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Vegetable Improvement Newsletter No. 15, February 1973
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Compiled by H.M. Munger, Cornell University, Ithaca, New York

1. Effect of Seed Density on Emergence, Vigor and Production of Cucumbers

Ronald G. Eaton and J.L. Bowers

Department of Horticulture and Forestry, University of Arkansas, Fayetteville, Arkansas 72701

Two lots of seed of the cultivar Explorer, one graded as dense and the other as light and two similar lots of seed of the cultivar Bravo, were used in these studies in the spring and summer of 1972. In the field test which was seeded on June 29, the difference in rate of emergence between light seed and dense seed treatments were small and insignificant. In the greenhouse study where moisture and depth of planting were more accurately controlled, seedlings emerged faster from the dense seed lots in both cultivars than from the light grade of seed. In another test in which relatively low soil temperatures were studied (56 degrees and 63 degrees F), the rate of emergence was much faster in the dense seed lots as compared with seedling emergence from light seed.

In these studies vigor of plants as measured by length of central leader and branches was not different for two grades of seed treatment.

Yield of the cultivar Explorer was greater from the dense seed lots as compared with the light graded seed, where as the dense and light seed lots of the Bravo Cultivar were very similar in protection.

2. Selecting Cucumbers on the Basis of Green Fruit Quality

J.L. Bowers and M.J. Goode

During the period of 1969-72, the cucumber project leaders and working crew on the Southwest Branch Experiment Station, Hope, Arkansas have cut approximately 50,000 green fruit longitudinally each year. This has enabled the breeders to make selections on the basis of these internal green fruit characters: (1) freedom of carpel separation, (2) placental holliness, (3) small seed cavity, and (4) rate of seed development. It is important to keep a good sharpening stone in the field and maintain good sharp blades.

On the basis of our brining test, we have observed that considerable progress has been made in the obtainment of breeding lines which possess good internal fruit quality and it is believed that the laborious process of green fruit sectioning is responsible for the selection of these desirable pickle types.

3. Use of Hermaphroditic Cucumber Inbreds in Development of 3-Way Hybrids

L.M. Pike

Horticulture Section, Soil and Crop Science Department, Texas A&M University, College Station, Texas 77843

A new system for producing hybrid cucumbers has been proven superior to the present method, involving gynoecious by monoecious crosses. The system utilizes inbreds of three sex types; gynoecious, hermaphrodite, and monoecious.

The 3-way hybrid is derived by crossing gynoecious and hermaphroditic inbreds to obtain a 100% gynoecious F1, which is used as the female parent. The gynoecious F1 is then crossed with a monoecious inbred to obtain the 3-way hybrid.

Factors which make the 3-way cross superior to F1 hybrids using gynoecious times monoecious inbreds are summarized:

F1 female parent lines, derived by crossing gynoecious with hermaphrodite, are much more stable for the gynoecious character than inbred gynoecious lines. The stable F1 female parent eliminates the need for continual rogueing of the female parent in hybrid seed production.

Since F1 is used as the female parent in the production of 3-way hybrids, a much smaller quantity of the gynoecious inbred is needed. Therefore, a good stock of the gynoecious inbred can be easily maintained by careful rogueing. This maintenance is not easily done, when gynoecious inbreds are used as the female parent.

A reduced quantity of gibberellic acid is needed in the 3-way hybrid seed production system. This reduced expense, along with the eliminated need for rogueing, will result in a significant saving in seed production cost.

Several experimental 3-way hybrids have been tested and demonstrated to be equal or superior to present commercial F1 hybrids for quality (size, shape, color, brining, and processing characteristics) yield, and disease resistance.

4. Screening Muskmelons for Resistance to Fusarium Wilt and Powdery Mildew

David W. Davis, Carl J. Eide, and M. Shehata

Departments of Horticultural Science and Plant Pathology, University of Minnesota, St. Paul, Minnesota 55101

We have been using a seedling screening method for detecting resistance to powdery mildew and Fusarium wilt in the muskmelon breeding program; it may be of interest to other breeders. The objective has been to reduce the proportion of susceptible genotypes in segregating populations which are seeded in the greenhouse for transplanting to the field. Success has depended primarily on the timing of inoculation and on air and soil moisture and temperature. We like to transplant at a young age (about 3 1/2 weeks) and this leaves relatively little time for infection development and plant elimination prior to that time.

Vita Bands ("H") (2 1/2 " x 2 1/2") are filled to with 1/4" with a nonsterile silt loam-sand-manure (2:1:1) mix into which has been mixed a dry soil-base chlamydospore inoculum of several isolates of Fusarium oxysporum f. sp. melonis, at the rate of 4% by volume. The "manure" is a near-humus form of straw-base barnyard manure. Captan treated seed is planted in a 1/4" x 1/4" x 1/4" dibbled depression and sand is used to cover to the top of each band. The bands are held in wooden or other suitable flats on greenhouse benches heated from below. Flats are watered thoroughly after planting and are held at 70-75 degrees F. The plastic is removed at the onset of emergence. A second watering is not needed until after the plants emerge. To control damping-off the sand surface is dusted with Captan; also watering is scheduled so that the surface is dry most of the time. Fusarium wilt symptoms begin to appear at about 7-8 days after emergence.

About 5-7 days after emergence (at which time cotyledonary leaves are not quite at full expansion) powdery mildew (Race 1) spores are atomized in water suspension (or are dusted) across the flats. A clear plastic mist chamber is laid across the bench at about 1 ft. above the plant tops. Sides are pinned together to make the structure fairly tight and a Sears Moist Air Vaporizer is used to maintain relative humidity at about 90%. Temperature is kept 75 to 85 degrees F. by adjusting the clipped edges of the plastic sheets used to make the chamber.

Susceptibles, having powdery mildew lesions on cotyledonary leaves, are removed. After about 8-10 days flats are taken from the chamber and are placed for 4-5 days in a cold frame for acclimatization prior to transplanting in the field. Symptoms of mildew may or may not continue to appear in the cold frame depending on ambient air temperature. Continued onset of wilt symptoms under these conditions seems more likely to occur.

Because we are on a time schedule and like to transplant when plants are young, there are temporary escapes from both diseases. However, we feel that we can eliminate 60-80% of the susceptible plants prior to removal to the field and, because they are incubating the diseases, the remaining susceptible plants show symptoms in the field fairly soon. Many of these populations also are segregating for the dwarf or short internode plant form; we space plants close together in the row and eliminate normal vine types and additional susceptible plants early in the season; elimination by the time of female flowering is nearly complete.

The use of nonsterile soil and a fairly low concentration of inoculum do not provide a clear, quick kill of plants with moderate degrees of resistance to Fusarium; resistant plants are not likely to be killed. Although our resistance source is quite strong, we hope that we are also retaining minor genes for resistance and that over time this will result in an increase in horizontal or non-specific resistance.

5. Resistance to Rabbit Feeding in Muskmelon

Warren S. Barham

Basic Vegetable Products, Inc., P.O. Box 599, Vacaville, California 95688

A muskmelon variety which has been grown near Santa Rosa, California for about 75 years, and generally referred to as Crane Melon, was given me. This muskmelon produces large, sparsely netted, thick, good quality, green flesh fruit. It was crossed with Gulfstream, a shipping type cantaloupe developed by Fred Andrus of U.S.D.A. Vegetable Breeding Laboratory at Charleston, South Carolina. The F1 of Crane x Gulfstream (C. x G.) was very vigorous and prolific; the fruit were large, fairly well netted and had good to excellent flavored, very thick, orange color flesh.

In a planting grown near Dixon, California in 1970, rabbits seriously damaged all plants of Gulfstream, all other shipping type cantaloupes, and some F2 plants of C. x G. All of the plants of Crane, F1 of C. x G. and some of the F2 plants of C. x G. were undamaged. No evidence could be found of feeding on plants that were classed as undamaged; whereas, damaged plants had most of the foliage and tender stems eaten. There were not enough F2 plants for inheritance studies; however, it was concluded that resistance is controlled by one or more dominant genes. No further data on the inheritance to rabbit feeding has been collected by me. Seed of the F2 generation have been supplied to two cantaloupe breeders and a few seed are available if others are interested.

6. Monoecious Muskmelons with Round Fruit

H.M. Munger

Department of Plant Breeding, Cornell University, Ithaca, N.Y. 14850

For many years we have been transferring the monoecious gene from Banana into Iroquois with the idea of using it as a female parent for hybrid seed production. Eleven backcrosses have been made - 4 to Plant Breeding 13, a round fusarium resistant line, followed by 7 to Iroquois. In spite of selection for the most nearly round fruits, the monoecious segregates have consistently been identifiable by their longer fruit shape and slightly pointed ends. Andromonoecious segregates have been indistinguishable from Iroquois during the last few backcrosses. The monoecious segregates have also had larger fruit size, difficult slip, less netting, and slightly inferior flesh color and flavor.

Wall's report of C. melo var. dudaim as a round-fruited monoecious melon (Euphytica 16:199-208) led us to start again with this different source of the gene. In the first four backcrosses the association of monoecious flowering with longer fruit showed up as it did with the Banana source of monoecious. At this point, I realized that all crosses had been made with monoecious plants as female in order to save the trouble of emasculating and that there might be a cytoplasmic influence.

Therefore the fifth backcross was made in 1971 with Iroquois as the female as well as the usual way. Although reciprocals did not appear different when grown side-by-side in the field in 1972, the cross with Iroquois as female had already been grown in the greenhouse and an additional backcross made, the 6th. Both the fifth and the sixth backcrosses in the greenhouse gave monoecious plants with fruits more nearly like Iroquois than we had ever seen before, typical netting, good slip, and nearly round shape.

The F2 of the sixth backcross was grown in the field in 1973 and most of the monoecious plants gave fruit remarkably similar to Iroquois and to the andromonoecious segregates in shape, netting and size. The color and depth of flesh were not as good as in Iroquois and further backcrosses are being grown to improve these characteristics.

As a result of expressions of interest from visitors who saw the round monoecious type, seed in small amounts will be made available as a germplasm release to melon breeders.

7. Sources of Variation in Evaluating Quality of Squash Varieties

H.M. Munger

Cornell University, Ithaca, NY

As a laboratory exercise in a plant breeding course, we have used organoleptic evaluation of winter squash, Cucurbita maxima, to demonstrate the use of a doubly balanced incomplete Block design as described by Calvin (Biometrics 10:61-88. 1954). At the same time we get information about some of our breeding material. The results suggest that subjective evaluation of quality is not so variable and unreliable as we originally assumed.

The experiments in 1971 and 1972 both included samples of 8 varieties, each a composite from about 5 baked fruits. The design called for 14 blocks with 4 samples in each, and therefore had 7 replications. Each entry occurred 3 times in the same block with every other entry. Each person tested one block of 4 samples, rating each one on a scale from 1 (Very poor) to 5 (Very good). The tasters included people who like and who dislike squash, people familiar and unfamiliar with it, and nearly half were from outside the U.S.

The incomplete block design is used to avoid taster fatigue which can introduce variability if each taster tries to rate all the samples. The adjustment of means provided by the design permits the removal of variability caused by different tasters having different sets of varieties. Nevertheless, the adjusted means differed only slightly from the unadjusted means obtained simply by averaging the seven ratings given each entry (Table 1). Therefore the experiments in 1971 and 1972 failed to demonstrate as much value for the incomplete block design as anticipated.

The results do show considerable variation between the two years for a given entry. Either the varieties responded differently to growing conditions in the 2 years or five fruits did not constitute an adequate sample. In squash at least, it appears than we need to be much more concerned about the representativeness of the samples presented to tasters than about the variability of ratings given by tasters.

Table 1. Adjusted and unadjusted mean quality ratings for squash varieties tasted in a balanced incomplete block design- 1971 and 1972.

Quality rating means (5=best)
1971
1972
Variety
Seed Lot
Adj.
Unadj.
Adj.
Unadj.
Delicious inbred 509
68-13
2.3
2.3
4.1
4.1
Delicious inbred 509 m.s.
68-201-4x204
3.6
3.4
Delicious inbred 515
68-14
2.4
2.4
Delicious inbred 515 m.s.
68-211x210
1.0

1.1

Hybrid A (509x515)
1960 and 1971 seed
3.1
3.0
3.4
3.1
Hybrid A-ms (509x515)
69-73x74
3.4
3.3
Hybrid A-ms (509x515)
69-75x74
4.2
4.1
3.9
4.0
Queensland Blue
2.4
2.6
4.1
4.0
Gold Nugget
2.9
2.9
2.1
2.1
Butternut 23 - Asgrow
*
2.0
2.0
Waltham Butternut - R.E. Young
*
2.7
2.9

*46 students making a paired comparison in 1971 expressed a slight but distinct preference for Butternut 23.

8. Breeding for Stalk Lodging Resistance in Sweet Corn

Stuart N. Smith

808 E. Lincolnway, Rte. #2, Ames, Iowa 50010

Minnesota A632 is a dent corn inbred with very good resistance to stalk lodging. This resistance is being transferred successfully to sweet corn ear parents, using the same system employed in developing the massive root system of Nebraska N28 in sugary lines.

Stalk lodging in sweet corn is important to everyone who makes use of the product even though it is a primary problem only to seed producers. The reason is because stalk lodging frequently reduces seed vitality and this influences cost both to the consumer and the producer.

Field corn breeders have done commendable work in reducing stalk lodging where corn is produced for grain. This work was begun by breeders of open pollinated corn back in the 19th century with major further improvement made by hybrid seed breeders. Sweet corn has not had the benefit of an equal amount of research. This stems in part from the fact that very little of it is harvested for use as grain and the problem occurs mostly after the crop is mature. The major cause of this type of lodging is stalk rot, mostly from various forms of fusarium and diplodia. When stalks on seed parents break over, the ears are subject to cob rot, premature germination and incipient kernel rots which reduce seed vitality.

Good dent corn inbreds offer the best source for improving stalk lodging in hybrid sweet corn ear parents. Some of these have extra thick and woody stalk walls and we have found them apt to carry tough pericarp over into sugary lines. Others like A632 have a quick transition period from the green stage where they are highly resistant to stalk rot, to the dry stage where rot cannot continue due to lack of moisture. The technique being used is the same as was followed with good results in transferring the heavy root system of Nebraska N28 over to sugary lines acceptable in quality. It consists of one or two generations of selfing between backcrosses to the recurrent sugary line. Heavy nitrogen applications are used to insure favorable conditions for stalk lodging. Selection is rigid for resistance, regardless of quality, until sugary lines equal to A632 are obtained. Quality is then sought for in later backcrosses.

9. Uncatalogued Vegetable Varieties Available for Trial in 1972

This list is aimed at facilitating the exchange of information about potential new varieties, or new varieties which have not yet appeared in catalogues. Persons conducting vegetable variety trials who wish seed of items on this list should request samples from the sources indicated.

It is the responsibility of the person sending out seed to specify that it is for trial only, or any other restriction he may want to place on its use.

Crops are listed alphabetically. For each entry the following information is given: Designation, source of trial samples, outstanding characteristics, variety suggested for comparison (not given separately if mentioned in description), status of variety (preliminary trial, advanced trial, to be released, or released) and contributor of information if different from source of trial samples. Where several samples are listed consecutively from one source, the address is given only for the first.

10. Stocks Desired