Morphological basis of resistance to spotted bollworm, Earias vittella (Fabricius) in Asiatic cotton

Abstract

Ten genotypes of Asiatic cotton, Gossypium arboreum, viz. C-353, G 17, G 33, AC-3545, LD 491, LD 575, B 11 A, SAG-BLY (Red), Sargosi and LD 694, were screened under epiphytotic conditions against spotted bollworm, Earias vittella, at the cotton farm of the Department of Plant Breeding and Genetics, Punjab Agricultural University, Ludhiana, India, and their morphological basis of resistance to spotted bollworm was studied. The plant characters examined were plant color, leaf shape, size and shape of bract, density of gossypol glands, nectaries, hair density and hair length. Hair density was positive (r = 0.81, P = 0.005) and significantly correlated with the number of eggs laid by E. vittella, whereas a significantly negative (r = –0.66, P = 0.038) correlation was obtained with gossypol glands. Similarly, correlation of larval population with hair density was significantly positive (r = 0.68, P = 0.030) and gossypol glands were negative (r = –0.63, P = 0.050) and significantly correlated with larval population. The R2 values, computed together for multiple regression analysis, indicated that the morphological plant traits, viz., gossypol glands and hair density, cumulatively contributed 67% and 50% variability in the egg and larval population, respectively. Genotype B 11 A, with the lowest egg and larval population, had a high number of gossypol glands, low hair density and smaller bracts and proved to be the best, followed by LD 491. Genotypes with low hair density, smaller bracts and a greater number of gossypol glands are desirable for low oviposition and larval population of E. vittella. These characteristics should be taken into consideration when planning a resistance breeding program against spotted bollworm in arboreum cotton.