mVALUATlCN OF Fl HYBAID IIChLING CUUUhdndb

By

Jack Le Roy heigle

AN ABSTdACT

Submitted to the School for Advanced Graduate Studies of
hichigan State University of Agriculture and
Applied Science in partial fulfillxent of

the requirements for the degree of

DUUTOd OF PHILOSOPHY

Department of horticulture

1956

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Abstract

The value of hybrid pickling cucumbers for use in commercial
production was investigated. To accomplish this purpose observations
were recorded on four experiments conducted during 1955 and 1956. Two
of these were composed of single hill plots in a latin souare design,
planted with flour variety and their six possible hybrids. In these
trial plants in the 6-7 leaf stage were inoculated with cucumber mosaic
virus 1. The other two experiments had Large plots in a randomized
block design with three replications. Observations were recorded for
yield, mosaic fruit symptoms as a mosaic index, fruit shape, length-
width ratios, salt stock quality and pressure tests of the fruit, both
fresh and from salt stock.

Some hybrids were at least enual to the best variety in yield and
mosaic index, although none was statistically better in all trials. The
results of the observations made on the types of unsatisfactory fruit
shape did not allow any conclusion to be formed concerning the relationship
between hybrids and standard varieties, because results for the two years
were not consistant. This lack of correlation between years may indicate
that hybrids have greater ability to produce in years of abnormal growing
conditions.

Observations on length-width ratios indicate that the hybrids have
ratios intermediate between the parents in most cases. This presents the
possibility of utilizing in hybrids superior inbreds which do not have
acceptable length-width ratios. A hybrid can be produced with a specified
length-width ratio in one year by testing a number of such combinations.

whereas, if an attempt is made to produce a variety with a certain length-

width ratio in combination with the other desired characteristics, it
would probably take many years.

The results obtained from quality evaluations of salt stock and
pressure tests on the fruit were not conclusive and indicate the need
for further experiments with processed material.

The true value of hybrids becomes apparent only if these data are
considered as a group. Although none of the hybrids was statistically
superior to the standard varieties in any one characteristic, in 1956
the hybrid Shi 18-7 x MR 25 rated best when all criteria for evaluation
were considered. This combination of good qualities was not found in

any of the standard varieties.

EVALUATION OF Fl hYBdID PIChLING CUCULBEJS

By

Jack Le Roy heigle

A TnLSIS

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

DOCTOi OF PhlLOSOPnY

Department of Horticulture

1956

I £141.. .5 f

‘F'.

Acknowledgement

The author wishes to acknowledge the guidance and constructive
criticism given by Dr. C. E. Petersen during the course of this
investigation. Appreciation is also expressed for the help and
encouragement given by Dr. R. L. Carolus, Dr. G. B. hilson, Dr. 5. E.
Down, and Dr. D. J. deZeeuw, members of the guidance committee. Further
acknowledgement is given to Dr. D. J. deZeeuw for providing the virus
inoculum and assisting in its application. The suggestions of Dr. S. K.

Ries on statistical methods also were appreciated.

Table of Contents

I. Introduction .................................................. I
II. Review of Literature .......................................... 2
A. History of neterosis ...................................... 2

B. Some Hybrids Used in Commercial Production ................ h

C. Heterosis in the Cucumber ................................. 8

III. haterials and hethods ......................................... 12
A. Field Trials .......;...................................... 12

B. Determination of hosaic mesistance ........................ 13

C. Shape and Quality of the Fruit ............................ 15

D. Statistical methods ....................................... 20

IV. ixperimental iesults .......................................... 21
V. Discussion .................................................... 36
VI. Sumnary and Conclusions ....................................... 42

VII. Literature Cited OOOOOOOOIOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOO 1"“

I. Introduction

The application of heterosis to a crop of commercial value was first
realized with the production of hybrid seed corn. Although heterosis in
corn was observed by deal (I) in 1880 and greatly publicized by Shull (36)
and East (10) in 1909, seed corn was not produced on a commercial scale
until l93U. by 19AO ninety per cent of the corn acreage in the United
States was planted with hybrid seed. The commercial success of hybrid
corn provided the necessary incentive for plant breeders to investigate
the possibilities of using hybrids of other crops. At present, hybrid
seed is produced commercially in the following vegetable crops: sweet
corn, onions, tomatoes, squash, eggplant, and slicing cucumbers (Hayes, 16).

Since hybrid seed is always more expensive to produce, its advantages
must be important enough to more than outweigh the added production expense.
Otherwise, a hybrid could not gain commercial acceptance. The slicing
cucumber hybrid has passed this test and is widely accepted in commercial
production.

Hybrid vigor, measured by yield alone, is generally not as striking
in cucurbits.as in some of the other crops. Therefore, if hybrids are to
be of value in cucumber and related creps, attributes other than yield
increases should be investigated.

This study was undertaken to determine the possible advantages in
using Fl hybrid pickling cucumbers. The evaluation is concerned with

quality factors and disease resistance, as well as early and total yield.

II. Review of Literature
A. History of heterosis

Since various authors have employed the term heterosis to cover
different concepts in the past, it would appear advisable to define the
term. According to Shull (37), who introduced the term, "heterosis is the

reater vigor or capacity for growth frequently displayed by crossbred
animals or plants as compared with those resulting from inbreeding”. He
also stated that heterosis and hybrid vigor are synonymous. These
definitions will be used in this dissertation with the additional stipula-
tion that to be commercially important a hybrid must also exceed the
standard variety in yield and/or quality.

Lany excellent reviews of literature on the subject of heterosis are
in existance. In the symposium "heterosis" (12) the first three papers
written by Zirkle, Shull, and Hayes are particularly applicable. In
addition, East and hayes (11) give an excellent review of the early
literature and Hayes, Immer and Smith (I?) of the more recent material.
Since the literature on heterosis is very extensive and has already
received excellent treatment in the above publications, this review of
the general subject will be confined principally to the most important
papers since 1900.

In a thorough study of cross and self fertilization, Darwin (7)
found self fertilization to be detrimental and cross fertilization to be
beneficial in many instances. However, since the method of transmission
of characteristics from parent to offspring were not understood at that
time, he was unable to explain his findings on a genetic basis.

The work of Mendel (31), which showed that plant characteristics
were inherited in a definite manner, was rediscovered in 1900. with this
knowledge Shull (36) and East (10) were able to conclude that inbreeding
was a process of obtaining homozygous lines and not just a process of

degeneration as believed by Darwin (7). Since Shull and East knew what

happened during inbreeding, they were able to propose a valid theory
concerning the reason for the increase in vigor of the hybrid progeny
over that of the parents. According to this theory the highest degree
of hybrid vigor is obtained by crossing two lines which are heterozygous
at the highest number of loci. Their conclusions were based mainly on
data from field corn experiments such as the one reported by Shull (36)
in which the average height of the parent inbreds was 19.28 dm. while
that of the F1 was 25.00 dm. The average yield in bushels per acre
was 29.04 for the inbreds and 63.07 for the F1. Open—pollinated corn
derived from the same original material averaged 22.9h dm. in height and
yielded 61.52 bushels per acre. According to the theory proposed by
Shull and East the hybrid is not only more heterozygous than its inbred
parents but also more heterozygous than the Open-pollinated material.

D. F. Jones (21) proposed a different theory to explain hybrid vigor.
He contended that the increased vigor found in hybrids was the result of
an accumulation of additive growth factors inherited from both parents.
his explanation of the reason that open-pollinated corn is not as vigorous
as hybrid corn is that deleterious genes are linked with many of these
growth factors. These deleterious genes accumulate in open-pollinated
corn but many of them may be eliminated through inbreeding. Thus the
inbred parents contain the growth factors without as many of the
deleterious genes as found in the open-pollinated varieties of corn.

Subsequent experiments by Jones (23) revealed instances in which
crosses between inbred lines, differing by only a single gene, resulted
in a significant yield increase. This would mean that heterozygosity at
one locus could cause hybrid vigor as hypothesized by Shull (36) and East
(10) .

In contrast to the expression of heterosis caused by allelic interaction,

 

as described above, Powers (34) concluded that heterosis in tomatoes may
be caused by interaction of non—alleles. When a tomato inbred which
produced a few large fruit was crossed with an inbred producing many small
fruit, the average number of fruits produced by the hybrid was below the
mean of the two inbred parents. Likewise, the average size of fruit was
smaller than the mean of the two inbred parents. In total yield of ripe
fruit, however, the hybrid exceeded the highest yielding parent. Thus it
would appear that the non—allelic yield factor concerned interact in a
manner which is multiplicative in respect to total yield.

In their review of the experiments dealing with heterosis, Bayes,
Immer, and Smith (17) state that "heterosis, like other size characters,
results from the combined action and interaction of allelic and nonallelic
factors." It appears that in the opinion of these authors no single
theory offers a complete explanation of the phenomenon of heterosis.
Instead they have used a combination of the theories of Shull (36), East
(10), Jones (21), and Powers (BA) for their explanation. Since these
theories have proven to be sound in specific instances, it would seem
proper that a general statement as to the factors responsible for heterosis

should include all four.

B. Some hybrids used in commercial production

When hybrid corn was first discovered, it was thought to be of no
practical value to the farmer, because controlled pollination and low seed
yield made the hybrid seed too expensive. The added expense of producing
hybrid seed must be lower than the increase in profit from its use. however,
D. F. Jones (22), by using the double cross method, was able to increase
the seed yield without materially reducing the amount of hybrid vigor.

This proved to be the beginning of the hybrid seed era. The greater part

of the corn acreage in the United States is now planted with hybrid seed.
Hybrid vigor also has proven to be of commercial value in many other crops,
particularly in the vegetable industry.

In hybrid sweet corn the results obtained and production methods
involved are similar to those of field corn with one exception. It is
possible to use the single cross hybrid for commercial seed because the
inbreds used as female parents produce a proportionally greater amount of
seed than those in field corn. In addition to the increased yield, hybrid
sweet corn has the advantage of producing more uniform ears than the Open-
pollinated varieties. This improves its appearance, and therefore its
value, when sold on the fresh market. The uniformity of hybrid sweet corn
also makes possible mechanical harvesting and handling which are so
important in the processing industry. This characteristic also would be
beneficial in other crops in which more than one harvest is required
because of uneven maturation of the plants.

However, corn is the only crop in which pollination can be controlled
by such a simple procedure as detasseling. Although the sexes are also in
separate inflorescencesin most cucurbits, the number of male inflorescences
is much greater than in corn and flowering continues over a more prolonged
period. In other species, such as the onion, the male and female flower
parts are found in the same flower. These facts make hand emasculation,
as practiced in corn, too expensive for commercial seed production in the
majority of other crops. Thus, it is necessary to find methods of reducing
or even eliminating costly hand emasculation before hybrid seed of most
vegetable crops could be economically produced.

The discovery of a male sterile onion plant in the Italian med variety
by Jones and Emsweller (26) solved the problem of hand emasculation in this

crop. Male sterility in the onion was found by Jones and Clarke (24) to

result from the interaction of genetic and cytoplasmic factors. They also
described the method by which these factors could be introduced into a
desirable inbred for use as the female parent in hybrid seed production.

As in other crOps, increased yield is not the only advantage gained
through use of hybrid onions. Jones and Davis (25) noted that keeping
quality, reduction in bolting, and uniformity in size and shape were other
desirable qualities which had been secured. However, these qualities are
not the result of hybrid vigor as such, but instead depend on the selection
of the proper inbreds to be used in the hybrid combination. Inbreeding of
onions results in a reduction of vigor and yield so that, although the
inbreds are of high quality, their commercial production would not be
economical. Therefore, a hybrid which can combine yielding ability equal
to or better than the standard variety with other qualities superior to
the standard would be of commercial importance.

An example of this would be the hybrid bonanza (27) which yielded
692 50-pound bags at Parma, Idaho, compared to 528 for the standard,
Brigham Yellow Globe. This difference was significant at the one percent
level. In addition, the ratings made after storage for firmness, scale
retention, absence of root growth, and color were higher in every case for
bonanza. Similar results were obtained in two different years and at
another location.

In the self-pollinated crops, such as tomato, where inbreeding does
not reduce yield, yet a different benefit of heterosis becomes apparent.
Many hybrids will begin bearing earlier than either parent. This is
important for the fresh market because the first few pickings often are
worth more than all those which come later and in the case of indeterminate

tomatoes which generally bear until frost, the longer the bearing season,

the higher the total yield will be. Wellington (43) found not only
increased early yield, but also an increase in midseason and late yield

in some hybrids. This could result from the fact that this hybrid reached
its peak maturity earlier. Burgess (2) found the hybrid lritchard x med
River hA-9 to be superior in early yield to the standard varieties usually
grown in Maine. However, a statistical analysis was not performed in
either of the above experiments.

In eggplant, a close relative of the tomato, 0dland and Noll (33)
found that the yields of some hybrids were significantly better than that
of their parents which were standard commercial varieties. The hybrids
had greater early and total yield, as well as a more uniform fruit shape,
but fruit size of the hybrid fruit was near the mean of the parents.

Unlike some crops that can be either self or cross-pollinated in
nature, the squash, Cucurbita maxima and Q; pepo, generally do not lose
vigor upon inbreeding. In this respect they behave like the normally
self-pollinated crops. Haber (14) was able to maintain the yield, size
of fruit, and quality factors of a Q; pgpg at or above the level of the
commercial varieties during ten generations of inbreeding. Cummings and
Jenkins (5) obtained the same results with an inbred strain of lemgximg.

In reference to hybrid vigor in squash, Bushnell (3) reported very
little increased yield from hybrids as compared to the parent inbreds
derived from lemggimg. However, these inbreds were closely related so
little hybrid vigor should have been expected. Hutchins and Croston (20),
working with Qg'mggimg inbreds of more diverse origin, found that hybrids
outyielded the higher yielding parent by a statistically significant
difference in seven out of ten crosses. Curtis (6) observed hybrid vigor
in a Q&.pgpg hybrid although his data were confined to early yield. Curtis

also outlined a method of hybrid seed production for bush type squash which

set only a small number of blossoms. He suggested that if the rows used
as females were hand-emasculated three times and the fruit set during this
period were marked, a good supply of hybrid seed could be harvested from
the marked fruit. The amount of extra labor involved should add little

to the cost of the seed.

C. Heterosis in the Cucumber

The first report of heterosis in the cucumber was by Hayes and Jones
(18). When the variety White Spine was crossed with Fordhook Famous and
London Long Green, the average increase of the hybrids over the higher
parent in number of fruit per plant was 6.h in the first cross and 8.0 in
the second. These hybrids also showed an increase in average weight of
fruit per plant of h.3 and 2.7 pounds respectively. Average weight of
individual hybrid fruits was intermediate between that of the parents in
each case. In this example, hybrid vigor was manifested chiefly in the
number of fruits per plant. when Fordhook Famous was crossed with London
Long Green no hybrid vigor was secured. The authors concluded that this
failure to exhibit hybrid vigor might have been due to genetic similarity
since the two parents were similar in appearance.

Hutchins (19) obtained similar results by crossing an early-bearing
pickling variety with several late-bearing slicing types. In addition,
the hybrids produced early yields which were much larger than the average
of the parent varieties.

Lindsey (30) made crosses between inbred lines of slicing types instead
of using commercial varieties as parents. One of his crosses out-yielded
its parents by 50 percent, but no comparison was made with a standard
variety. The hybrids also were of higher quality than their parents as

measured by percent of No. l fruits.

A pickling cucumber hybrid developed by Graham (13) did not out-
yield certain other varieties under ideal climatic conditions, but it did
surpass these same varieties when the weather was cold and wet or when the
plants were subjected to periods of drought during the growing season. A
similar instance of increased resistance to adverse environmental conditions
was observed in certain tomato hybrids by Nalkof and Huttall (A2). Thus,
another advantage of some hybrids is the ability to stand adverse growing
conditions. It is possible that whereever this characteristic appears it
may cause the average yield for the hybrid to be higher over a period of
years even though it may be lower in individual years when growing
conditions are favorable.

In the field of disease resistance, Doolittle (8) found that the
hybrid, Tokyo Long Green x Vickery Forcing showed considerable resistance

to bacterial wilt (g; tracheiphilus HHS). A direct comparison between

 

the hybrid and its parents was not included in the data, but the hybrid
was more resistant than the standard varieties.

Shifriss, et al (35) tested several hybrids for resistance to
cucumber mosaic virus I by inoculating plants in the cotyledon stage.
Hybrids of symptomless x susceptible lines shoWed slight symptoms but
recovered quickly and maintained luxuriant growth. Hybrids of tolerant
x susceptible were somewhat stunted in early stages, but eventually they
overcame this condition while susceptible parents were severely stunted
under the same conditions. The statement was made that from a practical
standpoint this resistance is dominant.

One of the most important considerations to the practicability of
commercial utilization of hybrid cucumbers is method of seed production.

The available information concerning the production of slicing cucumber

10

hybrids by the seed companies indicates that hand pollination is employed
exclusively. Other less expensive methods are being sought for the
production of hybrid pickling cucumber seed.

One of these methods is based on the reduction of the staminate-
pistilate ratio by maleic hydrazide as described by hittwer and Hillyer
(AA). 'Wittwer and Peterson (45) conducted a trial crossing block using
this method. The rows to be used as females were sprayed with 750 ppm. of
maleic hydrazide at the first true leaf stage and again at the A to 5 leaf
stage. The male rows were untreated. The normal staminate to pistilate
ratio in the summer season would be between 10:1 and 30:1. The varieties
differed considerably in their response to the maleic hydrazide treatment
as is shown by the following staminate to pistilate ratios determined
from data collected between August 6 and August 25, 195A: ShR l2, 2.3/1;
em 9, 0.6/1; Dark Green National, 2.1/1; hodel, 1.3/1; ha 25, 0.9/1;

SR 6, 1.4/1. During this period the staminate flowers were removed before
anthesis and the fruit which had set between these dates were marked

for identification at harvest. The mechanics of this method are similar
to those used by Curtis (6) to produce hybrid seed of Cucurbita pepo.

Another possidle method for the production of hybrid cucumber seed,
similar to that being used by Jones, et a1 (28) for producing hybrid
spinach seed, is being studied now at hichigan State University. This
method depends on the use of the gynomonmnious character found in the
Korean variety Shogoin. In this variety, approximately fifty percent of
plants are gynmcious and the remainder are monmxious instead of all the
plants being mournious as in the standard varieties being grown in this
country. An attempt is being made to introduce this character into

inbreds which might be used as the female parents in hybrid seed

11

production. If such a parent line should be developed it would be
necessary to remove all the monaxious plants from the rows planted to

this female parent, as well as, any fruit already set on the gynoecious
plants at the time of rogueing. because of the unpredictable flowering
habit of cucumbers it is considered advisable to check the supposedly
gynmnious plants as often as possible and remove any that bear staminate
flowers. If too many staminate fIOwers are found on the plants of the
female parent then all the fruits must again be removed from the gynoecious
plants because of the possibility of sib—pollinations. It may be possible,
according to present information, to develop gynomonanious lines that
contain 50 percent or more gynanious plants. If this goal is attained
then the extra labor involved in the production of hybrid cucumber seed

would be nominal.

12

III. haterials and hethods
A. Field Trials

During the 1955 growing season four cucumber varieties and the six
possible hybrids between them were grown in a 10 x 10 latin square as
outlined by Cochran and Cox (A). The varieties included in this trial
were SR 6, SHR 12, ER 25, and HH 17. SR 6 is a scab resistance, mosaic
susceptible variety which yields well early in the season. Its fruit
shape is considered satisfactory by most processers when the fruit do not
show severe symptoms of mosaic. ShR 12 is resistant to both scab and
mosaic. It also yields well early in the season. Its fruit shape is
satisfactory in a moderate climate, but the fruit tend to have a severe
blossom end taper under hot dry conditions. RH 25 is a scab susceptible,
mosaic resistant variety with a very poor early yield. However, its
fruit have better shape under a wide range of climatic conditions than
most other varieties. hR 17 is also scab susceptible and mosaic resistant.
Its fruit shape is not as good as that of MR 25, but it is a better
yielder early in the season.

Each plot in this design consisted of a single hill containing three
plants. The plants were started in the greenhouse in four inch pots,
each hill in a pot, to provide more uniform conditions for germination
and early growth. The plants were transplanted to the field when the
first leaf was one-half expanded. Five plants were placed in each hill
and later thinned to three.

A similar procedure was followed during the 1956 growing season, but
two of the varieties were different. The experimental varieties HSU 1
and SHR 18-7, both of which have scab and mosaic resistance, were planted
in place of MR 17 and Shi 12, causing five of the six hybrids to differ

also.

 

I'll-Ill.l|l

13

The plots were picked twice a week during 1955 between July 23 and
August 31. The number of fruits and the weight of the fruits in grams
was recorded for each plot. The cool, wet weather in 1956 made it
impractical to pick twice a week, so no set schedule was followed.
Instead the cucumbers were picked between July 23 and September 11
whenever they reached satisfactory size. The weight of the fruit was
recorded to the nearest one—tenth of a pound in 1956.

Certain of the varieties and hybrids studied in the single hill
plot experiments described above were also included in larger yield
trials connected with evaluation of varieties. In 1955, the varieties,
MR 17 and SHR 12, along with their hybrid, were included in this type
of yield trial. The plots, two rows wide and fifty feet long, were
replicated three times. Weight of fruit was recorded in pounds per
plot and converted to bushels per acre.

A similar*large plot test was conducted in 1956. This trial included
the varieties Ski 12, MR 17, MR 25, hSU l and Shd 18—7 and the hybrids
between he 25 and each of the other varieties. height of fruit was

recorded for both early and total yield.

B. Determination of hosaic Resistance
When the plants were in the 6 to 7 leaf stage, the terminal leaves
were inoculated with cucumber mosaic virus I. hxpressed sap from infected

cucumber and Nicotiana glutinosa plants in approximately 1:1 dilution

 

with distilled water was used as the inoculum. This material, with a
small amount of 00 carborundun added, was applied to the growing points
by an atomizer under a pressure of 20 psi.

The variety Sd 6, which was included in both trials, was very

susceptible to cucumber mosaic virus I. All the other varieties used

 

{I 1" I'll it)

14

were tolerant to this disease to the degree that the plants showed very
few symptoms when inoculated in the 6-7 leaf stage. However, the fruit
of all varieties showed some symptoms. Fruit symptoms, instead of plant
symptoms, are the most important to the pickling industry, and, according
to Sinclair and halker (38), they are the most reliable criteria for
judging resistance. Hunger and Newhall (32) found little correlation
between the appearance of the plant and fruit symptoms. Therefore, it
was decided to make observations for mosaic resistant on the basis of
fruit symptoms.

The fruit were divided into four classes according to the severity
of symptom expression. These classes were none, slight, moderate, and
severe. The class with no symptoms is self-explanatory. Slight included
those fruit which had a faint mottle in the dark-colored section on the
stem end of the fruit. In the moderate class were those fruit which had
a distinct mottle showing well defined areas of alternating light and
dark green. Severely affected fruit were of two types: Distorted fruit
with dark green raised areas and fruit that were uniformly a very light,
glossy green color. The latter type is commonly known in the processing
industry as "white pickle".

As a means of comparison, mosaic ratings were computed for the
various varieties and hybrid for each of the three pickings on which
observations were made. To compute a rating these classes were assigned
values as follows: none-0, slight-l, moderate-2, and severe-3. The
number of cucumbers in each class was then multiplied by the assigned
value and the resulting products for each variety were totaled. This
total was divided by three times the number of fruit in all classes for

the variety being considered. The results of this division, multiplied

15

by 100, was used as the mosaic rating. An example follows.

Class No. of fruits Assigned value Products
None LO 0 0
Slight 25 1 25
hoderate 10 2 20
Severe _5_ 3 .31.
Totals 80 , 60

hosaic Rating = jig-8'0 x 100 - 25

The ratings range from 0 to 100. A variety with a mosaic rating of
0 would bear fruit which would be free of any symptoms of the disease.
If the rating were 100, all the fruit would be severely affected. The
intermediate ratings indicate increasing severity of infection as the
numbers become larger. The calculated ratings for three pickings each

year were analyzed statistically.

C. Shape and Quality of the Fruit

One method of indicating the general shape of a cucumber is the
lengthdwidth ratio. Such measurements were made in this experiment with
the use of an instrument which gives the length-width ratio directly.
The principle by which.this is accomplished is shown in Figure 1. The
ratios were determined on cucumbers which were 7/8 to 1 1/8 inches in
diameter. Difficulty in making such measurements was encountered during
the latter part of the picking season because the fruit shape was not
always typical, particularly in varieties and hybrids which were in some
degree susceptible to cucumber mosaic virus I.

For a more precise comparison of shape the individual fruit of each

variety or hybrid were pflaced in one of four classes: normal, tapered

 

 

 

 

 

 

 

 

 

 

 

16

\“\\\\\
W

 

 

 

 

 

9.0

/ ’ ‘ '- - _-

/
l
I
k

\ /

\ /

\
\
\
Figure I. Instrument for measurement of length-width ratios of the fruit

of pickling cucumbers with sample in place.

l7

stem end, tapered blossom end, and curved. During the 1955 season
difficulty was encountered in placing some of the fruit in any of these
four classes because of a type of deformity characterized by a
constriction in the center of the fruit. In the 1956 season a fifth
class was added to include these constricted fruits. Outlines of the
longitudinal sections of these five classes are illustrated in Figure II.

Each of the above classes was subdivided into two groups, slight
and severe, according to the amount of deformity. Those in the severe
group was misshapen to such an extent as to be unacceptable for processing
as whole pickles and would be called culls by the processers. The slight
group included cucumbers which, although deformed to a small degree,
would still be acceptable for processing as pickles. The latter group,
therefore, would be the same as normal pickles from a commercial
standpoint. However, such information should be of value to a plant
breeder for the purpose of establishing varietal trends as far as shape
is concerned.

The results of flliS classification were tabulated to present the
percentages of fruit which were judged to show slight or severe expression
of the four types of defects for each of three pickings. No attempt was
made to analyze statistically these data in this form. Instead, the
percentages of culls, including all types of defective fruits, were
analyzed.

In order to compare the salt stock quality of a hybrid with its
parents, samples of the hybrid RR 17 x Ska l2 and its parents from the
1955 large plot trial were bagged and placed in brine tanks at a salting
station. When curing was completed, an evaluation of the fruit was

conducted by a panel of commercial processers on the basis of the following

g‘

 

 

18

 

 

 

 

 

Severe Constriction Slight Constriction Normal
Severe Curve Slight Curve

Figure II. Longitudinal sections of pickling cucumber fruit in the

various shape classes. (Figure continued on the next page).

19

 

 

 

 

 

 

Severe Stem
End Taper Slight Stem

End Taper

 

 

Severe Blossom Slight Blossom
End Taper and Taper

Figure II ( continued ). Longitudinal sections of pickling cucumber

fruit in the various shape classes.

20

factors: color, shape, firmness and general acceptability. Since Jones
and Etchells (29) found that pressure readings were a good indication of
firmness in salt stock, such a test was conducted on these fruit with a
modified Magness-Taylor pressure tester with a 5/16 inch head (Heller, 15).
Jones and Etchells also indicated that the relationships between pressure
readings of varieties in salt stock should be similar to those of the
fresh fruit. Therefore, in 1956, pressure readings were determined on

the fresh fruit of the varieties and hybrids in both the single hill

plot trial and the large plot trial.

D. Statistical Methods

Significant differences between means were determined by the New
Multiple flange Test as proposed by Duncan (9). For the application of
this method the means were ranked in decending order. Each pair of means
has a different least significant range; the size of which depends on
the position of the two means in the ranked order. If the two means are
one after another in rank, then the least significant range will be at
its smallest. However, if the two means are at the extremes of the ranked
order, then the least significant range will be at its largest. This
variation in the size of the least significant range allows an accurate
test of significance to be determined for any pair of means within a
particular experiment.

The percentages of culls were transformed to angles before the
analyses of variance were calculated from these data. The methods used

have been outlined by Snedecor (AO).

21

IV. Experimental Results

The analyses of variance of the number and weight of fruits, both
early and total yield, for 1955 are recorded in Table I. It should be
noted that the varieties and hybrids differ at the one percent level of
significance in all four analyses. The mean yields from these data,
shown in Table II, indicate that SR 6 is significantly lower than the other
entries in all four methods of estimating yields. The other varieties
MR 25, MR 17, and SMR 12, are significantly different from one another
in yields based upon weight of fruit (Table II, C and D). These varieties
ranked from low to high as listed above. This same order appears in
Table II, A and B, where mean yields are based upon the number of fruit,
although not all of the differences are significant. In overall yielding
ability the hyarids having SR 6 as one parent are among the lower entries
(Table II). This is particularly true of the hybrid m 17 x SR 6. The
yield of the hybrid kR l7 x.MR 25 is intermediate, while SLR 12 x ER 17
and SHE 12.x MR 25 along with the variety ShR 12 are in the highest
yielding group. Thus, the latter three hybrids yielded approximately
equal to their higher yielding parent. The hybrid MR 25 x SR 6 not only
produced as many fruit as its higher yielding parent NR 25, but also a
greater weight of fruit than this same parent. The other two hybrids
were intermediate between their parents.

Highly significant differences among the yields of the varieties
and hybrids grown in 1956 are indicated in the analyses of variance in
Table III. The comparisons of means from this data are found in Table
IV. Again, SR 6 is the lowest yielder in all four methods of measurement,
but it is not significantly lower in early yield than the varieties,

ha 25 and MSU 1 (Table IV, A and C). Although hSU l is also low in total

22

Table I. Analyses of variance of numbers and weights of pickling cucumber

fruits obtained from the 1955 mosaic-inoculated, single hill plot trial.

 

A. Number of fruits from.the first 6 pickings

 

 

 

 

 

 

 

Source df Sums of Squares Mean Squares F Values
Total 99 13573

Varieties 9 7929 881 16.62**
Replications 9 1001 111 2.09*
Columns 9 8A9 9b 1.77
Error 72 379k 53

B. Total number of fruits

Source df Sums of Squares Mean Squares F Values
Total 99 781lh
Varieties 9 51036 5670 23.82**
Heplications 9 5716 635 2.67*
Columns 9 3983 AAB 1.86
Error 72 17397 238

C. Weight of fruits from the first 6 pickings

Source df Sums of Squares Mean Squares F Values
Total 99 1007738
Varieties 9 574919 63880 18.13**
Replications 9 119328 13259 3.76**
Columns 9 59800 6644 1.89
Error 72 253691 3523

D. Total weight of fruits

Source df Sums of Squares Mean Squares F Values
Total 99 2252637
Varieties 9 1526085 169565 26.77**
Replications 9 153000 17000 2.68**
Columns 9 117550 13061 2.06*
Error 72 #56002 6363

 

* Significant difference at the 5% level
** Significant difference at the 1% level

Table II. Mean number and weight of pickling cucumber fruit from the
varieties and hybrids in the mosaic inoculated, single hill plot yield

trial during 1955.

 

 

 

 

 

 

A. Number of fruit, first 6 pickings B. Total number of fruit
Variety or hybrid Mean Variety or hybrid Mean
SR 6 23 a* SR 6 AZ a
MR 17.x SR 6 33 b ha 17.x SR 6 66 b
MR 25 38 be SR 6 x.SMR 12 86 c
MR 25 x SR 6 38 bc mm 25 87 c
MR 17 x.MR 25 38 be MR 25 x 83 6 90 c
SR 6.x SMR 12 #1 c MR 17 x.hR 25 91 c
MR 17 AB d RR 17 93 c
SMR 12 xKMR 17 #9 d SLR 12 x MR 17 113 d
SMR 12 x.MR 25 #9 d Ska 12 x.LR 25 117 d
SMR 12 55 d SkR.12 120 d

C. Weight of fruit, first 6 pickings D. Total weight of fruit
Variety or hybrid Mean ** Variety or hybrid Mean
SR 6 138 a SR 6 199 3
MR 25 209 b RR 17 x SR 6 338 b
MR 17 x.SR 6 226 be ME 25 378 b
MR 17 x MR 25 266 cd SR 6.x SMR 12 45h c
MR 25 x SR 6 293 de MR 25 x SR 6 #77 c
SR 6 x.SMR 12 296 de hR 17 A80 c
MR 17 309 de MR 17 x MR 25 488 c
SMR 12 x MR 25 3&5 ef SMR 12 595 d
SMR 12 x.MR 17 387 f ShR 12 x.MR 25 601 d
SMR 12 391. f Shh 12 3: Mi 17 612 d

*Means not followed by the same letter are significantly different from
each other at the 5% level. For example, MR 17 differs from SR 6 and
MR 17 in number of fruit in Section A.

**Mean weight of fruit is recorded to the nearest 10 grams.

2h

Table III. Analyses of variance of numbers and weights of pickling

cucumber fruits from the 1956 mosaic-inoculated, single hill plot trial.

 

A. Number of fruits from the first 5 pickings

 

 

 

 

 

 

 

 

Source df Sums of Squares Mean Squares F Values
Total 99 5280
Varieties 9 1571 175 5.30“
Replications 9 977 109 3.30**
Columns 9 321 36 1.09
Error 72 2411 33
,B. Total number of fruits

Source df Sums of Squares Mean Squares F Values
Total 99 28571
Varieties 9 10111 1123 7.25**
Replications 9 4118 458 2.95**
Columns 9 3205 356 2.30*
Error 72 11137 155

C. Weight of fruits from the first 5 pickings

Source df Sums of Squares Mean Squares F Values
Varieties 9 66.65 7.41 4.09**
Replications 9 9.52 1.05 .58
Columns 9 3.53 .39 .22
Error 72 130.28 1.81

D. Total weight of fruits

Source df Sums of Squares Mean Squares F Values
Total 99 800.11
Varieties 9 317.03 35.23 8.55**
Replications 9 146.42 16.26 3.95**
"Columns 9 40.38 4.49 1.09
Error 72 296.28 4.12

 

* Significant difference at the 5% level
** Significant difference at the 1% level

25

Table IV. Mean number and weight of pickling cucumber fruit harvested from

the varieties and hybrids in the mosaic inoculated, single hill plot yield

trial during 1956.

 

A. Number of fruit, first 5 pickings

B. Total number of fruit

 

Variety or hybrid Mean Variety or hybrid Mean
SR 6 16 a* SR 6 32 a
MR 25 20 ab MSU l 47 b
MSU 1 20 ab MSU 1 x.SR 6 48 b
MSU 1 x SR 6 23 be Shh 18-7 x SR 6 50 b
SMR 18-7 x SR 6 24 be MSU l x SMR 18-7 53 be
MSU 1 x SMR 18-7 24 be MR 25 54 be
SMR 18-7 25 be SMR 18-7 58 bed
SR 6 3: MR 25 25 be SR 6 3: MR 25 59 bed
MSU 1 1 MR 25 27 cd MSU l 3: MR 25 64 cd
SMR 18-7 XLMR 25 31 d SMR 18-7.x MR 25 70 d

 

C. Weight of fruit, first 5 pickings

 

variety or hybrid Mean **
SR 6 1.9 a
MR 25 2.3 ab
MSU 1 2.4 ab
MSU 1 x SR 6 3.1 abc
SMR 18-7 x.SR 6 3.1 abc
SI‘iR 18.7 302 be

SR 6 1: MR 25 3.4 bc

M30 1 x SMR 18-7 3.5 bc
MSU 1 x.MR 25 3.8 cd
SMR 18-7 x.MR 25 6.9 d

 

Variety or hybrid

. D. Total weight of fruit

Mean

 

SR 6
hSU 1
MSU 1 x.SR 6
SMR 18-7 x SR 6
SMR 18-7

MSU 1 x SMR 18-7
MR 25

SR 6 x.MR 25
MSU 1 szR 25
8MB. 13-? 2: MR 25

000 0000
OU"O‘C7‘O"CJ"b

0.9.0000
0.9.

OOQQ-QfiO‘O‘UIUD
WNNQrFWONO‘N‘I

H

0

“Q0
0

 

* Means not followed by the same letter are significantly different from
each other at the 5% level.

** Mean weight of fruit is recorded to the nearest one-tenth of a pound.

26

yield, MR 25 has a relatively better ranking (Table IV, A and C). The
hybrid SMR 18—7 x MR 25 produced the highest yield based upon both number
and weight of fruit in early and total pickings. In doing so it yielded
significantly better than either parent in all methods of measurement
except total number of fruit. The other two hybrids containing RR 25 as
one parent did nearly as well.

As shown by the analyses of variance in Table V, the mosaic indices
differ with high Significance in the years, 1955 and 1956. Section C
and D of Table V indicate that SR 6 has a mosaic index which is significant-
ly higher than the other entries in both years. In 1955 the mosaic
indices of hybrids containing Sn 6 as one parent were higher than all the
other entries except SR 6. However, this is not true in 1956 as shown in
Table V, D. Here the hybrid SR 6 x.MR 25 is grouped statistically with
the resistant entries which include its other parent MR 25. This resistant
group also include its other parent MR 25. This resistant group also
includes the other two hybrids having MR 25 as one parent. Overall, the
mosaic indices were considerably lower in 1956 than in 1955, indicating
that the disease was much less severe in 1956.

Table VI expresses the percentages of fruit from the 1955 harvest
which fell into the various shape classes. These data point to a certain
pattern of shape among the varieties tested. The main defect in the shape
of MR 25 appeared to be stem end taper, while MR 17 had a tendency to
curve or taper on the blossom end. The variety SMR 12 was particularly
susceptible to severe blossom end taper. SR 6 was not included in these
tabulations because the majority of its fruit were distorted by mosaic
virus. The data in Table VI indicate that hybrids have the shape defects

of both parents. The percentages of total culls are also recorded in this

27

Table V. Analyses of variance and mean of the mosaic indices of pickling

cucumber fruit from mosaic inoculated trials in 1955 and 1956.

 

A. Analysis of variance, 1955

 

 

 

 

 

 

Source df Sums of Squares Mean Squares F Values
Total 29 8811
Varieties 9 8180 909 36.36**
Replications 2 174 87 3.48
Error 18 457 25

B. Analysis of variance, 1956

Source df Sums of Squares Mean Squares F Values
Total 29 4920
Varieties 9 4504 500 26.32**
Replications 2 73 37 1.95
Error 18 343 19

C. Mosaic indices, 1955 D. Mosaic indices, 1956

Variety or hybrid Mean Variety or hybrid Mean
MR 17 X.MR 25 7 a* SMR 18-7 x,MR 25 l a
MR 25 9 a mu 1 x MR 25 3 ab
MR 17 10 ab MR 25 4 ab
SMR 12 12 ab SR 6 x.MR 25 5 ab
SMR 12 15 abc MSU 1 x SMR 18-7 7 abc
SMR 12 x MR 25 18 bcd SMR 18-7 7 abc
MR 25 x SR 6 23 cde MSU l 10 be
SR 6 x SMR 12 25 de SMR 18-7 x SR 6 11 be
MR 17 x.SR 6 30 e MSU 1 x SR 6 15 c
SR 6 66 f SR 6 46 d

 

* Means not followed by the same letter are significantly different from
each.other at the 5% level.

** Significant difference at the 1% level.

 

1.1-4

28

Table VI. Shape classifications, expressed as percentages, of pickling
cucumber fruit harvested from the varieties and hybrids in the mosaic

inoculated, single hill plot trials during 1955.

 

 

Variety Curved fruit Stem end taper Blossom end Normal Total
or taper of
Hybrid Slight Severe Slight Severe Slight Severe Culls*
MR 25 19 5 22 9 13 3 29 17
MR 17 23 7 ll 0 31 10 18 17
Ska 12 14 2 12 6 29 29 8 37
MR 25 x SR 6 23 4 23 10 15 9 16 22
MR 17 xTMR 25 20 4 18 2 24 11 21 18
MR 17 x SR 6 14 3 23 9 18 18 15 30
SM‘R 12 x MR 17 11 4 14 5 19 30 l7 33
SMR 12 x MR 25 10 4 21 13 22 15 15 31
SR 6 x SMR 12 14 4 16 14 23 14 15 32

 

* Percentage of fruit having a severe defect of any type as computed from
the original data.

29

table. In spite of the fact that they range from 17 to 38, the differences
among the percentage were not significant because of the extreme variability
of the samples.

The data for 1956 (Table VII) indicate that the major defect of all
the varieties and hybrids tested was blossom end taper. In addition, the
variety MR 25 had a tendency for constricted centers and curved fruit,
while the added defect for MSU 1 was constricted centers and for SMR 18-7
it was curved fruit. The data for 1956 summarized in Table VII indicate
that hybrids have a combination of the defects of both parents as they
did in 1955, although the percentage of any one defect is not as great
as that of the highest parent. Another result similar to that obtained in
the previous year is the lack of significant differences among the
percentages of total culls.

The varieties planted in 1955 show some variation in length-width
ratios as illustrated in Table VIII, A. The variety MR 17, with a length-
width ratio of 3.0, was relatively long and slender compared to MR 25 and
SMR 12, both of which had a ratio of 2.6. SR 6 was omitted because the
mosaic effect would cause such measurements to be out of proportion. when
the variety MR 17 was crossed with either of the blockier varieties, MR 25
or SMR 12, the resultant hybrids had intermediate length—width ratios.
When two varieties with the same ratio, such as SMR 12 and MR 25, were
crossed, the ratio for the hybrid was identical to that of the parents.
Similar fruit shape relationships are shown in Table VIII,_B for the 1956
season.

In part C of Table VIII the 1956 pressure readings are recorded. The
pressure reading for the hybrid MSU 1 x, SR 6 is shown as intermediate

between its parents, while the reading for SMR 18-7 x SR 6 is indicated

30

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31

Table VIII.Lengthdwidth ratios and pressure readings of pickling cucumber

fruit harvested from the varieties and hybrids in the mosaic inoculated,

single hill plot trials during 1955 and 1956.

 

A. Length-width ratios, 1955

Variety or hybrid

Mean

 

SR 6.x SMR 12
MR 17.x SR 6
MR 25

SEE 12

SMR 12 szR 25
MR 25 x.SR 6
SMR 12 3: MR 17
MR 17 x.MR 25
MR 17

WNNNyNNNN
OCD‘QK'IO‘O‘O‘VXUI

 

C. Pressure readings in psi., 1956

B. Length-width ratios, 1956

 

Variety or hybrid Mean
Md 25 2.5
MSU 1 x.MR 25 2.6
SMR 18-7 x.MR 25 2.6
SMR 18-7 x_SR 6 2.6
MSU 1.x SMR 18-7 2.6

 

 

Variety or hybrid Mean
SMR 18-7 x SR 6 16.0
MSU 1 16.5
SMR 18-7 x MR 25 17.0
MSU 1.x SMR 18-7 17.0
MSU 1 x.SR 6 18.0
SR 6 19.0
MR 25 19.0

 

32

as well below either parent. In contrast to this, the hybrid RSU l x
MR 25 had a pressure reading above both parents. Therefore, no constant
pattern in the relationship between hybrids and parents can be found
in these data.

The two varieties, MR 17 and SLR 12, and their hybrid were included
in a large plot yield planted in 1955. Their yields were not significantly
different, but some interesting data were obtained about quality factors

and pressure readings on samples from salt stock as shown in Table IX.

Table IX. Quality Evaluation of Pickling Cucumbers from Salt Stock.

 

 

 

Variety or . Quality Factors* Pressure
Hybrid Color Shape Firmness Acceptability Readings
MR 17 12 10 13 10 15.8
MR 17 x SMR 12 15 15 15 16 lh.2
ShR 12 1h 13 15 13 13.8

 

m--.'-n---

* The four quality factors were rated by a panel of four processers giving
a value of 1-4 for each. The best possible score for each factor is 16.
The hybrid appears to be superior to both parents in quality, and in
this instance the pressure reading was between the parents.

The rankings of mean yields obtained in the 1956 large plot tests
(Table n, A and B) show similar order to those obtained with the single
hill plots (Tables II and IV). The hybrids, SmR 18-7 x RR 25 and SAR 12 x
LR 25, yielded the best in this trial, as they did in the smaller trials.
Likewise the yield of the variety Sufi 12 was not significantly different
from that of its hybrid Shi 12 x MR 25 in both types of trials. However,
Table IV, D shows the relative rankings of MR 25 and MSU l x MR 25 as

much higher than those calculated from the large plot results.

33

‘Table X. Analyses of variance of weights, length-width ratios, and

pressure readings of fruits of pickling cucumbers from the 1956 large

plot trial.

 

A. Height of fruits, first 6 pickings

 

 

 

 

 

 

 

Source df Sums of Squares hean Squares F Values
'Varieties 11 3186.08 289.6h 5.53**
'Replications 2 1235.04 617.52 11.79%*
Error 22 1152.20 52.37
B. Total weight of fruits

Source df Sums of Squares Mean Squares F Values
Total 35 12320.12
Varieties 11 8512.h3 773.86 10.31**
Replications 2 2157.10 107.86 1.h4
Error 22 1650.59 75.03
C. Length-width ratios of fruits

Source df Sums of Squares Mean Squares F Values
Total 39 .63
Varieties 9 .60 .044 7.33**
Replications 3 .07 .023 3.83*
Error 27 .16 .006
D. Pressure readings of fruits

Source df Sums of Squares Mean Squares F Values
Varieties 9 h6.l8 5.13 6.04**
Replications 5 5h.70 1.09 1.28
Error 35 29.8h .85

 

* Significant difference at the 5%V1evel
** Significant difference at the 1% level

 

'A

3h

Table XI. Yield, length-width ratios, and pressure readings of pickling

cucumber fruit harvested from the 1956 large plot trial.

 

A. Yield in bu./A., first 6 pickings

B. TOtal in bUO/Ao

 

 

 

 

 

Variety or hybrid Mean Variety or hybrid Mean
MR 25 68 a* MR 25 198 a
MSU l 82 b MSU l 201 a
MR 17 8h bc MR 17 218 b
MSU 1 x.MR 25 95 c MR 17 x.MR 25 235 c
SMR 18-7 109 d MSU l x.MR 25 2h0 c
hR 17 x.MR 25 111 de SMR 18-7 269 d
SLR 18-7 1 MR 25 116 def SIuR 12 280 de
SMR 12 1: MR 25 122 of $.18 12 1 MR 25 281. e
SMR 12 125 f SMR 18-7 x‘MR 25 291 e
C. Length-width Ratios D. Pressure readings in psi.

Variety or hybrid Mean Variety or hybrid Mean
SMR 12 2.5 a SMR 12 13.5 a
PR 25 2.6 ab MSU l ll..5 ab
hSU 1 x.MR 25 2.6 ab Shh 12 x‘hR 25 1A.5 ab
SMR 12 1: MR 25 2.6 ab MR. 17 15.0 bc
8M3 18-7 2.7 bc Sufi 18—7 15.0 bc
raw 1 2.7 bc I-ZSU l 3: MR 25 15.5 bc
MR 17 x.MR 25 2.7 bc MR 25 16.0 c
SMR 18-7 1: MR 25 2.7 bc MR 17 3: MR 25 16.0 c
MR 17 2.8 c SMR 18-7 x;hfl 25 16.0 c

 

* Means not followed by the same letter are significantly different from
each other at the 5% level.

35

Because of the lack of significant differences among the majority
of the length-width ratios recorded in Table II, C, it is not possible to
make any direct observations. Nevertheless, these data indicate a similar
relationship between hybrid and parents as found in Table VIII, A and B.

The same type of situation also exists among the mean pressure
readings (Table XI, D). Although the extreme values are statistically
different, the intermediate values are not. however, a tendency is
observed in these data for the pressure reading of the hybrid either to

fall between the two parents or to be equal to the higher parent.

V. Discussion

When evaluating a newly introduced variety, growers generally show
the greatest interest in its yield as compared to standard varieties.
Therefore, the first consideration as to the desirability of hybrid pickl-
ing cucumbers should be a comparison of the yields of hybrids with those
of standard varieties. Hutchins (l9) and Hayes and Jones (18) have
reported that hybrids gave greater yields than standard varieties, but
these results were obtained with the slicing instead of the pickling
type of cucumber.

In this thesis data are presented from four yield trials conducted
during 1955 and 1956, which included pickling cucumber hybrids. Only in
the 1956 small plot trial did a hybrid have a significantly higher yield
than the best variety. This hybrid was SMR 18-7 x ER 25 and the highest
yielding variety in the trial was hi 25. Unfortunately, this trial did
not include Shd 12 which had outyielded MK 25 in other experiments. kore-
over, when this hybrid was grown with Shh 12 during the same season in the
large plot trial, the yields of the two were not significantly different.
Thus, a statement that a hybrid had yielded higher than the standard
varieties could not be substantiated by these data.

This does not mean that hybrid vigor as expressed by increased yield
can not be found in pickling cucumber hybrids. Quite possibly the parents
used in these experiments were not as diverse in genetic origin as those
used to make the slicing cucumber hybrids which have shown yield heterosis.
The pickling varieties now grown in hichigan are all closely related
because the same sources of resistance to the scan and mosaic diseases
were used in their breeding. In addition, the variety National Pickling

was generally used as the pickle type parent.

If inbreds are developed from material of wider genetic origin, it
should be possible to find a hybrid combination that would outyield the
best variety under hichigan conditions. The variety hi 25 should be a
source of good inbreds as it exhioited excellent general combining ability
in all trials. Such an inbred may be one parent of a future successful
pickling cucumber hybrid.

Disease resistance could be considered a part of yielding ability
because a variety without the proper resistance will be unable to produce
a satisfactory yield. The Variety, National Pickling, formerly was the
favorite in hichigan, but since it is susceptible to both scab and mosaic
disease, it is no longer used by hichigan growers. The newer variety
SR 6 yields very well in regions where the mosaic disease is not prevalent.
However, data from the two mosaic inoculation trials presented here show
what happens to Si 6 when it is attacked by the mosaic virus. Not only
did the yield decrease, but most of the fruit produced were not acceptable
for processing.

According to hunger and Newhall (32), the inheritance of mosaic
resistance is controlled by many genes. This makes it difficult to combine
in one variety a high level of mosaic resistance with the many genes for
yield and quality. It would be much easier to fix as many of these factors
as possible in each of two inbreds and then cross them to make a hybrid
which should contain a larger number of the desired genes than could be
retained in a variety produced by selection. It is also possible that
hybrid vigor in itself might provide an increase in disease resistance
in addition to that controlled directly by the resistance genes.

Although they were not significantly different from the standard

varieties, hybrids did have the lowest mosaic indices as calculated from

38

inoculated trials. However, it should be noted that the varieties with
the low mosaic indices appear to have been bred primarily for mosaic
resistance with a resultant deficiency in either quality or yield. The
superiority of a hybrid becomes apparent when all three factors yield,
mosaic resistance and quality are considered. An example is the cross,
SHE 18-7 x hR 25 which, in 1956, was higher in yield but lower in
percentage of culls and mosaic index than the standard varieties. One of
the most important factors concerned with quality of cucumbers in their
fresh state is the percentage of culls. In order to accomplish a more
thorough study of culls, the fruits were divided into groups according
to the type of deformity. In 1955 the hybrids showed no advantage over
the best-shaped varieties. In fact the trend was in the opposite direction.
however, in 1956 this trend was reversed. One explanation of this occurrance
may be found in the work of Graham (13). In his trials one hybrid produced
better quality fruit than the standard varieties, but mainly in years of
abnormal climatic conditions. The unusually cool, wet, season of 1956
provided abnormal conditions for that trial at East Lansing in which
hybrids made their best showing.

The relationship between cucumber fruit shape and environment was
investigated by Tiedjens (41). he found that anything interfering with
the development of the embryo influences the shape of the fruit because
uneven distribution of the seed necessarily produces an irregularly
shaped fruit. Some of the factors found to be responsible for misshapen
fruit were interruption of growth, lowered carbohydrate supply and late
pollination. Any of these could be caused by the environmental conditions
associated with a cool, wet season like that experienced during 1956 in

.EaSt I-IanSing e

39

It appears possible that the lower percentage of culls produced by
hybrids in years with unusual climatic conditions may be the result of the
ability of the hybrid to adapt to an unusual environment. However, since
the climate is satisfactory for growth of the standard varieties in most
years, this characteristic of some hybrids would be of small advantage
unless the hybrid could also at least equal the yielding ability of the
standard varieties during normal years.

Environment is not the only factor involved in control of fruit
shape. It would be impossible to obtain fruit of good shape from a
hybrid, if its parents had genes for poor fruit shape, regardless of the
environment to which it was subjected. It appears that the fruit shape
in the cucumber is controlled by many genes as found in the related crop,
Cucurbita pepo by Sinnott (39). Thus, the difficulty of breeding pickling
cucumber varieties which produce a minimum number of culls would be the
same as that involved in breeding for mosaic resistance. The particular
hybrids tested in this study emphasize the need for developing parent
inbreds which produce better shaped fruit.

The length-width ratio is a measurement of overall shape. It is of
value to the processor for indicating the general shape of the pickle he
wishes to pack so that he may have a uniform product from year to year.
In addition, the glassware for fancy packs is designed to accomodate a
certain size and shape of pickle. Therefore, if the length-width ratio
of the pickles were to be changed considerably, it would detract from the
appearance of the packaged product.

Thus, length-width ratios are of concern to the breeder if he is to
produce a variety acceptable to the processing industry. However, if

superior lines are found whose ratios deviate greatly from the accepted

AO

norm, they need not be discarded completely. As indicated from the data
presented in this thesis, a cross between two varieties having quite
different length-width ratios generally will produce fruit which have a
ratio intermediate between the two parents. Therefore, a breeding program
for development of hybrids could utilize exceptionally good lines which
might otherwise be discarded because their length-width ratios make them
unacceptable as varieties. By crossing a line having long, narrow fruit
with one that Produce short, wide fruit, a hybrid cucumber with a satis-
factory length-width ratio should be produced.

Even though a cucumber has the desired shape and length-width ratio
it will not be acceptable to the pickling industry unless it processes
satisfactorily and remains attractive until sold to the consumer. To
evaluate any variety or hybrid for processing quality it is necessary to
actually process the cucumber in brine and Observe the resultant salt
stock. Only one hybrid was subjected to such a test and, as shown in
Table IX, it was rated superior to its parents by a panel of four
processors. However, one such test is not sufficient evidence on which
to base an opinion. The results of this trial indicate the need for
additional work on quality evaluation of processed hybrids and parent
lines.

Firmness of the fruit also can be estimated by a fruit pressure
tester according to Jones and Etchells (29). They found that the relative
differences between varieties indicated by pressure testing were very
similar to those obtained by manual testing. However, an exception to
this similarity of results of the two methods can be found in the data
shown in Table IX. In this trial the variety bk 1? had the highest

pressure reading of all the entries but was given the lowest firmness

_. e_“; f

rating by the panel. Possibly ha 17 has a tough peel, which would cause
the pressure reading to be high, and a soft interior, which would result
in a low firmness rating when tested manually. If this is true, it would
indicate a need for a revision in the method of pressure testing in order
to increase its correlation with actual firmness of the pickle. Perhaps,
if a small section of the peel were removed as is done in pressure testing
the apple, the results of the pressure tests on cucumber salt stock would
be more accurate.

The relationship of hybrids and parents with regard to pressure test
value is not clear. It appears that the inheritance of the factors in the
fruit which are responsible for this value are controlled by many genes.
Additional experiments Should be planned to investigate this relationship
more thoroughly.

Although hybrids were not statistically superior to standard varieties
when the different criteria for evaluation were considered singly, they
appeared to have merit if the results of all the criteria were combined.
An example has been given of a hybrid which was the best in the three most
important tests: yield, mosaic index and acceptable shape. Since these
results were obtained by crossing the available, rather heterozygous
commercial varieties, it should be possible to produce superior hybrids
through a long term breeding program which would include the development

of superior inbred lines to be used in production of F1 hybrids.

42

VI. Summary and Conclusions

The value of hybrid pickling cucumbers for use in commercial
production was investigated. To accomplish this purpose observations
were recorded on four experiments conducted during 1955 and 1956. Two
of these were composed of single hill plots in a latin square design,
planted with four variety and their six possible hybrids. In these
trials plants in the 6-7 leaf stage were inoculated with cucumber mosaic
virus 1. The other two experiments had large plots in a randomized block
design with three replications. Observations were recorded for yield,
mosaic fruit symptoms as a mosaic index, fruit shape, lengthewidth ratios,
salt stock quality and pressure tests of the fruit, both fresh and from
salt stOCK.

Some hybrids were at least equal to the best variety in yield and
mosaic index, although none was statistically better in all trials. The
results of the observations made on the types of unsatisfactory fruit
shape did not allow any conclusion to be formed concerning the relationship
between hybrids and standard varieties, because results for the two years
were not consistant. This lack of correlation between years may indicate
that hybrids have greater ability to produce in years of abnormal growing
conditions.

Observations on length—width ratios indicate that the hybrids have
ratios intermediate between the parents in most cases. This presents the
possibility of utilizing in hybrids superior inbreds which do not have
acceptable length-width ratios. A hybrid can be produced with a specified
length-width ratio in one year by testing a number of such combinations.

Whereas, if an attempt is made to produce a variety with a certain length-

A3

width ratio in combination with the other desired characteristics, it
would probably take many years.

The results obtained from quality evaluations of salt stock and
pressure tests on the fruit were not conclusive and indicate the need
for further experiments with processed material.

The true value of hybrids becomes apparent only if these data are
considered as a group. Although none of the hybrids was statistically
superior to the standard varieties in any one characteristic, in 1956
the hybrid Shd l8-7 x ER 25 rated best when all criteria for evaluation
were considered. This combination of good qualities was not found in

any of the standard varieties.

1.

2.

9.

10.

12.

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