IMPACT OF Bt- COTTON ON WHITEFLY, Bemisia tabaci (Genn.) POPULATION

Genetically engineered cotton genotypes, Gossypium hirsutum L., (Bt-121, Bt-196, Bt-313, Bt-333, Bt-496, Bt- 703, Bt-802, Bt-1524, Bt-3701, Bt-W1) were evaluated for their resistance against whitefly, Bemisia tabaci (Genn.), during the cropping seasons 2008 and 2009. In 2008, Bt-496 showed highest susceptibility to B. tabaci (4.52 population/leaf) followed by Bt-121(3.55 population/leaf) and Bt-3701 (3.19 population/leaf) while all the remaining varieties were statistically at par having minimum population per leaf ranging from 1.97 to 2.75. In 2009, Bt-496 showed highest susceptibility to B. tabaci (4.97 population/leaf) followed by Bt-333 (4.25population/leaf) while all the remaining varieties were statistically at par having population ranging from 2.09 to 3.59 per leaf except Bt-703 which showed highest resistance to B. tabaci (1.41/leaf). Four physico- morphic characters of the leaves viz., gossypol glands, hair density, hair length and lamina thickness were also studied of the subjected cotton genotypes. In 2008, lamina thickness and gossypol glands were positively correlated with mean B. tabaci population/leaf (r = 0.66; r = 0.67 respectively) whereas in 2009, hair length and gossypol glands showed negative and positive correlations respectively (r = -0.65; r = 0.78). Minimum temperature and wind speed were negatively correlated while sunshine had a positive impact on B. tabaci population.