Cucurbit Genetics Cooperative Report 1:23-24 (article 22) 1978
O. L. Chambliss and J. D. Norton
Auburn University Agricultural Experiment Station, Auburn, AL 36830
A bulk population of cucumber beetle resistant watermelon has been developed from resistant single plant selection grown in minimum isolation and allowed to open-pollinate for three generations.
The original population was grown at the US Vegetable Lab., Charleston, S.C. Single resistant plants were selected in greenhouse screening tests, using banded cucumber beetles, Diabrotica balteata, from F2and backcross generations of crosses between the resistant ‘Sugar Loaf’ and the following susceptible cultivars: ‘Charleston Gray’, ‘Charleston Gray 133’, ‘Crimson Sweet’, ‘Graybelle’, ‘Sugar Baby’, ‘Black Diamond’, ‘Cobb Gem’, ‘Desert King’, ‘Desert Queen’, ‘Wilson Sweet’, ‘Orange Flesh Tendersweet’, ‘Market Midget’, ‘New Irish Gray’, and ‘Miss 1717’. Genetic analysis indicated that resistance was controlled by a single recessive gene.
The procedure by which the bulk population was developed:
- 1st year – Single resistant seedlings (approximately 40 plants) selected in F2 and planted in minimum isolation plot approximately 6×9 m, protected by similar size plots of cantaloupe and cucumber. O.P. seed were bulked (75/fruit).
- 2nd year – Bulk planted (approx. 100 plants) in isolation. O.P. seed were bulked (75/fruit).
- 3rd year – Bulk planted (approx. 200 plants) in isolation. O.P. seed bulked (150/fruit) to form existing bulk population.
During the summer and fall of 1977, the existing bulk population was evaluated for horticultural characteristics and cucumber beetle resistance. Fruit size was large, generally; many would be classed in the 20 kg range. Fruit types were highly variable in shape and color ranging from round to oblong and from gray to dark green, both solid and striped, although many were oblong, gray types. Seed type varied from very small to large, and from dark brown to white. Flesh type was generally good in appearance. Most fruits had a deep red flesh, although a few were observed with white heart. Of the approximately 200 plants observed, one plant each produced yellow and orange flesh. Soluble solids determined on approximately 1/4 of the population ranged from 9.4 – 12.8%. Only 2 plants of these produced fruits less than 10% solids. Average soluble solids for this sample of the population was 11%.
Resistance to spotted cucumber beetles, Diabrotica undecimpunctata howardi, was tested on seedlings from bulked seed of this same population. Tests were conducted in greenhouse cages, using approximately 1 insect per seedling. Seedlings were rated qualitatively as either resistant or susceptible when the susceptible check, ‘Charleston Gray’ was exhibiting severe damage. The resistant bulk was as resistant or more so than the original source of resistance, ‘Sugar Loaf’ as shown below:
Table 1. Resistance of seedlings to spotted cucumber beetles.
No. of Seedlings |
|||
Population |
Resistance |
Susceptible |
% resistance |
| Bulk – 77 | 145 | 14 | 91.2 |
| Sugar Loaf | 46 | 5 | 90.2 |
| Charleston Gray | 0 | 44 | 0 |
Thus, a variable population of cucumber beetle resistant watermelons has been developed from which breeders can select desirable types directly or use as a source of cucumber beetle resistance in breeding programs.