Resistance of cotton cultivars to cotton leafhopper, Amrasca biguttula (Ishida) and its association with some plant characters.

Results showed that the resistance rating obtained from previously identified materials conformed with this study except for four cultivars wherein reactions were complete deviation from the original rating. Various factors affecting variable plant, and insect interaction like location and screening techniques were believed to have caused these differences. Feeding and ovipositional antixenosis, and antibiosis were operating as mechanisms of leafhopper resistance as indicated by low insect counts, longer duration of nymphal stage, higher insect mortality, shorter adult longevity, and lower rate of population increase in resistant cultivars. In addition, nymphal emergence and rate of population increase were positively correlated to leafhopper counts while duration of nymphal period was negatively correlated to leafhopper counts in the feeding antixenosis test. The number of insects present in the cultivar therefore is a function of the combined effects influencing leafhopper population build-up. Likewise, higher damage threshold level was observed in resistant cultivars compared with UPL-C2 and DP 16. Highest damage threshold level was observed in A1a 894 (65) which was approximately 33 nymphs per plant at 75 days after plant emergence. Aside from the seedling stage, the cotton plant was also sensitive to leafhopper attack at 30 to 60 days after plant emergence. Hairiness as indicated by the length and density of trichomes on the lamina as well as on the veins were considered responsible for the resistance of cultivars A1a 894 (65), Ferguson Liza, Linea 17, Bayou 70, and ISA 205. In addition, gossypol, moisture and nitrogen contents did not show consistent pattern of relationships with resistance.