author(s)
KPM Dhamayanthi, K Rameash, A Manivannan, Annie Sheeba and S Abirami

abstract
Trichomes play a key role in imparting host plant resistance against important insect pests in cotton. They act as significant insect non-preference trait against the sucking pests of cotton thus decreasing the reliance on pesticides. In the present study, qualitative and quantitative analysis was carried out to find out the density of trichomes in Gossypium barbadense cotton. Qualitative grading was done based on the visual examination of the relative density of the abaxial trichomes and the total trichomes in a specific unit area were measured in each generation for the quantitative analysis. The presence of the trichomes in abaxial surface of the leaves, on the stem and branches in G. barbadense cotton were being taken for quantification. Significant variation was observed in number of leaf trichomes in four generations of three inter-mating crosses of G. barbadense. The segregating population studies reveals that variation for the hairiness character was not uniform in F₂ generation indicating the presence of the qualitative nature of the trait. Hairiness was very prominent in early days of the different generation of the crop and declined slowly as they approach towards maturity. A notable finding from the study is irrespective of the parents and generations, trichome population appears more in the apex region of the plants and when it goes down to the plant canopy it get gradually decreased. It is an evident that the genes responsible for hairiness is not get transferred and does not have any effect in the fashion of producing trichomes in different genetic backgrounds. The finding has broadened our knowledge in genetics of trichomes in cotton. In view of the resistance rendered by trichomes against the insect-pests, this study of genetics of leaf trichomes based on the relative distribution and density of the trichomes on the abaxial leaf surface is helpful in breeding cotton genotypes with specific reference to the reduced insect/pest population.