Vegetable Improvement Newsletter No. 1, January 1959

Compiled by H.M. Munger, Cornell University, Ithaca, New York

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1. An Asparagus Variety Cross

T.M. Currence

University of Minnesota, St. Paul 1, Minnesota

If two asparagus varieties were developed in such a way that they carried diverse genes for vigor, it would be expected that a cross between them might show heterosis for yield or for size of spears. The variety K.B.F. is from England, and California 500 was developed in California. Insofar as their breeding is described in the literature, it seems possible that some amount of inbreeding occurred in the pedigree of each. The possibility of the F₁ Cal.500 x K.B.F. showing heterosis has been tested. Six different crosses between individual plants were made and the resulting progenies have been grown for two years in comparison with the parent varieties. The parents, the mean of six crosses and the two best crosses, gave the following annual means.

Treatment	Spear wt. (g)	Yield (lb/A)
Cal. 500	12.5 ± 1.07	2451 ± 158
K.B.F.	16.5 ± 1.07	4480 ± 158
Cal. 500 x K.B.F. - 6 crosses	15.7 ± 0.44	3870 ± 65
Best spear size - 6 crosses	18.5 ± 1.07	4236 ± 158
Best yield - 6 crosses	14.5 ± 1.07	4298 ± 158

The six crosses exceed the average of the parents in both spear size and yield, In neither, however, does it exceed the better parent so that the phenomenon of heterosis was not shown. One cross was possibly superior in spear size with the difference being 2.0 g which is significant at approximately the 10 percent level. None was superior in yield. An obvious conclusion is that maintaining the identity of individual plant crosses might enable the breeder to recognize superior material for parental stock, but it seems unlikely that the first generation of a variety cross will average an improvement over a good parent.

It is regrettable that the identity of the original 6 K.B.F. and 6 Cal. 500 plants was lost and the individual crosses cannot be repeated. Remnant seed of the best spear size combination, however, has been planted resulting in about 50 seedlings. These are available if anyone cares to use them in breeding work.

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2. Cucumber Mosaic Resistance in Hawaii

J.C. Gilbert

University of Hawaii, Honolulu 14, Hawaii

Breeding work with cucumber lines possessing varying degrees of resistance to mosaic has been carried on at the University of Hawaii Agricultural Experiment Station since 1950. Among the several strains of mosaic observed here, there has occurred at least one severely distorting and stunting virus which has been able to produce marked symptoms on cucumber varieties released as "resistant" to cucumber mosaic on the mainland U.S.A. Under some conditions, completely susceptible lines are killed following early exposure to this virus, while the partly resistant lines remain stunted with crinkled, distorted leaves and fruit, and no marketable yield.

Although several generations of cucumbers per year can be grown in Hawaii and thousands of seedlings were screened for resistance to this virus, only one selection was found whose progeny could not be distorted or stunted by the disease. It was derived from a breeding line received from Cornell at the start of the program and differed from the parent line not only in having improved resistance to mosaic here but in several fruit characters as well. Breeding lines derived from this selection were improved for horticultural qualities with crosses made to recent Cornell and South Carolina lines and the extra degree of resistance recovered in several cases. A hybrid made in 1958 between two such resistant lines has outyielded all commercially available hybrids sold as mosaic resistant on the mainland. Crosses made with only partial resistance in one parent have not shown this particular degree of resistance in the F₁. When an F₁ hybrid is made with a susceptible line, the plants are vigorous but the resistance to mosaic is lowered too much to be of value here.

This distorting and stunting cucumber mosaic found in Hawaii was passed through partially resistant cucumber hosts in the 1958 tests and a new strain of the virus emerged which can now produce fairly severe symptoms even on the previously highly resistant lines described above. No such symptoms had been seen previously in six years of these tests with the highly resistant lines. When we used susceptible cucumber varieties like Colorado or Straight-8 as a source of inoculum for a breeding trial, we had no such trouble with a breakdown in the resistance of our better lines.

Farmers in Hawaii grow cucumbers throughout the year and usually plant Burpee Hybrid. In some districts they are complaining of increasing symptoms of mosaic in this hybrid. Our experience with the use of inoculum taken from partially resistant plants suggests a possible explanation for this difficulty. It also suggests that trying to breed for cucumber mosaic resistance in Hawaii may be a hazardous procedure at best.

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3. Transfer of Bush Habit from Cucurbita pepo to Cucurbita moschata

H.M. Munger

Cornell University, Ithaca, New York

Crosses between C. pepo and C. moschata have been reported a number of times but, to the best of my knowledge, a transfer of desirable genes from one species to the other has not been reported. Wall (Proc. A.S.H.S. 63:427-430) made the cross Yankee Hybrid (C. pepo) x Butternut (C. moschata) and backcrossed the F₁ to Butternut. In this backcross progeny two bush plants appeared in 1954 and open-pollinated seed was saved from them. Bush plants appeared when this seed was planted in 1955, and three of them were backcrossed to Butternut for the second time. In the following years third and fourth backcrosses have been made.

Most of the bush segregates are not as strictly determinate as in the Yankee Hybrid parent but have short internodes in the early stages, set their fruit close to the crown, and later send out runners of varying lengths. Some of the progenies are now virtually indistinguishable from Butternut in fruit type, but the ones with the shortest vines are not yet that good in fruit type. Fertility seems nearly normal in most of the present progenies. Considerable earliness has been carried over from theC. pepo parent in some progenies.

Parental material is available to breeders who may be interested in transferring bush habit or other characters toC. moschata varieties.

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4. Suggestions for Packaging and Marking Trial Samples

E.W. Scott

Joseph Harris Company, Inc., Rochester 11, New York

For ease of filing and sowing, all seeds should be in paper envelopes of adequate size so that envelopes can be re-closed after planting. Cloth bags are hard to file and tags are difficult to read when filed. Opening and closing and sowing from cloth bags in the field is cumbersome.

Each sample should have the following information written or printed clearly on the envelope -- type of seed; name or number of sample; lot number (if any) from which sample was taken; name of company or institution putting sample out; name of individual in an institution; type of treatment on seed sample, and what standard variety, or varieties, the sender would like to have the sample compared.

If the sample is extremely small, number of seeds in sample is important. If sample is low in germination this should also be noted. If sample is resistant to disease, this should be noted.

Where large numbers of samples are to be filed, sorted and arranged for trial, this information on the envelope will save a good deal of time in looking up correspondence.