400 ml distilled water in an Acme Juiceratar. The
extract was refrigerated for 1 hr, two 20 ml aliquots were removed and frozen (-20C)
for analysis at a later time (46, 52, 63).

Glucose and sucrose determinations were made by use of the Yellow Springs
Instrument (Model 2000) (49, 52). Chip color determinations were made by the use of
an Agtron E-10 calorimeter.

Statistical Design and Analysis

The studies were designed as randomized complete blocks. The parental material
in 1989 consisted of 1 replication. In 1990, there were 3 replications. The progeny
study in 1989 had 3 replications. In 1990, there were 2 replications.

In 1989, the diallel analysis for the progeny was based on 20 individual progeny
per replication. In 1990, the diallel analysis was based on 10 individual progeny per
replication.

Data was analyzed using the MSTAT data analysis program. It was transformed
by taking the square root of Y+1/2 for glucose, sucrose rating and glucose-forming-
potential (GFP) due to the presence of zero values in the data file (53). Analysis of
variance was performed with the least significant differences (LSD) determined.
Correlations were determined on the untransformed data. Glucose, sucrose rating,
glucose-forming-potential and chip colors were correlated by individual clones or progeny
and across all the clones or parents in a study. Diallel analysis in the MSTAT program
was performed to determine General and Specific Combining Ability.

RESULTS

1989 Parental Clone Analysis

Seven clones were analyzed in 1989 for changes in glucose levels, sucrose levels,
glucose-farming-patential (GFP), and chip colors (by the Agtron E10 machine) over 6
monthly extraction times. With the Agtron E10 machine, values 60 or above are
acceptable. The clones examined were Atlantic, Superior, Saginaw Gold, Onaway,
Lemhi Russet, and Spartan Pearl. The study was conducted at the Montcalm Research
Farm and the Clarksville Horticultural Experiment Station. The data is discussed with
loeations combined as the results of the analysis indicated no differences due to location.

Tables 2-6 present correlation data for the study. Most of the correlations were
very low (0.1270778). Habib and Brown (14) suggest a correlation above 0.80 has
actual predictive value. In a breeding program such numbers are not expected, but a
statistically significant correlation can be valuable in determining the usefulness of the
data.

Table 2 presents correlations for the 1989 parental material. The glucose level
was significantly negatively correlated with chip colors (by use of the Agtron E10
machine) in 3 of the clones examined (Superior, Saginaw Gold, and Onaway). Sucrose
level was not correlated with glucose level in any clone. Glucose was positively
correlated with GFP in Spartan Pearl, ND860-2, and Saginaw Gold. Sucrose level was
negatively correlated with GFP Spartan Pearl, ND860-2, and Atlantic. Sucrose level did
not correlate with chip colors. Glucose—farming-potential did not correlate well with chip

colors.

16

17
Table 2. Correlations--l989 Parental Material

 

Glucose Sucrose GFP Chip Color

- NS NS NS
“ —0.649* -0.606"I

Glucose
Sucrose
-— NS NS -0.87 **

- NS NS

Glucose
Sucrose
Glucose -- NS —0.67 1* -0.693*
Sucrose

GFP

I -- NS NS
. r , , NS
Glucose - NS NS 0756“
Sucrose -- NS NS
LemhrRusset : . . , ., '
- NS NS NS
l -- NS NS

Glucose
Sucrose
- NS 0.749“ NS
-- -0.70 ** NS

Glucose
Sucrose
GFP , A.
Spartan Pearl . . . . .. _ ;
- -- 0.749" NS

-- -0.627* NS
‘ -- .f ...... NS_._.___, ‘

Glucose
Sucrose
GFP _ p i, , ......
Over AllParental Clanes i . .
Glucose -- -0.227* 0.462" -0.778"'*
Sucrose -- 0298" NS

CLFP -- .Q 559'"

*Significant at 0.05 level
"Significant at 0.01 level

Chip colors were darker in 1989 than would be expected at all storage times
examined. Improper frying technique or improper oil temperature are possible
explanations. The problem seemed to affect all clones equally so general trends can still

18

be observed from the data presented.

In looking at chip color, ND860-2 provided the best chip colors across all storage
periods, whereas Onaway had consistently the poorest chip colors (Fig. 1). Atlantic
readings were generally high, while Saginaw Gold, Lemhi Russet, and Spartan Pearl
were intermediate. There was a slight darkening of chip color observed over storage

periods.

 

AGT RON READ | NG

 

100
*ATLANTI C

'l' ONAWAY

80 ESPARTAN PEARL

60—

+supemon *SAG. GOLD
*Lam a. +naaea-2

 

 

 

—-v
(
..

 

_ ‘T ’

 

20 4—

0 l

’1989

 

M—

l 1 I

October Novenber Decenber January February March

I 1990

STORAGE T l ME

 

figure 1. Chip color of 1989 parental material stored at 10C

 

19
Onaway had the highest glucose levels across all storage periods (Fig. 2), while
ND860-2 and Atlantic had the lowest levels. Spartan Pearl, Lemhi Russet, and Saginaw
Gold again fall between extremes. Superior, Saginaw Gold, and Onaway exhibited a
gradual increase in glucose levels over storage periods, while ND860-2 and Atlantic and
Spartan Pearl stayed fairly constant over time.

 

M3 GLUCOSE/GR TUBER

 

+ATLANTIC +supenlon *SAG. GOLD

 

 

 

 

 

 

October Noven'ber December January February March
1989 | 1990

STORAGE TIME.

 

 

 

Figure 2. Glucose level of 1989 parental material stored at 10C

The sucrose level (Fig. 3) showed a trend towards a gradual decrease over time.
There were no strong varietal trends noted.
The GFP (Fig. 4) showed no strong trends. Atlantic and ND860-2 were stable

over time.

20

 

MG SUCROSE/GR TUBER

 

*ATLANTIC +supenioa *saa. Gate

12 omvar *LEMHI n. +Naeaa-2

 

 

 

 

 

 

I
October Novenber Decenber January February March
1989 | 1990

STORAGE T I ME

 

 

 

Figure 3. Sucrose level of 1989 parental material stored at 10C

1990 Clone Analysis

Atlantic, Superior, Saginaw Gold, and ND860-2 were evaluated for changes in
glucose content, sucrose level, GFP, and chip color (by the use of PG/SFA color cards)
over time. Values 4 or below are acceptable when using the color cards to evaluate chip
color. The study was conducted at the Montcalm Research Farm.

Table 3 presents correlation data for the study. Atlantic and Saginaw Gold did
not have any significant correlations for any variables examined. In ND860-2, a negative
correlation was found between sucrose and glucose levels. Superior produced a
significantly positive correlation between chip color and glucose. Across all clones, chip

color was significantly correlated to glucose levels.

21

 

GLUCOSEISUCROSE RATIO (GFP)

 

*ATLANTIC +supea|on *SAG. GOLD
9° T"Grammar *Laa-u n. +maea-2

* SPARTAN PEARL

60—

 

 

 

 

 

October Novenber December January February March
1989 l 1990

STORAGE TIME

 

 

 

Figure 4. Glucose-forming-potential of 1989 parental material stared at 10C

In looking at general trends, ND860-2 provided the best chip colors over time,
using the PG/SFA color cards. The Atlantic sample in January was poor, but improved
in March. Saginaw Gold and Superior had the poorest overall chip colors (Fig. 5). The
glucose level increased gradually over time. ND860-2 was consistently lowest, while
Superior was consistently the highest (Fig. 6). The sucrose level showed a general
increase over storage period for all varieties except Saginaw Gold which decreased in
March. ND860-2 had the highest sucrose level followed by Atlantic and Superior
(Fig. 7). The GFP did not exhibit obvious trends over storage time (Fig. 8).

Analysis of variance was performed for chip color (by Agtron E10 and PG/SFA
color cards), glucose levels, sucrose levels, and GFP. The means were separated by
LSDs as indicated (Fig. 9-13).

22

Table 3. Correlations-1990 Parental Material

 

Glucose Sucrose GFP Chip Color
Glucose -- NS NS NS
Sucrose - NS NS
GFP ..... w ‘ -- ' NS M
Glucose - NS NS NS
Sucrose -- NS NS
Glucose - NS NS 0747*
Sucrose -- NS NS
GFP ,w A! . '7' NS.
Glucose - NS NS NS
Sucrose -- -0.718* NS
GFP . -- NS
iiiQW'AIlParemlem - ‘ . y
Glucose - NS NS 0.468“
Sucrose -- NS NS
GFP -- NS

 

 

 

 

 

 

*Significant at 0.05 level
"Significant at 0.01 level

23

 

 

 

 

 

 

 

 

 

PG/SFA COLOR CARD READING
10
"'ATLANTIC '+'SAGINAw GOLD
* SUPERIOR + NDBBO- 2
8 '— 4
5*- _
I
4 u—
2 I—
0 l
Noven'ber January March
1990 | 1991
STORAGE TIME

 

 

 

Figure 5. Chip color of 1990 parental material stored at 10C

24

 

MG GLUCOSE/GR TUBER

 

2.5

1.5"—

 

“"ATLANTIC +SAG. GOLD *supERIOR +Naaaa-2

 

 

 

 

November January
1990 l 1991

STORAGE TIME

 

 

 

Figure 6. Glucose content of 1990 parental material stored at 10C

 

25

 

MG SUCROSE/GR TUBER

 

1.4

1.2—

0.8"

 

:“ATLANTIC +SAG. GOLD *SUPERIOR +Noasa—2

 

 

0 1
November January

STORAGE TIME

 

March
1991

 

Figure 7. Sucrose content of 1990 parental material stored at 10C

 

26

 

GLUCOSEISUCROSE RATIO (GFP)

 

25

‘°‘ ATLANTIC + SAG. GOLD * SUPERIOR + NDBBO- 2

 

 

 

 

 

 

November January March
1990 | 1991

STORAGE TIME

 

 

 

figure 8. GFP of 1990 parental material stored at 10C

27

The chip color ratings (based on the use of the Agtron E10 machine) showed no
significant differences at the November storage time; however, in January, ND860-2 was
significantly better than all other clones (Fig. 9). The chip color, as determined by the
PG/SFA color cards was not significantly different in November (Fig. 10). In January,
ND860-2 chip colors were significantly better than all others. In March, Atlantic and
ND860-2 chip colors were significantly better than Superior. Saginaw Gold was not
significantly different than the other clones.

The glucose content of the parents was not significantly different in November
(Fig. 11). In January, Superior had significantly higher glucose levels than ND860-2;
however, Atlantic and Saginaw Gold levels were intermediate, but not significantly
different from either ND860-2 or Superior. In March, Superior still contained the
highest glucose level, ND860-2 and Atlantic had the lowest levels while the Saginaw
Gold level was intermediate. The sucrose levels were not significantly different in
November or March (Fig. 12). In January, Atlantic and ND860-2 had significantly
higher levels than Superior, but not Saginaw Gold. The GFP showed no significant
differences at any storage period (Fig. 13).

1989 Progeny

A half diallel mating design was produced using Atlantic, Superior, Saginaw
Gold, Onaway, and ND860—2 as parents. The resulting progeny were analyzed for
glucose level, sucrose level, GFP, and 5-month chip color determination (by use of the
PG/SFA color cards) and test-tape analysis.

Table 4 presents correlations for the study. Test-tape, chip color ratings, and
glucose levels were all significantly correlated for all the progeny regardless of the parent
and when all the progeny were analyzed together.

28

 

AVERAGE AGTRON READING

 

    

 

 

 

1 0° I Macao-2 IEUPERIOR I SAG.GOLD I ATLANTIC
ao —
AB AB B A
so —
so —
20 —
NOVEMBER JANUARY
| 1990 | 1991 |

STORAGE TIME

“mu-mummumwmmmmmumm m

 

 

 

Figure 9. Average Agtron reading for 1990 parental material stored at 10C

29

 

 

 

     

 

 

AVERAGE PGISFA COLOR CARD READING
1 4 I Macao-2 iSUPERIOR rSAGGOLD IATLANTIc
1 2 -
1 0 -
A
I _
5 _
0 g . [fl 3
NOVEMBER JANUARY MARCH
| 1990 | 1991 |
STORAGE TIME
“mammfiumeuWMNIs-w level.

 

 

 

Figure 10. Average color card reading for 1990 parental material stored at 10C

30

 

AVERAGE MG GLUCOSE/G TUBER
INDaao-z iSUPERlOR ism-sow I ATLANTIC

 

 

 

   

 

 

,9 III/I’l/V/éWA/Zy/II 2,
'., {I .17" , ,’

/. ../

X ,, ;' , /

} '//‘,‘;/l

’ I
./

/

 

Noveuaen JANUARY MARCH
| 1990 | 1991 |

STORAGE TIME

Manama-unnumbermmwmumusm

 

 

 

 

Figure 11. Average glucose content for 1990 parental material stored at 10C

31

 

MG SUCROSE/G TUBER

 

 

 

    

 

 

   

3 A-
fiasco-2 I suPEIuorTI SAGGOLD IATLANTIc
2.5 —
2 I—
1.5 — A
A
I r
o .
NOVEMBER JANUARY MARCH
| 1990 | 1991 I
STORAGE TIME

“mammmuuw-ommmmuuaosm

 

 

 

Figure 12. Average sucrose content for 1990 parental material stored at 10C

32

 

AVERAGE GLUCOSE:SUCROSE RATIO (GFP)

 

 

    

5 [Nessa-2 EUPERIOR ISAGGoLD IATLANTIc
4 _

3 ._ A

2 _

1 F

 

 

 

NOVEMBER JANUARY MARCH
| 1990 | 1991 |

STORAGE TIME

“MamumuWWm-uwmuumm

 

 

 

Figure 13. Average GFP for 1990 parental material stored at 10C

33

Table 4. Correlations--l989 Progeny

 

Jan. chip color

Glucose Sucrose

GFP

Test Tape

(PC/SPA)

 

 

 

 

 

Test Tape

 

flan“:92;:14;?;iis§§§i;9;:%i¥;f-i521}:ff:-¥ii~I:}§:*?9153-5?3:25.»,
. , ‘ ...._.‘,._..,......IO..419“

-0.379**

—0. 194*

NS

-0.280*"‘

NS

-0. 186"

NS
NS

-0.196*
0.249"

NS
NS

0.361** f .; ? ,jjj;

NS
NS

NS
NS

-0. 127"
0.161"

NS
0.276"

1.949.25'7"... ,

-0.240"""
0.287“

_ _9+71._°7".‘,,.,_

NS
NS

,. 4,,IQ-51?_"5'.".. .

NS
0.251"

,_ ., .0503'55W ,

NS
NS

< 9:5??? .. _

-o.154**
0.218"
0.664"

 

*Significant at the 0.05 level
"Significant at the 0.01 level

34

 

PERCENT OF SAMPLES

100 r
=ATLANT I C SUPERIOR I SAG. GOLD

 

90 ONAWAY - NDBED- 2
80 —

7D
50
50
4D
3D
20

1D

 

 

 

0

5-6 6-7 7-8 8-9 >9

PG/ SFA CDLOR CARD READING

1989

 

 

 

Figure 14. Distribution of visually scored chip color for 1989 progeny from ND860—2
crosses stored 5 months at 10C.

35

Analysis of variance was performed for test-tape and glucose level and means
separated by LSDs as indicated. The test-tape value and glucose level had significant
differences as presented in Tables 6 and 7.

A closer look at chip colors (by use of PG/SFA color cards) after 5 months of
storage shows the following. Crosses involving ND860—2 produced progeny with a wide
range of chip colors (Fig. 14). Progeny from ND860-2 self-pollinated (ND860-2
”selfed") were evenly distributed over the range of chip colors (5-9). ND860-2 x
Atlantic progeny demonstrated slightly improved chip color distribution over ND860-2
”selfed" . ND860-2 x Onaway had the poorest distribution of chip colors (primarily
> 9.0).

Most of the progeny resulting from Onaway crosses produced very poor chip
color (Fig. 15). Onaway ”selfed" progeny were the poorest of all the Onaway crosses.
Slight improvements in chip colors were found in crosses with Atlantic, ND860-2, and
Saginaw Gold. Most progeny were consistently very poor (9.0 or above). Saginaw Gold
progeny provided a range of chip colors; however, a majority of the progeny were poor
' (Fig. 16). The poorest chip colors were a result of the crosses Saginaw Gold x Superior
and Saginaw Gold x Onaway. Some improvement in chip colors was seen in progeny
from Saginaw Gold x Atlantic and Saginaw Gold x ND860—2.

Superior progeny provided a range of chip colors, some of which were more
acceptable than was found when other varieties were used as parents, but large numbers
of progeny were associated with poor chip colors (Fig. 17). Superior x Onaway and
Superior x Saginaw Gold progeny were generally 9.0 or above. An improvement in chip
color was seen in progeny from Superior x Atlantic and Superior 'selfed".

Atlantic progeny were evenly distributed across the range of chip colors (Fig. 18).
Atlantic "selfed" progeny produced an even range of chip colors from poor to acceptable.
Atlantic x Onaway progeny had the poorest chip colors. Progeny from Atlantic x
ND860-2 provided some good chip colors.

36

 

PERCENT OF SAMPLES

 

 

 

100
ATLANTIC ‘SUPERIOR .SAG. GOLD

90
ONAWAY . NDBBD- 2

J
.1:
/
.‘l’
’32;
/ /
’I
1"
IA//
I /
'1",
I
/./
I
,
.,//
//
4
I I
,.
7,.
7
/,I
yé
o"/
7,,
/ "

\\\\\‘~\:Q‘\\ ;‘\\\.\ \\\\ \
\\‘\ I\§\\ \
\\\\\\ \\‘ . \ \

\ $79.5 \\§}\V \\§.\
‘ \ .1‘.§¥.§\\\\\\N\\§.

 

 

 

5-6 6-7 7-8 8-9 >9

PG/SFA COLOR CARD READING

 

1989

 

 

Figure 15. Distribution of visually scored chip color for 1989 progeny from Onaway
crosses stored 5 months at 10C.

37

 

PERCENT OF SAMPLES

ELANTIC 'SUPERIOR 'SAG. GOLD
0

NAWAY I NDBSD— 2

 

 

100
90

 

80—

 

 

 

5-6 ' 6-7 7-8 8-9 >9

PG/SFA COLOR CARD READING

1989

 

 

 

Figure 16. Distribution of visually scored chip color for 1989 progeny from Saginaw
Gold crosses stored 5 months at 10C.

38

 

PERCENT OF SAMPLES

 

 

 

 

100
ATLANTIC 'SUPERIOR 'SAG. GOLD
so
ONAwAY INDaso-a
so r-
70

so
so
40
30
20
10

 

 

 

0

5-6 6-7 7-8 8-9 >9

PG/SFA COLOR CARD READING

 

 

1989

 

Figure 17. Distribution of visually scored chip color for 1989 progeny from Superior
crosses stored 5 months at 10C.

39

 

PERCENT OF SAMPLES

100
:ATLANT I C ‘SUPERIOR iSAG. GOLD

 

90 ONAWAY I NDBSO— 2
80 "

70 _

50
SO
40
30
20

1O

 

 

 

0

5-6 6-7 7-8 8-9 >9

PG/SFA COLOR CARD READING

 

1989

 

 

Figure 18. Distribution of visually scored chip color for 1989 progeny from Atlantic
crosses stored 5 months at 10C.

 

PERCENT OF SAMPLES

 

 

'IDU
ATLANTIC ‘SUPERIOR 'SAG. GOLD

90

 

ONAWAY I NDBBD— 2
80 _

70
60
SD
40
30
20
1 0

 

 

 

0

5-6 6-7 7-8 8-9 >9

PG/ SFA COLOR CARD READING

 

 

1989

 

Figure 19. Distribution of visually scored chip color for 1989 progeny from each parent
averaged over all crosses stored 5 months at 10C.

41
When all crosses were analyzed together (Fig. 19), Atlantic produced the highest
proportion of acceptable progeny chip color, followed by ND860-2. Onaway progeny
produced the highest pr0portion of poor chip colors.

1990 Progeny Analysis

In 1990, a half diallel mating design was produced using Saginaw Gold, Superior,
and ND860-2. The resulting progeny were analyzed for glucose content, sucrose level,
GFP, and at 2 and 5 months after harvest, chip color was evaluated by use of the Agtron
E10 machine and PG/SFA color cards.

Table 5 presents correlation data for the study. January chip color evaluation
methods were significantly correlated for PG/SFA color card numbers and Agtron E10
values. There was a great deal of variability in the other correlations. Generally,
glucose levels were significantly correlated with chip color, regardless of the method
used or when evaluated.

An analysis of variance was performed on glucose content, sucrose level, GFP,
and chip color. No significant treatment effects were noted for any of the variables.

General trends for chip colors (by Agtron E-lO reading) at 2 months after harvest
indicated that most crosses produced acceptable progeny at this time. Saginaw Gold
crosses gave progeny with mostly acceptable chip colors, Saginaw Gold X Superior gave
the highest proportion of Agtron readings below 60 (unacceptable) (Fig. 20). Progeny
from Superior crosses also produced mostly acceptable chip colors (Fig. 21). Poor
Agtron readings were found in progeny from all crosses with Superior. Superior
”selfed" progeny produced the highest percentage of Agtron readings above 60.
ND860-2 crosses produced progeny with mostly acceptable chip colors (Fig. 22). The
poorest chip colors for ND860-2 progeny were from ND860-2 x Superior. An analysis
across all the progeny showed most of the crosses produced progeny that yielded
acceptable chip colors after 2 months of storage (Fig. 23).

42

 

PERCENT OF SAMPLES

 

 

 

100 .SAG. GOLD 'SUPERIOR INDEED-2

90

50—
50"
4D—
30"
20—

 

 

 

0—'. s‘

40-44 45—49 50-54 55-59 60-64 65-69 >70

AGT RON READ | INKS

 

 

1990

 

figure 20. Distribution of Agtron chip color for 1990 progeny from Saginaw Gold
stored 2 months at 10C

43

 

PERCENT OF SAMPLES

 

 

 

mo .SAG. GOLD 'SUPERIOR “0350-2
so -
ea -
70 L-
60 -

 

 

 

40-44 45-49 50-54 55-59 60-64 65-69 >70

AGTRON READING

 

1990

 

 

figure 21. Distribution of Agtron chip color for 1990 progeny from Superior stored 2
months at 10C

 

PERCENT OF SAMPLES

 

100 .SAG. GOLD EUPERIOR INDasO—z
so -

ao -
70 P
so _
so -
40 -
90 -
20 -
1D "

0 l I I

40-44 45-49 50-54 55-59 60-64 65-69 >70

 

 

 

AGTRON READING

 

1990

 

 

figure 22. Distribution of Agtron chip color for 1990 progeny from ND860-2 stored
2 months at 10C

45

 

PERCENT OF SAMPLES

 

 

100 iSAG. GOLD 'SUPERIOR 1NDBBU-2
90 ‘
80 ”
7U “
60 ‘
50 ’
4U
30
20

’IU

 

 

 

40-44 45-49 50-54 55-59 60-54 65-69 >70

AGTRON READING

1990

 

 

 

Figure 23. Distribution of Agtron chip color for 1990 progeny from each parent
averaged over all crosses stored 2 months at 10C

46

:90?

m2
m2
m2

«amNd

*ivmfidt

m2
m2
m2

.3396

m2
m2
soomd

3.9.00.

m2
m2
m2

smfimd.

m2
* 3N6
*nmmmd:

m2
m2

...nen.c.

wz
m2

m2

xivovd

LuaNd.

m2

:8 85?.
.860 .50 :3.

2m :83

830 3:0 52

.50
8805
8820

. Seaman!“ . , r, m“ we...”

, ‘ em. 52 _
860 e5 5:

2m cob?

.880 QED 52

~50
9.985

9.329

 

“28 Eng .53.

“28 E5 .5:

~28 £5 .52

8805

 

>585 82 :232280 .n 0:3

3,2 85 as a assuage...
E2 nod 2: a 28%»?

 

47

2m 25%..
sin? -- .28 e5 5.

Sm Se?
m2 m2 -- .28 .56 52

m2 m2 m2 -- .56
m2 m2 m2 wz -- 388m

*swaNd seohmd. ismmnd. m2 m2 -- 8820

8:358 Ewen =<  
e . . _   _ 2m :32.
En? -- 830 95 52

2m 8:?
m2 m2 -- .53 e5 82

m2 m2 m2 -- n30
*Smd 3..an? m2 m2 -- 9.83m
1.3.: m2 m2 m2 m2 m2 089:0

 

§

.983 n 2.3

48

Table 6. Mean separations for 1989 progeny glucose content determined 2
months after harvest.

ND860-2 x Onaway
Atlantic x Saginaw Gold
Saginaw Gold x Onaway
Atlantic X

N D860-2 X

Onaway X

Atlantic x Onaway
Atlantic x ND860—2
Saginaw Gold X

Atlantic x Superior
Saginaw Gold x Superior
Superior X

Saginaw Gold x ND860-2
Superior x Onaway
Superior x ND860-2

wwwwwé駧§§§§§>

Varieties followed by the same letter are not significantly different according
to Fisher’s protected LSD at the 0.01 level.

49

Table 7. Mean separations for 1989 progeny test tape readings evaluated
5 months after harvest.

Atlantic x Saginaw Gold A
ND860-2 x Onaway A
Saginaw Gold x Onaway AB
Atlantic X ABC
Onaway X ABC
ND860-2 X ABC
Atlantic x ND860-2 ABC
Atlantic x Onaway ABC
Atlantic x Superior ABC
Saginaw Gold X ABC
Superior X ABC
Saginaw Gold x ND860-2 BC
Saginaw Gold x Superior BC
Superior x Onaway BC
Superior x ND860-2 C

Varieties followed by the same letter are not significantly different according
to Fisher’s protected LSD at the 0.01 level. ,

50

General trends for chip colors (by Agtron E-lO reading) 5 months after harvest
showed that the progeny range produced a general worsening of chip colors and a greater
percentage of unacceptable chip colors. Saginaw Gold crosses produced a wide range
of chip colors (Fig. 24). The poorest results were from Saginaw Gold x Superior and
Saginaw Gold x ND860-2 crosses. The best progeny were associated with Saginaw Gold
"selfed" crosses. Progeny from Superior crosses had a wide range of chip colors
(Fig. 25). The poorest chip colors resulted from crosses with Saginaw Gold. The best
results were from crosses with ND860-2. Crosses with ND860-2 gave progeny that
covered a wide range of chip colors (Fig. 26). The poorest chip colors were associated
with the progeny from ND860-2 x Saginaw Gold. The best progeny colors were evenly
distributed between ND860-2 x Superior and ND860-2 "selfed" . The progeny from each
parent analyzed together, showed a general decrease in chip colors with a greater range
of chip colors produced, as compared to the results at 2 months (Fig. 27).

General trends for chip color (measured visually by PG/SFA color cards) 5
months after harvest showed the progeny results as follows. Saginaw Gold "selfed'
crosses produced the highest percentage of good chip colors, as well as the some of the
poorest (Fig. 28). Superior crosses provided progeny with a wide range of chip colors,
Superior x ND860—2 crosses produced the highest percentage of good chip colors
(Fig. 29). ND860-2 crosses produced progeny with a wide range of chip colors
(Fig. 30). All ND860-2 crosses produced a high percentage of acceptable progeny.
When the progeny from each parent was analyzed together, there was a fairly comparable

distribution of chip colors regardless of the parent, most of the chip colors in the 3-5

range (Fig. 31).

51

 

PERCENT OF SAMPLES

 

 

100 m. GOLD .SUPERIOR INDEED-2
90 ’
80 '
70 '
60 '
50
40
30
20

10

 

 

 

40-44 45-49 50-54 55-59 50-54 65-69 >70

AGT RON READ | MS

1990

 

 

 

Figure 24. Distribution of Agtron chip color for 1990 progeny from Saginaw Gold
stored 5 months at 10C.

52

 

PERCENT OF SAMPLES

100 ii
FAG. GOLD SUPERIOR iNDBBD-2

90

 

 

 

80‘
70‘
60“
50”
40‘
3D"
2D”

10"

 

 

 

40-44 45—49 50-54 55-59 60-54 65-69 >70

AGTRON READ | M35

1990

 

 

 

Figure 25 . Distribution of Agtron chip color for 1990 progeny from Superior stored 5
months at 10C.

53

 

PERCENT OF SAMPLES

 

 

100

 

SAG. GOLD iSUPERIOR 1ND860-2
90 ”’

80 "
70 ”
60 "
50 ‘
40
30
2O

1O

 

 

 

40-44 45-49 50-54 55-59 60-64 65-69 >70

AGTRON READING

1990

 

 

 

Figure 26. Distribution of Agtron chip color for 1990 progeny from ND860-2 stored
5 months at 10C.

 

54

 

PERCENT OF SAMPLES

 

 

100 'SAG. GOLD ‘supemon .NOBSO-z
so *-

80 —
70 -
so r
50 r-
40 -
30 -
20 -

10“

 

 

 

40-44 45-49 50-54 55-59 60-64 65-69 >70
AGTRON READIm

 

 

1990

 

Figure 27 . Distribution of Agtron chip color for 1990 progeny from each parent
averaged over all crosses stored 5 months at 10C

55

 

PERCENT OF SAMPLES

 

 

 

100 .SAG. GOLD .supemon INDEED-2
so -

an -
70 -
so
50
40
30
20

’IO

 

 

 

0

3—4 4—5 5-6 6-7 7-9 9-9

PG/SFA COLOR CARD READING

1990

 

 

 

Figure 28. Distribution of visually scored chip color for 1990 progeny from Saginaw
Gold crosses stored 5 months at 10C

56

 

PERCENT OF SAMPLES

100 iSAG. GOLD iSUPERIOR INDBBO-2
90 I‘

 

80 ’
70 "
60 ”
50
4O
30
20

10

 

 

 

3-4 4-5 5-6 s7 7—8 8—9

PG/SFA (DLOR CARD READINS

1990

 

 

 

Figure 29. Distribution of visually scored chip color for 1990 progeny from Superior
crosses stored 5 months at 10C

57

 

PERCENT OF SAMPLES

 

 

100 SAG. GOLD iSUPERIOR IND860-2
90 ‘
80 ’
70 ‘
50 ”
50 ’
4D
30
2O

10

 

 

 

}4 4-5 5-5 5-7 7—8 8—9

PG/ SEA COLOR CARD READING

1990

 

 

 

Figure 30. Distribution of visually scored chip color for 1990 progeny from ND860-2
crosses stored 5 months at 10C

58

 

 

 

 

 

 

PERCENT OF SAMPLES
100

.SAG. GOLD tsupemon ‘NDBBO—Z
90 E
80 E
70 I-
50 -
5O -
40 _
20 ;//
10

0 ,
3-4 4—5 5-6 6-7 7-e 8-9
96/ SFA COLOR CARD READING
1990

 

 

 

figure 31. Distribution of visually scored chip color for 1990 progeny from each parent
averaged over all crosses stored 5 months at 10C

59
Discussion

Sugar content and thus chip color is highly subject to environmental factors and
varies from year to year and by location; however, those that are the best processors
overall are generally a good processor in any given year (50). This could account for
some of the variability of our data as compared to what would be expected from work
done by others.

Results seem to indicate that Atlantic and ND860-2 possess the ability to improve
the chipping potential of most crosses. These clones are used as chip-processors and are
able to attain chemical maturity at physical maturity (6). Onaway has the greatest
potential to result in poor chip processing ability. Onaway is strictly a fresh market
potato and is not used for the chip processing market due to excess levels of sucrose at
physieal maturity (6).

ND860-2 is reported to be tolerate cold temperature storage (4C) for as long as
5 months and still produce acceptable color chips without reconditioning (8, 10, 64). ’
From 10C storage, Atlantic and its progeny produced chip color as good or better than
ND860—2 and its progeny. Cold storage may have provided the ability to better
discriminate for improved chip color from ND860-2 than the others.

General combining ability was significant at the 0.05 level for all progeny for all
traits examined, except the November and January agtron readings for the 1990 progeny
(Table 8). This suggests that additive gene action is the primary factor influencing chip
color (32). Therefore, breeding progress can be made through simple recurrent
selection.

Specific combining ability was not significant for any traits of any progeny. This
suggests no one cross was unusually good or poor and is an indicator of the lack of
dominance and epistasis in chip color development (32).

The test-tape method for chip color evaluation is a quick test based on glucose

levels in tuber tissue (1 , 19). As the test-tape value increases, the level of glucose

Table 8. General (GCA) and specific combining ability (SCA) for potato chipping
quality characteristics.

 

 

 

Level of Significance
Year Measurement SCA GCA
1989 Test-tape NS **
Chip color (PG/SPA) NS **
Glucose content NS **
Sucrose content NS **
GFP NS an.
1990 Nov. chip color (Agtron E-lO) NS NS
Jan. chip color (Agtron E—lO) NS NS
Jan. chip color (PG/SPA) NS NS
Glucose content NS **
Sucrose content NS **
GFP NS an:

 

NS--Not significant at the 0.05 level
*--Significant at the 0.05 level
**--Significant at the 0.01 level

61
increases in the tissue. A positive correlation would be expected between test-tape and
glucose, and our results confirm that correlation.

Chip color is largely determined by glucose levels in the tissue being fried (l3,
14, 39, 50). As glucose levels increase, the resulting chip color becomes darker (13, 14,
39) . A significant correlation between chip color and glucose levels would be expected.
Generally, our data produced those same results. A negative correlation resulted when
using the Agtron E10 machine (as glucose levels increased, the Agtron readings
decreased). A positive correlation resulted when using the PG/SFA color cards (as
glucose levels increased, the color card readings increased). A correlation between chip
color and test-tape values would also be expected. Our data indicated that as chip colors
worsened, the test tape values increased.

Chip color evaluations taken at different storage periods may not be expected to
correlate well with one another. Our data did not indicate any correlation between the
November and January progeny chip color results. The chip colors are an indication of
glucose levels at a given time in storage and not necessarily related to glucose levels at
a later time in storage.

Different chip color evaluation methods (i.e. , Agtron E10 and the color cards)
performed at the same storage period would be expected to correlate well as they are
both measuring the glucose levels found in tuber tissue at a fixed storage period. A
negative correlation was found for the January progeny chip color results determined by
the use of the color cards as compared to the results from Agtron E10 machine. This
is as expected, higher Agtron numbers and lower PG/SFA color card numbers are both
indicative of improving chip color.

Sucrose does not directly participate in the reaction that results in the production
of dark color chips during frying (7, 16, 46, 50). It would not be expected to see a
correlation between sucrose levels and chip colors or other factors at a given storage

period (6, 39). Our data found no signifieant correlation for the sucrose levels as

62
compared to the chip colors when the parental material was analyzed. Sucrose levels at
harvest should correlate with chip colors later in storage (46, 47, 50). Our sucrose
analysis was done two months after harvest and the results may not be expected to be
useful for determining later chip color. This could account for the lack of correlation
between sucrose levels and later chip color ratings.

The combination of low sucrose and low glucose levels is termed "chemieal
maturity" (49). A variety that does not reach chemical maturity, such as Onaway or
Lemhi Russet, before it reaches physical maturity is not suited for storage and use as a
chip-processing variety (47, 49, 50, 52). These varieties may produce acceptable color
chips from the field as our data indicate.

Clones with high GFP (> 4), such as Onaway, are best suited for fresh market
uses, moderate GFP levels (2-4), such as Lemhi Russet, are often used for the french fry
market, while those with the best chipping potential have a GFP level less than 2, such
as Atlantic and ND860-2 (53). Our results regarding the GFP were inconclusive.

The analyses performed for these studies demonstrated the value of different
methods for determining chip-processability. Not all methods would be appropriate for
all stages of a breeding program, such as at Michigan State University.

The test tape analysis would be very useful early in a breeding program, for
example at the single-hill evaluation stage. It ean be done quickly and requires only one
tuber for analysis. These factors are both important early in a breeding program when
large numbers of progeny are being evaluated and the number of tubers is relatively
limited.

Frying, with chip color determinations, is useful as it gives the most obvious
answer regarding a progeny’s chip-processing ability at a given time. Due to the
increased time, labor, and tuber numbers required to do an adequate evaluation, this
method is best used when the number of lines being evaluated in a breeding program is

63
significantly decreased. In the MSU program, this would occur at the 8-hi11 stage, about
3 years into the cycle and at the single-hill stage if numbers are not too large (> 1000).
The Yellow Springs Instrument (Y SI) requires the greatest investment in time,
labor, and expense. This method may be best used when a given progeny has been
shown to be a good chip-processor when grown over years and locations. This method
is useful in determining chip-processing ability after long-terrn storage. It is also useful

for a grower to evaluate the chip-processing status of a given lot of potatoes.

Future Research

Follow-up research to this project could investigate variety comparisons of test
tape values and chip-processing ability after various storage periods at 4.4 CH .2 C/ 10 C
with and without re-conditioning.

Standard chip-processing varieties, non-chip-processing varieties, and those known
to possess cold-temperatureprocessability should be considered as parental material to
provide a wide genetic base. The construction of a half-diallel mating pattern, using the

same parents would provide valuable information on the segregation of traits associated

with chip-processability.

 

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