Published online by Cambridge University Press: 19 September 2011
The susceptibility of 23 cotton genotypes to spotted bollworm, Earias vittella, was studied under natural infestation during 1977 and 1978 rainy season at Delhi, India. There were substantial differences in bollworm damage and larval population in different genotypes. Damage in shed squares and bolls was higher than in green bolls picked up from the plant. The damage/larval population in the less susceptible cultivars (Hindiweed, XG-15, HR-26 # 8XH · HG-6-IN and Sanguineum) was lower than in the susceptible check (BJR) and the trial mean. The differences in susceptibility were more pronounced at the moderate damage levels and that the damage in less susceptible cultivars increased or decreased according to the insect pressure.
There were significant differences in the gossypol, tannins, moisture, phenols and sugar content among the genotypes tested. Gossypol, tannins and moisture content of bolls and squares were negatively correlated with bollworm damage and larval population. Free phenols showed negative, but lower correlation coefficients with bollworm damage. Sugars contributed towards susceptibility while nitrogen content of bolls did not show any effect on bollworm damage. The less susceptible cultivars had higher amounts of gossypol and tannins. Some genotypes showed ovipositional non-preference because of smooth leaves.
Many factors appeared to influence the genotypie susceptibility to spotted bollworm, of which gossypol, tannins and ovipositional non-preference (due to smooth leaves) were the major factors. Gossypol and smoothness are genetically inherited and can be manipulated through crop improvement. The rating of the number and size of pigment glands on the calyx tubes and hairiness on the under surface of leaves can be used as important marker characters in breeding for spotted bollworm resistance.