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Vegetable Improvement Newsletter No. 23, February 1981
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Compiled by H.M. Munger, Cornell University, Ithaca, New York

1. Anthocyaninless Asparagus

Lincoln G. Peirce

Department of Plant Science, University of New Hampshire, Durham, N.H. 03824

Asparagus varieties currently available in the seed trade show substantial purple coloring at the spear base and, to varying degrees, at the spear top. As a product of a rather long development project, a line has been selected at New Hampshire in which spears lack such coloration, appearing instead as bright green from base to tip. Those who have tasted this line have commented on its sweetness, and it seems to have less "after-effect" than most commercial varieties.

The inheritance of the anthocyaninless trait has been somewhat perplexing in that it has been assumed, based upon observation throughout the development process, to be recessive. However, it is possible to cross two green parents and produce approximately 15% purple-stemmed segregates, suggesting possible complementary inheritance or interaction with an inhibitor gene. Crosses have been made to attempt to elucidate the genetic basis for 'anthocyaninless' in this line.

In the meantime, several green lines which yield only green progenies have been intercrossed to produce seed and crowns (designated UNH G-81). Some of these have been consigned to cooperators for test. Very limited numbers of crowns or seed, however, can be made available this spring to scientists interested in testing for adaptation or disease resistance.

2. Cucurbita maxima from Argentina

Thomas W. Whitaker

Collaborator, SEA, AR, USDA, P.O. Box 150, La Jolla, CA 92038

The purpose of this note is to alert squash breeders to new material of Cucurbita maxima Duch., that has recently become available through the Plant Resources Germplasm Laboratory, BARC-West, Beltsville, MD 20705. Limited amounts of seed may be obtained from Dr. D.D. Dolan, USDA/PI, Seed & Vegetable Sciences Dept., N.Y.S. Agricultural Experiment Station, Geneva, N.Y. 14456.

My wife and I spent the month of October, 1980, in Argentina collecting Cucurbita, and incidentally a few ornamentals. Except for the northern provinces adjacent to the Bolivian border such as Salta, Jujuy, and Chaco, we covered most of the likely areas where Cucurbita might be found. Because planting had not yet commenced (it was early spring) we did not see plants in the field. Thus our collections were confined to seeds obtained from fruits secured in the markets, seeds from lines developed by experiment station personnel, and seeds obtained from herbarium specimens. We arranged for additional collections when the fruits mature.

We made about 75 collections of Cucurbita maxima and about a dozen collections of C. andreana Naud., a feral species. Cucurbita andreana is a close relative of C. maxima, and is thought by some investigators to be the wild progenitor of the cultivated C. maxima. The fruits of C. andreana contain bitter substances, cucurbitacins. The substances have recently assumed great theoretical and practical importance in studies of the coevolution and control of the Diobrotocite beetles (Metcalf, et al, 1980; Rhodes, et al, 1980).

We feel that squash breeders should test this material for disease resistance and quality factors. It is possible that adequate testing will reveal useful genes of great value in squash improvement programs.

Varieties of C. maxima currently in use in this country stem mostly from a very narrow base. Material from these new collections has the possibility of diversifying this base with resulting benefits to growers and consumers.

Literature Cited

  1. Metcalf, R.L., R.A. Metcalf and A.M. Rhodes. 1980. Cucurbatacins as kairomones for Diabroticite beetles. Proc. Natl. Acad. Sci. (USA) 77(7): 3769-3772.
  2. Rhodes, A.M., R.L. Metcalf and E.R. Metcalf. 1980. Diabroticite beetle responses to cucurbitacins kairomones in Cucurbita hybrids. J. Amer. Soc. Hort. Sci. 105(6): 832-842.

3.A Suggested Procedure for Maintaining Homozygosity in Gynoecious Cucumber Parent Lines

H.M. Munger and Hsiao Chi-Hsiung

Departments of Plant Breeding and Vegetable Crops, Cornell University, Ithaca, NY 14853

Some seedsmen have mentioned to us their problem of maintaining complete homozygosity of the gynoecious character in parental cucumber lines. We have seen evidence of this problem in lack of complete hybridity in certain hybrid cucumber samples. We have also been told that Cornell gynoecious lines are more stable than others. We can accept this as being true for Tablegreen, but not for our other gynoecious releases. Marketmore 70F produces many more males than either Tablegreen 68 or Gy57, if the latter is truly homozygous gynoecious. SR551F produces practically as many males as either Gy3 or Gy14 when treated in a comparable manner. We have found occasional heterozygous gynoecious plants in the original seed received from Dr. Barnes for both Gy57 and Gy14 and have not looked for them in Gy3. We conclude that the impression of greater stability in the Cornell gynoecious lines comes from their being either completely homozygous or more nearly homozygous for this character than some other releases. This prompts us to outline the procedure we have used with the hope that it may be useful to others.

Our procedure is based on self pollinating plants that we think are homozygous gynoecious by reason of their producing a small number of male flowers when treated with a male-inducing chemical. We then check on the homozygosity of those plants by growing each selfed progeny separately under conditions which cause heterozygous gynoecious plants (Ff) to produce many more males than homozygous gynoecious (FF). We bulk the seed of those selfs which are proven to be FF. Further increases of this seed can be made without selection for femaleness as long as no contamination occurs.

The two crucial features of this procedure are the checking of each selfed progeny for homozygosity and doing this under conditions which maximize the difference in male flower production between FF and Ff genotypes. For reasons which are not entirely clear, we have these conditions automatically in our greenhouse when we make plantings between August 1 and February 1. Without and chemical treatment, heterozygous gynoecious plants produce considerable numbers of males, while homozygous ones produce few, if any. For example, Ff plants of Marketmore flowering in December produce so many males that it is difficult to believe they can be carrying the gynoecious gene. Under these conditions if we grow as few as 4 plants per selfed progeny and find them all with few or no male flowers, the odds are 255 to 1 that the line is homozygous, and this can be established while the plants are still relatively small.

In the field we can differentiate homozygous from heterozygous gynoecious plants only by applying a chemical. We have had the best results with one application of GA4A7 at 50 ppm. Table 1 shows the dramatic differences in male flower production between homozygous and heterozygous plants with the same genetic background.

It is obvious from this table that it is easiest to distinguish FF from Ff plants with one GA treatment, since the Ff plants produced from 10 to 80 times as many male flowers as the FF. In treatments that produce more male flowers, the differences between FF and Ff become much narrower.

Table 1. The effect of male-inducing treatments on homozygous (FF) and heterozygous (Ff) gynoecious cucumbers in the field at Ithaca, N.Y., each value the average of 2 or 3 experiments.

Average Number of Male Flowers Per Plant
1 GA4A7 50 ppm
1 AgNO3 250 ppm
3 GA4A7 or 2 AgNO3
Genotype
FF
Ff
FF
Ff
FF
Ff
Tablegreen
0.1
8
2
40
4
37
Marketmore
2
40
10
42
19
57
Gy3
8
79
35
115
53
125
SR551
4
-
38
-
45
-

The final suggestion is to use some check plants that are known to be FF and some known to be Ff in any planting where one is determining whether selfed progenies are true breeding for the gynoecious character. In Table 1, the results for Marketmore in the FF columns are for Marketmore 70F. The results in the Ff columns are for Marketmore 70F x Marketmore 70. We find these good checks to use in testing homozygosity of slicers. For pickles we commonly use SR551F in comparison with SR551F x SR551.

4.Seed Development in Cucumbers after Harvesting when Immature

H.M. Munger

Departments of Plant Breeding and Vegetable Crops, Cornell University, Ithaca, NY 14853

Several years ago a cucumber plant in the greenhouse was killed accidentally while bearing a fruit pollinated about 3 weeks previously and from which viable seed was much desired. The green fruit was left in the greenhouse, exposed to natural light, and the seed when removed after about a month was plump and germinated normally. We assumed that photosynthesis in the green fruit had contributed appreciably to the seed development. To test this assumption and see if the result was repeatable, we conducted a small experiment in the greenhouse in the fall of 1977.

A number of fruits in a progeny derived from several backcrosses to Gy57 happened to be pollinated in the period October 14-21, mostly from October 16-18. These were harvested at intervals from 14 to 31 days after pollination and comparable fruits kept in a dark cupboard or on a bench in the greenhouse so that all had about the same temperature. Seeds were removed on December 28, washed, dried, counted, and weighed, with the results shown in Table 1.

Table 1. Seed development in cucumber fruits harvested when immature and held in light and darkness in the greenhouse, Ithaca, N.Y.

Date of Harvest
Days on plant after poll
Post harvest treatment
No. of fruits
Ave. No. seeds/fruit
Grams seed/fruit
Ave. wt. per seed (mg)
Nov. 2
14,15
Light
2
67
1.75
26
Nov. 2
15
Dark
1
63
1.48
23
Nov. 5,8
20
Light
2
78
2.15
28
Nov. 5,8
20
Dark
2
62
1.58
26
Nov. 8
23
Light
2
62
1.86
30
Nov. 8
23
Dark
1
53
1.37
26
Nov. 17
30,31
Light
2
146
3.69
28
Nov. 17
30
Dark
1
78
2.42
31
All
14-31
Light
8
88
2.36
28
All
15-30
Dark
5
63
1.68
26

All seeds appeared to be plump and normal regardless of treatment. Exposure of fruits to light gave consistently larger seeds but the difference was much less than anticipated, especially for the more immature fruits. Similarly, leaving fruits on the plants for 3 or 4 weeks instead of 2 had surprisingly little effect on seed size. These factors led to somewhat greater differences in number of seeds per fruit than in size of seed, but the effects could hardly be called striking when one looks at the seeds themselves or the data.

We have used this information to great advantage in subsequent years. We can pollinate later in the season and harvest the immature fruits when frost threatens, letting them ripen for several weeks in the greenhouse. In a greenhouse generation, we harvest the late pollinated fruits after 2-3 weeks, reduce problems of insects and disease, and release space earlier for a new crop.

5.Horseradish Seed Production

Michael Burke and A.M. Rhodes

Department of Horticulture, University of Illinois, Urbana, IL 61801

The following method is used to produce horseradish plants from seed in the breeding program at the Agricultural Experiment Station, University of Illinois. Harvest the main root in late October of early November. Cut the root about 2-4 inches from the crown. Trim off leaves, but do not cut into the crown. Store the crown roots in plastic bags at about 4 degrees Celsius. Most crowns will flower after about 2 months' cold treatment, but we can store the crown roots for about 6 months. Around April 23 the crowns are removed from storage and planted in large pots or cans in the greenhouse. Planting involves placing the crown in the bottom of the container and covering the crown with soil.

Plants will flower about May 23 plus or minus 5 days. During flowering, inflorescence of different cultivars are shaken together to provide cross pollination. During this period, a few insects, especially an unidentified fly, are active among the flowers and apparently aid in pollination. About 3 weeks after pollination, seeds start to turn brown and the pods begin to dry. Delaying harvest past this time can result in seed loss due to pod shatter. A fertile pod will contain 1-6 seeds, though 2-4 are normally produced.

At harvest, seeds are immediately planted in vermiculite. Seeds germinate in 3-4 days. About 7-10 days after germination, seedlings are transplanted to Jiffy-7 peat pods. Seedlings remain in the greenhouse for about 3 weeks, then moved outdoors. About mid-August the plants are transplanted to the field and given excess water. During dry conditions a second watering may be necessary. These plants remain in the field for about 14 months. They are then dug and evaluated. About 15-20% of the plants are selected for further evaluation.

6. Effect of nor in Different Tomato Hybrids

J. Farkas

Vegetable Crops Research Institute, Kecskemet, Hungary

Effects of some alleles controlling foliage, fruit shape and ripening in tomato were studied on shelf-life and quality in hybrid combinations with nor.

The hp, og and hp-og strains are isogene analogues of the variety K. 600; the strain nor was kindly supplied by Dr. E.C. Tigchelaar, Purdue University, IN.

The percentage of rotten fruit 25 days after initial ripening indicated that nor affected favourably vine storage in every hybrid combination, especially crossed by the square fruit type (symbolized as Sqr) (Table 1).

Genotype
Mean fruit weight, g
% of rotten fruits in field
% of rotten fruits - 4 weeks storage
% of rotten fruits - 8 weeks storage
+/+
47
8.6
97.3
100.0
Sqr/Sqr
40
2.5
56.7
99.2
(c x nor)F1
61
1.8
61.2
93.8
(el x nor)F1
50
1.9
70.5
95.3
(Sqr x nor)F1
44
0.1
22.5
70.5
(hp x nor)F1
55
1.3
43.2
90.6
(og x nor)F1
61
1.6
60.4
92.0
(hp, og x nor)F1
57
1.1
53.1
93.1

Healthy fruits harvested in red ripe stage were stored at room temperature (20 degrees Celsius). The storability of (Sqr x nor)F1 is remarkable; hp also has a favorable effect as stated by Kopeliovits et al., 1979, Euphytica 28: 99-104.

Flavour, however, needs improvement absolutely in nor hybrids as indicated by tasting after 4 weeks storage and the sugar-acid ratio above 9.

Genes affecting pigment accumulation do not improve colour visibly when in heterozygous state. Fruit color differences are only significant between (hp, og x nor)F1 and (c x nor)F1, the latter of small foliage (Table 2).

Genotype
Colour Agtron %
Sugar/acid ratio
Flavour subjective scoring 1-5
+/+
34.9
8.3
4.5
Sqr/Sqr
35.8
8.8
1.4
(c x nor)F1
42.3
9.3
3.2
(el x nor)F1
35.3
13.2
2.1
(Sqr x nor)F1
39.2
10.0
1.0
(hp x nor)F1
36.7
11.4
2.8
(og x nor)F1
34.6
9.7
3.1
(hp, og x nor)F1
31.0
12.5
2.6

Based on results a (ms, Sqr x nor)F1 hybrid can be taken into consideration for fresh market or machine harvesting. The control of fruit rot pathogens at the end of the season still has to be solved.

7. Uncatalogued Vegetable Varieties Available for Trial in 1981

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 on source, the address is given only for the first.

8. Stocks Desired

Request from: Warren S. Barham, Dept. of Horticultural Sciences, Texas A&M University, College Station, Texas 77843.

I am initiating research work on watermelon and squash. The usual needs for weed control, quality product at the desired season, disease and insect control have a high priority. We also need varieties possessing the following characteristics.

  1. Adapted to partial mechanical harvest.
  2. Tolerant to heat and cold, particularly germination and early seedling development.
  3. Tolerant to saline soil and irrigation water.
  4. Concentrated production (this can be considered part of item 1).
  5. I will add three diseases which appear to warrant special consideration:
    • Watermelon mosaic virus (both squash and watermelon)
    • New races of fusarium wilt and anthracnose in watermelon

 

Request from: E.A. Kerr, Horticultural Experiment Station, Box 587, Simcoe, Ontario N3Y 4N5.

For: 'Improved Bay State' tomato.