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Vegetable Improvement Newsletter No. 2, February 1960
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Compiled by H.M. Munger, Cornell University, Ithaca, New York

1. Interaction of Snap Bean Varieties with Fertility Rates

Dean E. Knavel and Donald J. Cotter

University of Kentucky, Lexington, Kentucky

Snap bean variety trials conducted the past several years indicated the existence of significant variety-fertility interactions for several varieties. It appears that the fertility status of the soil would be an important factor to be considered in snap bean breeding and variety testing. Snap bean variety B-3370 yielded high regardless of the fertility level, while yields of Topcrop, Wade, Improved Supergreen, and several other varieties increased with a fertility increase.

2. Induction of Staminate Flowers on Gynoecious Cucumbers

C.E. Peterson

Department of Horticulture, Michigan State University, East Lansing, Michigan

Field experiments in 1958 indicated that staminate flowers developed on some genetically gynoecious plants following two or three foliar applications of 250 ppm gibberellin A3. An F1 progeny from gynoecious x predominantly female which produced 100 percent gynoecious plants in the field in 1958 was used in greenhouse experiments that fall and winter. Staminate flower production was increased as concentrations increased from 250 to 1500 ppm and as the number of applications was increased from one to four. Plants receiving four weekly applications of 1500 ppm developed an average of seven nodes per plant bearing staminate flowers. No staminate flowers were borne on the untreated plants. The induced staminate flowers produced abundant pollen and many successful pollinations were accomplished.

One gynoecious line, M.S.U. 713-5, inbred for three generations by means of selfing with pollen from induced staminate flowers, appears to be homozygous gynoecious under field conditions here. A high degree of vegetative tolerance to gibberellin and a wide range of effective induction treatments were observed. In the case of M.S.U. 713-5 and other gynoecious lines two, three or four foliar spray applications of 1500 ppm gibberellin A3 produced plenty of pollen for normal seed production. M.S.U. 713-5 was grown in two rows in a 12 x 80 foot isolation cage provided with a nucleus box of bees. One row of 74 plants was untreated and the other was used to determine the most effective number of 1500 ppm applications for adequate pollen production. Foliar applications were begun at the second true leaf stage and repeated at weekly intervals up to four times. Staminate flowers per one hundred nodes were 9, 45, 66 and 71 respectively for one, two, three and four applications. No staminate flowers were found at the more than 2000 nodes examined on control plants. The seed yield of 4.2 pounds from this cage indicates that gynoecious lines can be increased under field conditions by two or three weekly foliar applications of gibberellin at 1500 ppm.

This method of maintaining the female line has the obvious advantage of eliminating the necessity for rogueing in hybrid seed production. However, in crosses of gynoecious x monoecious thus far observed the F1 is neither gynoecious or predominantly female with only the first two to four nodes bearing staminate flowers. Pollen production from such hybrids will not be adequate for fruit production in commercial fields. Although genetic data is incomplete, it appears that it will be necessary to use a heterozygous line for the female parent or to blend seed in order to ensure ample pollen production.

3. Testing for Self-incompatibility in Brassicae

D.H. Wallace and D.J. Thompson

Department of Plant Breeding, Cornell University, Ithaca, New York

The traditional method of measuring the intensity of the self- incompatibility reaction in cabbage and broccoli has been to determine the average number of seeds obtained for each pollinated flower or for each pod set. The recent demonstration that self-incompatibility of Brassicae is sporophytically determined (D.R. Sampson. 1957. The genetics of self- and cross- incompatibility in Brassicae oleraceae. Genetics 42:253- 263) rather than gametophytically, provides another means of assaying the incompatibility reaction. The assay is based upon two distinct differences between the gametophytic system, which does function in Solanaceae, the legumes, and numerous fruit crops, and the sporophytic system. These differences are: 1. Whereas in the gametophytic system the reaction of a given pollen grain is dependent upon the particular (S) allele carried by that pollen grain, in the sporophytic system the reaction of a pollen grain may be independent of the specific (S) allele carried by the pollen grain but is definitely dependent upon the complete (S) allele genotype of the plant (sporophyte) producing the pollen. This means that all pollen from a given plant or sporophyte will react alike when placed upon the stigma of any one plant. 2. Whereas in the gametophytic system pollen grains germinate and the pollen tubes grow through the style at rates depending upon the presence or absence of incompatibility, the sporophytic system is characterized by failure of well defined pollen germination. Very short pollen tubes may be produced but these tubes will not enter the stigma and the contents of the pollen grain will not be emptied into the pollen tube.

The test for incompatibility reaction is conducted by pollinating stigmas of open flowers, taking care to see that an abundance of pollen is placed upon the stigma. The day following pollination, the stigmas are pinched off with a pair of forceps and placed in a fixative composed of three parts absolute alcohol to one part glacial acetic acid. After being in the fixative for at least one-half hour the stigmas are placed upon a microscope slide and the head of the stigma is cut into four or five sections. Acetocarmine solution is dropped over the tissue slices, they are pressed beneath a slip cover and observed under the microscope. With compatible pollinations many long pollen tubes will be present and grains which have emptied their contents into the pollen tube will stain lightly as contrasted to those which did not germinate. With incompatible pollinations there will be either no pollen tubes at all or only very short tubes which will not be longer than about twice the diameter of the pollen grain. All pollen grains will be darkly stained.

This assay procedure has the advantage of immediate results free of the effects of subsequent disease or accidents which might prevent seed development. We have found that the results generally agree with seed set. By pinching off only the stigmas, seed development will be normal and seed counts can be made for the same pollinations.

4. Progress in Breeding Slicing Cucumbers for Resistance to Scab and Mosaic

H.M. Munger, D.H. Wallace, and R.E. Wilkinson

Cornell University, Ithaca, New York

The mosaic resistant slicer sent out for trial as 55-610 has been named Tablegreen and is being increased by a number of seedsmen in 1960. Scab resistance is now being added by backcrossing, and the first progenies homozygous for resistance derived from the 4th and 5th backcrosses to Tablegreen will be grown in 1960. It remains to be seen whether these progenies will be as similar in type to Tablegreen as one would expect or whether they will behave like Ashe and Fletcher, which seem to have shorter fruit than their recurrent parents even though backcrossed several times.

We have also added scab resistance by backcrossing to 52-55, a mosaic resistant slicer closely related to one parent of Tablegreen. In some plantings it looks very much like Marketer in color and shape, while under other conditions, which we cannot define, the fruit shows too much stippling. For this reason we have never offered the line for general trial. It does seem to have merit as a parent for scab and mosaic resistant hybrids. Fruit of this line appears to be as long as that of the recurrent parent. We shall be glad to send seed to any breeder who thinks the line might be useful to him. Just ask for some SR52-55.

5. Performance of Thaxter in 1959

R.E. Wester

USDA, Beltsville, Maryland

Thaxter, a new downy mildew-resistant baby lima bean released in 1958 by R.E. Wester of USDA's Agricultural Research Service at Beltsville, Maryland, and Robert C. Cetas of the Cornell University Agricultural Experiment Station continued to yield well under a wide range of growing conditions in 1959. In the 1959 National Lima Bean Trials, Thaxter outyielded Early Thorogreen in 25 out of 30 tests and Clark's Bush in 22 out of 30 tests. Seedsmen expect to have sufficient seed to meet the demand of processors for Thaxter in 1960.

6. Performance of Downy Mildew Resistant Fordhooks in 1959

R.E. Wester

USDA, Beltsville, Maryland

The three downy mildew resistant Fordhook lines USDA 156, 1556, and 1656 lacked the heat resistance of Fordhook 242 in the 1959 National Lima Bean Trials. In 22 trials, Fordhook 242 yielded 6593 pounds per acre of prime marketable pods while USDA 156, 1556, and 1656 yielded 4756, 4274, and 4849 pounds, respectively. Concentrated Fordhook yielded 4934 pounds per acre which was slightly higher than USDA 156 and 1656. At present 1656 appears to be slightly superior to 156 and 1556. This line might prove satisfactory if planted late so that the pods would set during the cool weather and mature their crop of pods during the downy mildew season.

7. "Slip Type" Muskmelon

W.A. Frazier

Department of Horticulture, Oregon State College, Corvallis, Oregon

A few reports have been received from the "slip type honeydew" lines sent out in 1959. We will appreciate further notes from those who planted this material. Because of extreme difficulty in securing selfs of these melons in the cool Western Oregon climate we have hesitated to release anything for preliminary seed increase. It is possible for us, on the other hand, to pick out selfed plants each year, because the homozygous golden skin, non-netted melon we plan to "fix" can be readily distinguished from a hybrid with any other type melon. By a slow process of isolation we have hoped to purify a line without artificial pollination. We would greatly appreciate any assistance that anyone can give us, however, in selfing a line or lines of this melon. Our objective has been a golden rind, slip-type, firm fleshed, essentially non-netted, early, melon with distinctly high soluble solids and good resistance to cracking. It has been interesting to note from our records that we have secured increasingly high readings for soluble solids over a period of seven years, with many melons now commonly showing 17% soluble solids. The first melons to reach 18% soluble solids content were noted in 1959.

8. Bitter Flavor in Peas

H.H. Marshall

Department of Agriculture, Experimental Farm, Brandon, Manitoba

Tests for resistance to Pythium seedling blight of peas at the Experimental Fann at Brandon, Manitoba, have shown that most peas that carry the "A" gene for the development of anthocyanin in leaf axils, flowers, seed coats or pods, also carry a high degree of resistance. In attempts to transfer resistance from Purple Pod to acceptable garden varieties it was found that the "A" gene, Pythium resistance, and a bitter astringent flavor were always inherited together.

This flavor is difficult and unpleasant to detect. After a few bitter peas have been sampled, the sense of taste does not respond to less bitter selections. Since the flavor in question is frequently due to tannins it was thought that its presence might be demonstrated by testing with a ferric salt. This proved to be the case and a quick method of determination was developed.

Five ml of a stock solution of ferric tartrate was placed in a test tube. Shelled peas were added to fill to the level of the solution. The tubes were then placed in a boiling water bath for two minutes. A total of 134 varieties were tested of which 38 had colored flowers. All of the latter group caused the solution to turn a dense purple color, whereas none of the white flowered types caused color to develop. These tests were conducted on immature peas. A similar test on 102 varieties of ripe peas required 10 minutes cooking but gave equally positive results.

The evidence of the presence of tannin suggests a possible reason for the strong linkage between color and bitterness in peas. While neither the tannin nor anthocyanin involved were identified, it is known that they have similar and sometimes almost identical structures. Presumably a plant unable to produce one may also be unable to produce the other. At least in 450 Plant Introductions and a few hundred plants from breeding lines, no exception has been found to the rule that colored peas are bitter but in varying degrees.

9. Inheritance of Radial Cracking in the Tomato

Paul Prashar Dharam and Victor T. Lambeth

University of Missouri, Columbia, Missouri

A study of the inheritance of radial cracking in the tomato was carried out in 1959 involving the progenies of two resistant parents, Glamour and NY55-542, and two susceptible varieties, Marglobe and Mosage. Comparisons made between the observed and theoretical means of the parents, F1, F2, and backcrosses indicated that cracking is dominant, but the dominance is incomplete. Various genetic models were set up and comparisons made of the observed and calculated frequency distributions. The best fit was obtained when it was assumed that there are two strong genes and two weak genes for cracking with interallelic interaction.

The results further indicated that all the varieties do not possess the same inheritance. So resistance may be increased by crossing two resistant parents or in some cases by crossing a resistant with a susceptible parent. It is evident from the study that cracking is a quantitative character and the inheritance involves several major and minor genes with un- identical effects.

10. Haploid Watermelons from Tetraploid Strains

O.J. Eigsti

Chicago Teachers College, Chicago 21, Illinois

Opportunity to build breeding stock of diploids that are very uniform is improved with the method of deriving haploids from tetraploid populations by self pollination among the tetraploids. If the tetraploid is a homozygous inbred line, the derived haploids will be similar in genetic nature. Thus, a hybrid between the haploid and tetraploid provides a triploid with 3 similar sets of chromosomes.

As the number of series of uniform strains with 2, 3 and 4 sets of chromosomes is built by extracting haploids, then the variations among triploids can be prepared. If one series is designated as a.a; a.a.a; and a.a.a.a, and the second series as b.b; b.b.b; and b.b.b.b, then triploids a.a.a; a.a.b; b.b.a; b.b.b; and the corresponding diploid and tetraploid strains can be compared for hybrid vigor and the dosage effects of two, three or four sets of genes.

(In this note monoploid is used for plants with one set of chromosomes derived from diploids, and haploid refers to diploids that arise from tetraploids by parthenogenesis. The word haploid differentiates such diploids from those obtained by inbreeding procedures.)

11. A Tractor-Mounted Sprayer for Inoculating

W.C. Barnes

Clemson College Truck Experiment Station, Charleston, S.C.

A tractor mounted sprayer for inoculating with fungus spores, bacteria or virus was constructed at this Station by Dr. Wayne R. Sitterly and G.L. Buckner, Jr. Pressure is obtained from an air compressor driven by the power-take-off. Various regulators make the applicator very versatile. Since construction plans will be published in the Plant Disease Reporter early in 1960, no others will be available. Plant breeders having to inoculate large numbers of plants in the field will find this inexpensive applicator a great help in obtaining uniform treatment in a short period of time; thereby increasing accuracy as well as saving labor.

12. Preventing Fruit Rots in Cucurbit Breeding

W.C. Barnes

Clemson College Truck Experiment Station, Charleston, S.C.

Various methods of preventing fruit rots in squash and cucumber breeding plots have been tried. Not any were entirely satisfactory, but several were helpful. Placing strips of old or salvage edge asphalt shingles under summer squash fruits has given good results, except when excessive rains washed soil on top of the shingles. Sheets of heavy aluminum foil about 10" x 15" placed under and over the southern side of cucumber fruits gave good results. Care must be taken to place foil in a position where rain water will drain out and reflections from the sun will not scorch fruits. Both of these are difficult to maintain as the fruits enlarge. "Safe and Dry" laminated paper appeared good for a few days but later proved more harmful than protective. A heavy laminated aluminum building paper has been used with slightly better results than the foil because it prevented the fruits from pocketing as they enlarged.

Placing 18" strips of black plastic or treated Kraft paper on each side of the row at lay-by time has proven quite successful in seed increase plots. About two trips over the plots to pick fruits that drop between the strips of mulch or on the outside will be adequate. The mulch is held in place by a little soil about every 10 feet. The vines quickly cover the plastic, hence the need for so little soil. The mulch also aids in the control of weeds, which tend to increase fruit rots, by keeping the surface of the soil wet longer following rain or heavy dew. The principal fruit rotting organism in this area is Pythium.

13. Ratings Scales for Characteristics Not Easily Measured

H.M. Munger

Cornell University, Ithaca, New York

In evaluating varieties and breeding lines, ratings are commonly used to record characteristics which are not measurable (e.g. disease resistance, quality) or for which measurement would be too time-consuming (e.g. color, shape) . A numerical rating can be written more quickly than a verbal description and can be treated statistically. A scale of 1 to 5 is often used. The purpose of this note is to point out the advantage of the 1 to 9 scale that Prof. Paul Work taught to his classes and which we have used extensively in vegetable work at Cornell.

In using this scale for the first time for a given characteristic, we think in terms of classes 1, 3, 5, 7 and 9, with 1 meaning very little or very poor, 3 poor, 5 fair or average, 7 good, and 9 very good. Then as poorer material is eliminated from the breeding program and experience permits greater discrimination, the intermediate values 6 and 8 come into use. The great advantage of this scale is that the intermediate values can be added without resorting to decimals or fractions.

We have occasionally deviated from the 1-9 scale and used 1-5. In these cases we have eventually found ourselves giving ratings such as 3.5 and 3.25. One hesitates to give the top rating of 5 very often and lines getting ratings in the lower half of the scale are not likely to be continued. Consequently most of the ratings eventually are either 3 or 4 unless decimal values are used, and two classes are hardly enough to describe the continuous variation encountered in most characteristics. Even with the 1-9 scale there are not too many choices since we find after a few years that most lines of continuing interest are getting ratings of 5, 6, 7, and 8, with only a few being rated 9.

One mistake we have sometimes made is to rate a series of characteristics in such a way that 9 is best for one while 1 is best for another. This can be avoided by naming the characteristics properly, for example disease resistance rather than disease, freedom from cracking rather than cracking, and firmness rather than softness. A high rating then denotes desirability in each case and ratings can be interpreted at a glance.