ABSTRACT
The population and damage by aphid, Lipaphis erysimi (Kalt.) in Brassica spp. is highly variable across seasons and regions, wherein screening of rapeseed-mustard genotypes under natural infestation conditions has not been rewarding for aphid resistance. Since no reliable screening technique is in place, we developed and evaluated various screening techniques to differentiate diverse mustard genotypes for resistance to L. erysimi under field conditions. Artificial infestation at bud formation stage with 20 mixed stage aphids pinned with bell pins on the top third branch near inflorescence was found most appropriate and effective for establishment of aphids at inoculation site. Evaluation of mustard genotypes under multi-choice natural infestation revealed maximum variability in L. erysimi resistance indices, but plot cage artificial screening technique was found appropriate over natural infestation for multi-choice assays. Genotypes Heera and PDZM 31 showed susceptible to highly susceptible reaction against L. erysimi under all the artificial infestation screening techniques. However, PM 30, PM 21, Pusa Bold and Pusa Vijay displayed variable resistance reactions under different screening techniques. Although no-choice twig cage and plant cage techniques showed significant differences in test mustard genotypes for various aphid resistance indices, the twig cage technique revealed maximum variability and could differentiate them at slightest variation in levels of tolerance/susceptibility to L. erysimi. The rate of L. erysimi multiplication on test mustard genotypes was highly variable under plant cage as compared to twig cage. The twig cage technique also successfully differentiated the double low erucic acid and total glucosinolate, single low erucic acid, and conventional varieties with high erucic acid and total glucosinolate groups of mustard genotypes for L. erysimi resistance. The multiplication rate and ease in scouting of aphids, easy handling and cost of the cage, and natural plant growth conditions are some of the most favourable factors, suggesting twig cage technique more précised, realistic, economical, and efficient for artificial screening of rapeseed-mustard for resistance against the aphid L. erysimi infestation
ABSTRACT
Adequate expression of Bt (Bacillus thuringiensis) toxins and purity of seeds of Bt-transgenic cottons are important for controlling bollworms, and thereby increasing the cotton productivity. Therefore, we examined the variability in expression of Bt toxin proteins in the seeds and in leaves of different cotton (Gossypium hirsutum (L.) hybrids (JKCH 226, JKCH 1947, JKCH Durga, JKCH Ishwar, JKCH Varun KDCHH 441 and KDCHH 621) expressing Bt toxins in F1 and F2 generations, using bioassays against the cotton bollworm, Helicoverpa armigera (Hübner), and the lateral flow strip (LFS) test. Toxicity of Bt toxin proteins in the seeds of Bt-transgenic cottons to H. armigera correlated with their toxicity in the leaves in one-toxin Bt cotton hybrids. The Bt-F1 and Bt-F2 seeds of JKCH 1947 were more toxic to H. armigera than those of JKCH Varun seeds. The seeds and leaves of F1s showed greater toxicity than the F2 seeds or leaves of one-toxin (cry1Ac) Bt cotton hybrids. However, no significant differences were observed for the two-toxin (cry1Ac and cry2Ab) hybrid, KDCHH 621. Toxicity of leaves to H. armigera increased with crop age, until 112 days after seedling emergence. The Bt trait purity in F1 seeds of four two-toxin Bt cotton hybrids ranged from 86.7 to 100%. The present study emphasizes the necessity of 95% Bt trait purity in seeds of transgenic cotton for sustainable crop production.