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COLD TEST (BERMINATEON 053
HYBRED SEED CORN

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This is to certify that the

thesis entitled

COLD T3789? GERMIIIATI ”)N
OF
EYPRID SEED CURE

presented by

Gerard Hep tune

has been accepted towards fulfillment
of the requirements for

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COLD TEST GERMINATION OF HYBRID SEED CORN

BY

GERARD NEPTUNE

A THESIS

Submitted to the School of Graduate Studies of Michigan
State College of Agriculture and Applied Science
in partial fulfillment of the requirements
for the degree of

MASTER OF SCIENCE

Department of Farm CrOps

1951

TH Eéls

 

ACKNOWLEDGMENTS

The writer wishes to express his sincere thanks to Dr.
E. C. Rossman for his guidance and appreciable help through—
out the experiments and preparation of this thesis.

He also deeply appreciates the financial support of the
Institute of International Education and the scholarship provided

by Michigan State College for the present year which made it

possible for him to complete this investigation.

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path). ‘3 r}:

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TABLE OF CONTENTS

Introduction

Review of Literature

Materials and Methods

Experimental Results and Discussion
Summary

Literature Cited

Page

24

26

INTRODUC TION

Wherever corn is grown a good stand is essential for
maximum yields. In the northern areas, particularly, obtain-
ing a good stand of corn is often a problem. Cold, wet weather
frequently occurs after planting. Under these conditions, seed-—
ling blights and rots are likely to deveIOp and kill the seedling
before or after emergence. Since the number of plants per
acre has a very large effect on the yield of grain (17), it is
important to understand the factors that influence stands of
corn.

The purposes of this study were to determine:

.(a) the extent of the difference in cold test germination
among the various hybrids grown by Michigan farmers;

(b) the differences that might occur among different
.seed producers of the same hybrid; and

(c) the effect of age of seed on cold test germination.

REVIEW OF LITERATURE

Several factors affecting stands of corn under adverse
conditions have been investigated. Various microorganisms
have been shown to cause reduction in stands of corn under
cold wet conditions (3, 7, 8, 9, 19). Low temperature and
excessive soil moisture have been shown to be favorable for
deveIOpment of various pathogens which attack the seed and
young seedling. Pythiurn fl. have been reported to be the
principal pathogens involved (7, 8). Injury to germination and
seedling vigor was found to be greater as the water content of
the soil increased in cold weather (5). rGermination was not
greatly affected when soil at 30—40% of its water—holding ca—
pacity was inoculated with Pythium.

The amount and the type of seed coat injury have been
shown to cause reductions in stands of corn (1, 2., 10, ll, 12,
14, 20, 21). Injury to the pericarp permits invasion by seed-
borne and soil—borne organisms which cause kernel rot, seed-
ling blight, and root rot. Significant correlations of field
stands with cold test germination have been reported by Tatum

and Zuber (21), and Pinnel (15).

Genetic differences in reaction to attack by seedling
blight organisms have been reported (4, 6, 13, 15, 20). Ge—
netic constitution of the seed was shown to affect cold test
performance with wide differences existing among inbred lines
and hybrids (15, 21). These differences were largely mater—
nal; the pollen parent exerted relatively little influence on the
cold test reaction of the seed.

Commercial processing was found to cause much dam—
age to hybrid seed corn (22). Injury increased as processing
progressed through successive stages. Hybrids were found to
differ in their susceptibility to physical injury during process—
ing, and, also, to differ in their potential ability to germinate.

Maturity of the seed and frost injury have been reported
(18) as additional factors influencing stands in cold wet soil.
In general, cold test stands improved as the seed matured.

Arasan treated seed gave better stands than nontreated seed

in all cases. While standard laboratory germination tests indi—

cated no reduction in germination from frost, the frosted seed

gave a lower cold test germination than unfrosted seed.

MATERIALS AND METHODS

Seeds of 118 corn hybrids entered in the 1950 Michigan
Hybrid Corn Trials and seed of 120 hybrids entered in the 1951
trials were. tested for their ability to germinate under cold, wet
conditions. The seeds for the two trials were produced in 1949
and 1950, respectively. Samples, generally representative of
seed offered for sale, were submitted by the various seed com-
panies participating in the state yield trials. All seed samples
had been treated with a seed disinfectant, but the same com-
pound was not used on all of the samples.

The 1949 seed entered in the 1950 trials was tested
during the period January 21 to February 15, 1951. The 1950
seed entered in the 1951 trials was tested during the period
April 28 to May 23, 1951. In both tests, three replications
of fifty seeds each, were planted in soil in flats. The soil
was saturated with water and the flats placed in a walk—in cold
chamber maintained at 45° F for twelve days. The flats were
then moved to a warm room (70—800 F) in the greenhouse for

thirteen days. Strong seedlings were counted at this time.

5
The seedlings were cut at ground level and the average green
weight per seedling in grams was obtained.

Seeds of-four Michigan Certified hybrids (Ohio M 15,

Michigan 51 B, Michigan 11 A, and Michigan 36 B) produced
by different seed growers in 1948, 1949, and 1950 were sub—
jected to cold test germinations. The cold tests were conducted
April 19 to May 17, 1951. There were six different growers
involved and they are designated by letters. Five growers pro-
duced Ohio M 15 during the three—year period, four produced
Michigan 51 B, three produced Michigan 11 A, and two produced
Michigan 36 B. Samples of seed representative of that offered
for sale were submitted by each grower. The large flat grade

of seed was used in all cases.

EXPERIMENTAL RESULTS AND DISCUSSION

Cold test germination and average seedling green weight
for the 1949 and 1950 seed of entries made in the Michigan
Hybrid Corn Trials are presented in Table I, and the analyses
of variance in Table II. For both years, there were significant
differences among the hybrids for both characteristics.

Rag—doll germinations under standard laboratory condi—
tions were conducted on all of the seed samples. The average
germination was 98.5% and all samples were above 94%. Thus,
all of the seed was capable of a high germination percentage
under the ideal conditions of a standard germination test.

The range in cold test germination was 86.0 to 1.3%
for the 1949 seed samples and 98.7 to 19.3% for the 1950
seed samples. The averages were 46.6 and 80.0% for the
two years. The older seed (1949 cr0p) was generally lower
in cold test than the new seed (1950 (crOp).

Differences among hybrids in germination cannot be
attributed entirely to varietal differences since other factors
such as abuse of the seed in processing, maturity, and frost

injury (22, 18) may have affected the cold test performance.

TABLE 1

AVERAGE COLD TEST GERMINATION AND GREEN WEIGHT
PER SEEDLING FOR 1949 AND 1950 SEED SAMPLES
ENTERED IN THE MICHIGAN HYBRID CORN

TRIALS FOR 1950 AND 1951

 

 

 

Green Weight

 

 

Germination .
per Seedhng
Hybrids (7') (grams)
1949 1950 1949 1950
Pioneer X 5822 82.7 1.0
" 348 84. 7 1. 0
" 382 68. 7 1. 0
" 359 33. 3 0. 9
" 339 78. 0 1. 2
Pioneer X 5562 56.7 88.7 1.1 0.9
” X 7278 78.0 93.3 1.0 0.8
" 322 60.0 78.7 0.9 0.7
" 373 70.7 88.0 1.3 0.9
" 344 70.0 90.0 1.2 0.9
Pioneer 388 66. 7 83.3 0.9 0.8
" 352 72.7 90.0 1.0 0.8
" 342 76.0 86.0 1.4 0.8
" 349 86.0 88.7 1.3 0.7
" X 5643 66.0 87.3 0.9 0.9
Pioneer 377 76. 7 0. 8
” 396 90.7 1. 0
" 314 82.7 0. 6
" X 7027 96.0 1.0
" X 7036 96. 0 1. 0
" X 7164 84. 0 0. 6
" X 7164 MF 83.3 0. 7
Average 71 3 87.3

 

TABLE 1 (Continued)

 

 

 

Green Weight

 

 

Germination ,
(7‘) per Seedling
Hybrids (grams)
1949 1950 1949 1950
Funks G 30 22.0 88.0 0.8 0.9
" G 16 A 55.3 87.3 0.9 0.9
" G 6 26.7 75.3 0.9 0.7
" G 28 38.0 1.0
" G I A 48.7 1.2
Funks G 11 82.0 0.9
" G 18 86.0 0.8
" G 68 88.7 0.8
" G 188 78.0 0.9
Average 38.1 83. 6
Pfister PAG 2675 76.7 78.7 1.0 0.7
" PAG 7011 68.0 94.7 0.8 1.0
" PAG 299 69. 3 84. 0 1. 0 0. 8
" PAG 253 73. 3 88. 7 1. 1 0.8
" PAG 56 65.3 87.3 1.0 0.8
" PAG 35 76. 0 79.3 1. 1 0.9
Pfister PAG 61 74. 7 90. 0 1. 1 0.8
" PAG 2772 93.3 0.8
" PAG 4196 96.7 0.8
" PAG 4199 96.0 0.8
" PAG 4560 83.3 0.8
" PAG 7020 90.7 0.8
" PAG 7026 50.7 1.4
Average 69. 2 88. 6

 

TABLE I (Continue d)

 

 

Ge rmination

 

Green Weight
per Seedling

 

 

Hybrids (grams)
1949 1950 1949 1950
Master F 101 A 70.0 78.0 1.3 1.0
" F 82 70.0 86.0 1. 0 0.8
" F 83 52.7 78.7 1.2 0.7
" F 21 74.7 87.3 1.0 0.8
" F 60 81.3 92.0 1.2 0.8
" F 140 62.7 0.8
Average 69. 7 80.8
Haapala 120 4. 0 0. 3
” I30 6. 0 0.8
” 270 29.3 0. 6
" 300 73. 3 1. l
" 352 40.0 1. 2
" 475 17. 3 0. 9
Average 28. 3
Garno 448 A 59. 3 1. 0
" 440 52. 7 1. 3
" 451 37. 3 0. 8
Average 49. 8
De Kalb 404 A 43.3 75.3 1.1 0.7
" 406 72.7 78.7 1.3 0.7
" 240 38. 7 90.0 1. 0 0.8
" 65 32.0 78.0 0.8 0.8
" 43 56. 7 87.3 0.8 0.8

 

TABLE 1 (Continued)

10

 

 

 

Green Weight

 

 

Germination ,
(%) per Seedling
Hybrids (grams)
1949 1950 1949 1950
De Kalb 410 58.7 0.8
" 50 47.3 1.0
" 408 81.3 0.8
" 459 77.3 0.5
" 239 81.3 0.7
De Kalb 41 65.3 0.9
" 56 72.7 0.8
" 58 74.7 0.7
Average 49. 9 78. 4
Jacques 1157 J 56.7 1.0
" 1055 J 60.7 75.3 1.2 0.9
" 956 J 64.0 53.3 1.1 0.6
" 907 54.7 82.0 1.0 0.8
Jacques 1153 J 84.0 0.8
" 1107 J 86.7 0.8
" 1003 J 75.3 0.6
" G 2 81.3 0.8
" H 7 88.7 0.8
Average 59. 0 78. 3
Wolverine 55 28. 7 l. 0
" 83 18.0 80.0 1. l 0.9
" 60 40.7 62.0 0.8 0.9
" 77 75.3 90.7 1.3 0.8
" 58 53. 3 78.7 1. l 0.6

 

TABLE I (Continued)

11

 

 

Ge rmination

 

Green Weight
per Seedling

 

 

Hybrids (grams)
1949 1950 1949 1950
Wolverine 22 29.3 83.3 0.9 0.8
" 46 50. 0 74. 0 0. 9 0. 8
" 66 22.0 91.3 0.7 0.7
" 90 48.0 0.6
Average 39.7 76.0
Kingscrost KT 72.0 1.1
" KE 2 88.7 1.2
" KE 1 71.3 90.7 0.9 0.7
" KA 4 22.7 88.0 1.0 0.7
" KS 2 58.0 80.7 0.9 0.8
" KS 6 62.0 78.7 1.2 0.9
" KL 77.3 84.7 1.2 0.8
Kingscrost KO 5 91.3 0.8
" KS 3 90.0 0.8
" KS 4 86.0 0.9
" KH 3 89.3 0.7
" KY 4 92.0 0.7
" KI 82.0 0.7
Average 64. 6 86. 7
Michigan 11 A 24.0 90.0 0.9 0.9
" 24 B 49.3 83.3 0.8 0.8
" 36 B 27.3 78.0 0.9 0.8
" 51 B 43.3 84.0 1.3 0.8

 

TABLE 1 (Continued)

12

 

 

 

Green Weight

 

 

Germination ,
(7.) per Seedling
Hybrids (grams)
1949 1950 1949 1950
Michigan 20 D 72.7 95.3 1.1 0.9
" 29 D 52.0 88.7 1. 1 0.9
" 250 58.7 98.0 ' 1.0 0.9
" 350 69.3 95.3 1.2 0.8
" 480 98.7 0.8
Average 49. 6 90.1
Nosco N 4 56.0 1.5
" N 6 36.0 1.4
" N 9 46.7 1.0
" N 12 17.3 1.2
Average 39.0
Minnesota 800 42. 0 0. 9
Wisconsin 270 41. 3 1. 0
United U 17 47.3 1.3
" U 18 56.7 0.9
" U 26 39.3 0.7
" U 28 19.3 0.5
" U 32—30 77.3 0.7
" U 33 50.0 0.8
United U 20 29.3 66.0 1.0 0.8
" U 22 28.0 96.7 0.7 1.0
" U 24 20.7 90.7 0.5 0.9
" U 32 67.3 78.7 1.0 0.7
" U 32 A 68.0 62.0 1.0 0.6
Average 44. 6 67. 6

 

13

TABLE 1 (Continued)

 

 

Green Weight

 

 

 

Germination ,
(%) per Seedling
Hybrids (grams)
1949 1950 1949 1950
Supercrost F 140 25. 3 0. 9
" 85 A 1. 3 0.1
" 213 23.3 56.7 1.1 0.7
" F 112 A 8.0 67.3 0.9 0.7
” F 440 78. 0 l. 0
Average 9 14. 4 67. 3
Schumaker B 15 5.3 0.4
" B 16 37. 3 0. 8
" B 20 23. 3 0. 5
" B 28 42. 0 0. 9
Average 27. 0
Farmcraft 29 64. 7 0. 8
" 39 14.0 79.3 0.7 1.0
" 40 4.7 82.7 0.4 0.8
" 47 18. 7 0. 5
Average 12. 5 75. 6
Aldrich A 60 44. 0 1. 2
" A 61 72. 7 1.1
" 30 91.3 0. 8

Average 58. 3 91. 3

 

TABLE 1 (Continued)

14

 

 

Germination

 

Green Weight
per Seedling

 

 

Hybrids (grams)
1949 1950 1949 1950
Ohio C 54 8. 0 0. 6
" W 64 39.3 1.0
" K 62 31.3 83.3 0.9 0.9
" K 24 6.7 63.3 0.7 0.9
" M 15 31.3 92.7 0.7 1.0
" K 54 80. 7 l. 0
" K 64 69. 3 1. 0
Average 23. 3 77. 8
Iowa H 4417 48.7 0.8
" H 4560 79.3 0.9
" H 4308 72.7 0.9
" H 4567 72. 7 0. 9
Average 68. 4
Lowe 23. 3 0. 5
" 32 62. 0 1. 0
" 38 24. 7 0. 8
" 52 39. 3 1. 0
Average 37. 3
Gries 201 4.7 31.3 0.8 0.5
" 420 6.0 48.0 0. 6 0.9
" 606 4.0 54.7 0.4 0.8
Average 4 9 44. 7

 

15

TABLE 1 (Continued)

 

 

Green Weight

Germination per Seedling

We)

 

 

 

Hybrids (grams)
1949 1950 1949 1950
Indiana 419 A 19.3 66.7 0.6 0.8
" 252 A 15.3 54.7 1.0 0.7
" 210 B 62.7 0.8
" 416 B 7.3 0.4
Average 14. 0 64. 5

 

 

The correlation coefficient (Table III) for hybrids common to
both years was highly significant, 0.49, indicating that the
same hybrids tended to be high in germination in both tests.
Considering all samples from each seed company, some seed
concerns averaged higher in cold tests (Table I).

These data emphasize that large differences in stands
of corn may be expected under adverse conditions even though
all of the seed was capable of high germination under standard
laboratory conditions. State and federal seed laws require
that germination tests be conducted under ideal conditions so
that each seed is given maximum Opportunity to germinate.

Results of these tests are carried on the tags with the seed

16
TABLE II
ANALYSES OF VARIANCE FOR COLD TEST GERMINATION

AND GREEN WEIGHT PER SEEDLING FOR
1949 AND 1950 SEED

 

 

 

 

 

 

 

Degrees Mean Squares
Source of
Freedom Germination Green Weight
1949 Seed
Total 353
Replications 2
Hybrids 117 1, 676.7** 0.19**
Error 234 164.8 0.07
1950 Seed
Total 359
Replications 2
Hybrids 119 543. 8** 0. 03**
Error 238 54. 9 0. 01

 

 

** Significant at the 1% level of probability.

17

TABLE III

CORRELATION OF COLD GERMINATION
AND SEEDLING VIGOR

 

 

Degrees of

 

Freedom
Vigor 1949 - Vigor 1950 0.20 64
Germination 1949 - Vigor 1949 0.06 116
Germination 1950 — Vigor 1950 0.56** 118
Germination 1949 — Germination 1950 0.49** 64

 

 

** Significant at the 1% level of probability.

as it is offered for sale. Ideal conditions of the standard
laboratory germination test rarely prevail in the field.

In view of the large effect of stands of corn in relation
to yields (17), it appears that information on cold test per—
formance would be desirable information to include on the tag
for the seed purchaser. The buyer would know what germina—
tion to expect under adverse weather conditions following plant-
ing. This practice would stimulate the seed corn industry to
use more care in processing seed corn. Information on cold

test performance is another factor that farmers should consider

18
in choosing a hybrid for their farm. In addition to choosing
an adapted hybrid that possesses an inherent ability to germ—
inate under cold wet conditions, farmers should purchase seed
of this hybrid from concerns that are able to produce the seed
in a manner that will enable the seed to maintain this ability
after processing.

Germination and seedling vigor, as measured by average
green weight per seedling, were not related in the test of the
1949 seed (Table III), while the two characteristics were highly
significantly correlated in the test of the 1950 seed. There
was no significant relationship in seedling vigor for the two
tests.

Yield and maturity data from the 1950 Michigan Hybrid
Corn Trials (16) were used to determine if any relationship
existed with cold test germination and seedling vigor for the
1949 seed. The inconsistency of the correlations (Table IV)
indicates that, in general, there was no definite relationship
among these characteristics. Pinnel (15), also, reported no
relationship between yielding ability of double—cross hybrids

and stands in cold test trials.

TABLE IV

19

CORRELATIONS OF COLD GERMINATION AND SEEDLING
VIGOR WITH YIELD AND MATURITY

 

 

 

 

 

Germination Seedling Vigor Degrees
Counties of
Yield Maturity Yield Maturity Freedom
Monroe 0.05 0.07 0.0 0.10 48
Ingham 0. 36 —0. 01 0. 84** 0. 25 45
Kalamazoo —0. 07 —0. 10 -0. 86** -O. 30* 44
Saginaw 0. 27 0.15 0. 48** 0. 37* 38
Oakland 0. 18 0.10 , 0. 08 —0. 20 33
Newaygo 0. 40* -0. 06 0. 36* 0.17 28

 

 

* Significant at

** Significant at the 1% level of probability.

Table V presents average cold test germinations for

the 5% level of probability.

four Michigan Certified Hybrids produced by different seed

growers in 1948, 1949,

given in Table VI.

Considering each hybrid individually, there were sig—

and 1950. Analyses of variance are

nificant differences among the seed producers and there were

significant differences due to age of seed.

Seed producer F ,

TABLE V

20

AVERAGE COLD TEST GERMINATION FOR FOUR MICHIGAN
CERTIFIED HYBRIDS PRODUCED BY DIFFERENT GROWERS

 

 

Grow-

 

 

 

 

 

 

em 1948 1949 1950 Av. 1948 1949 1950 Av.
Ohio M 15 Michigan 51 B
A 48.7 59.3 80.0 62.7
B 19.3 44.0 77.3 46.9 32.0 62.7 72.7 55.8
c 46.7 46.7 64.0 52.4 28.7 29.3 57.3 38.4
D 18.0 38.0 61.0 39.1 49.3 59.3 69.3 59.3
E 42.7 66.7 89.3 66.2
F 41.3 76.7 85.3 67.8
14;:— 35.1 50.9 74.4 53.4 37.8 57. 0 71. 2 55. 3
Michigan 11 A Michigan 36 B
c 51.3 52.0 62.0 55.1
D 50.0 57.3 64.7 57.3 26.7 29.3 66.7 40.9
E 33.3 46.7 88.0 56.0
F 62.0 64.7 82.7 69.8 '
Ave“ 54.4 58.0 69.8 60.7 30.0 38.0 77.3 48.4

age

 

 

21

TABLE VI

ANALYSES OF VARIANCE FOR COLD TEST GERMINATION
OF FOUR MICHIGAN CERTIFIED HYBRIDS

 

 

Degrees Degrees

 

 

 

 

 

 

Mean Mean
Source of S uare of S uare
Freedom q Freedom q
Ohio M 15 ' Michigan 51 B
Total 44 35
Years 2 5,373.8** 2 3,358.4**
Growers 4 l, ll9.9** 3 1,368.9**
Years x Gro. 8 193. 6 6 240.6
Error 30 109. 2 24 54. 6
Michigan 11 A Michigan 36 B
Total 26 17
Years 2 576.4** 2 3,851.6**
Growers Z 562. 4** 1 l, 027. 5**
Years x Gro. 4 35. 6 2 86.2
Error 18 54. 5 12 79.8

 

 

** Significant at the 1% level of probability.

22
who is a small seed grower with a limited amount of mechan—
ical equipment, averaged significantly higher in cold test germ-
inations for' two hybrids than producers C and D, who are much
larger growers with more mechanical equipment for processing
seed. Size of Operations and amount of mechanical equipment
for processing seed are not necessarily indicative of ability to
produce seed Of highest quality. These results illustrate that
a small seed producer can produce hybrid seed corn of high
quality with a limited amount of mechanical processing equip—
ment.

Results presented in Table V indicate the differences in
germination that may occur with seed of the same hybrid pro—
duced by different growers. With new seed (1950 crop), there
were 29.3, 28.0, 20.7, and 16.9% differences in cold test for
Ohio M 15, Michigan 51 B, Michigan 11 A, and Michigan 36 B,
respectively, when produced by different growers. All seed
samples represented in Table V germinated 95% or better in
rag—doll test under standard laboratory conditions.

One and two year old seed (1949 and 1948 seed) were
significantly lower in cold test than new seed. The older the

seed the lower the cold test. One year old seed germinated

23

23.5, 14.2, 11.8, and 39.3% less than new seed for the four
hybrids, respectively (Table V). Two year old seed germinated
39.3, 33.4, 15.4, 47.3% less than new seed. Data in Table I
also show that one year old seed gave generally lower cold test
performance.

Carry—over seed corn that has a high germination in
standard germination tests under ideal laboratory conditions
has generally been assumed to be equal in quality to new seed.
The results of this study show that the germination of Old seed
under adverse conditions is likely to be lower than that of new

seed.

SUMMARY

Large differences in cold test germination were found
to exist among samples of hybrid seed corn. All samples had
a highly satisfactory germination under standard laboratory
conditions. A low of 1.3% was found in 1949 seed and a low
of 19.3% was found in 1950 seed. Hybrids that had a high cold
test performance with 1949 seed tended to be high with 1950
seed.

Associations of cold test germination and seedling vigor
were inconsistent so that it was not possible to reach a con—
clusion on the general extent of their relationship. The cor-
relations of germination and seedling vigor with yield and ma.—
turity did not indicate that there was any consistent relation—
ship among these characteristics.

Wide differences in cold test germination were present
in samples of the same hybrid produced by different seed grow-
ers. A small seed producer with limited mechanical process-
ing equipment was capable of producing seed with higher cold
test performance than larger seed growers with a more highly

mechanized proce ss .

25

Cold test germinations for one and two year old seed
were found to be lower than new seed. The older the seed
the lower the cold test germination even though all seed was
capable of very satisfactory germination under ideal laboratory
conditions.

Cold test performance was recommended as desirable

information to include on the tag.

LITERATURE CITED

Alberts, H. W. Effect of pericarp injury on moisture
absorption, fungus attack, and vitality of corn.
Jour. Amer. Soc. Agron., 19: 1021-1030, 1927.

Brown, E. B. Relative yields from broken and entire
kernels of seed corn. Jour. Amer. Soc. Agron.,
12: 196-197, 1920.

Dickson, J. G. Influence Of soil temperatures and mois—
ture on the development of the seed blight of wheat
and corn caused by Gibberella saubinetii. Jour.
Agr. Res., 23: 837-870, 1923.

 

, and J. R. Holbert. The influence of

 

temperature upon the metabolism and expression
of disease resistance in selfed lines of corn. Jour.
Amer. Soc. Agr., 18: 314-322, 1926.

Flor, H. H. Relation of environmental factors to growth
and pathogenicity of Pythium isolated from roots
of sugar cane. PhytOpath., 20: 319—328, 1930.

Hayes, H.K., I. J. Johnson, and E. C. Stakrnann. Re—
action of maize seedlings to Gibberella saubinetii.
PhytOpath., 23: 905-911, 1933.

 

Ho, Wen—Chun. Soil inhabiting fungi attacking the roots
maize. Iowa Res. Bul. 332. 1944.

HOppe, P. E., and J. E. Middleton. Pathogenicity and
occurrence in Wisconsin soils of Pythimn species
which cause seedling disease in corn. Abstract
in PhytOpath., 40: 13, 1950.

 

Johnson, Helen, James R. Holbert, and J. G. Dickson.
A Pythiurn seedling blight and root rot of dent
corn. Jour. Agr. Res., 37: 443—464. 1928.

10.

ll.

12.

13.

14.

15.

16.

17.

18.

19.

27
Koehler, B. Pathologic significance of seed coat injury
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