Cucurbit Genetics Cooperative Report 2:16-17 (article 10) 1979
Investigations of the Effects of Plant Type and Morphology of the Cucumber on Infestation by the Pickleworm, Diaphania nitidalis Stoll
Terry Lane Pulliam and R. L. Lower
Department of Horticultural Science, North Carolina State University, Raleigh, NC 27650
E. V. Wann
U. S. Vegetable Laboratory, USDA, SEA, Charleston, SC 29407
Seven plant types of 'Addis', a pickling cucumber cultivar, five plant introductions, tetraploid lines, and other lines were evaluated for resistance to the pickleworm. Oviposition cage, screenhouse, greenhouse, and field experiments tested either the oviposition response of adults and/or the feeding response of larvae.
As expected, none of the plant types or plant introductions tested expressed immunity to infestation by the pickleworm, either to the adult in oviposition or the larvae in feeding.
Glabrous lines, whether on 'Addis' or another background and whether bitter or nonbitter, were consistently lower in number of eggs/cm2 than other pubescent lines in oviposition experiments. When glabrous 'Addis' leaves and pubescent 'Addis' leaves were tested in the same cage, the glabrous leaves were significantly lower in number of eggs/cm2 than the pubescent leaves. When glabrous 'Addis' leaves and pubescent 'Addis' leaves were tested in separate cages, significantly fewer eggs/cm2 were oviposited on glabrous leaves. Therefore, it was concluded that the glabrous character was responsible for the nonpreference of the moth for oviposition on these leaves. When glabrous 'Addis' leaves were the only oviposition substrate in the cage, the moths laid fewer eggs on these leaves. Eggs were deposited on the crinkled serrate edges and next to the veins of the glabrous leaves. This supports the theory that a tactile stimulus is necessary for normal oviposition. Also, the tetraploids, which were visibly more pubescent than diploids, had generally higher numbers of eggs/cm2 than the diploids.
In the greenhouse and screenhouse experiments, the glabrous lines tended to be very heavily damaged by feeding, to have surviving larvae with higher mean weights, and to have lower fresh plant weights. This suggests that larvae tended to feed more easily and quickly on plants without trichomes. Unfortunately, the feeding damage results for the tetraploids are inconsistent, and the relationship between levels of feeding is unclear.
PI 269480, West Pakistan, tended to have less damage, smaller larvae, and higher plant weights than other lines, PI 390254, Japan, which was selected in experiments in Charleston in 1977, gave results similar to PI 269480.
In the field experiment, results tended to show glabrous lines were not as heavily damaged as pubescent lines. The three glabrous lines, 'Addis' glabrous, 'Addis' glabrous nonbitter, and NCSU 75-834-5, were lower than other lines in damage ratings and in percent damage ratings. Glabrous lines also had higher numbers of undamaged fruit per hill than other lines. The two tetraploid lines used in the field experiment were not as heavily damaged as about half the pubescent lines.
The results of the field experiment were most closely correlated to those of the oviposition experiments, where glabrous leaves were not preferred as an oviposition substrate. Therefore, the resistance of glabrous lines in the field can be attributed to a nonpreference of the adult pickleworm for glabrous plants for oviposition.
In relatively isolated plots, glabrous lines were nearly free from damage while other lines were heavily damaged.