Résumé
Cotton production in Thailand has been decreased by nearly 50% over the last fifteen years. The cotton bollworm, #Helicoverpa armigera# Hubner is the key pest in Thai cotton cropping system. One strategy to circumvent this problem is to transfer to cotton plants genes encoding for #Bacillus thuringiensis# endotoxins which have been identified as very toxic towards this insect. Techniques were developed for embryogeni callus induction, transformation and regeneration of Sri Somrong 60, a Thai cotton variety. Somatic embryogenesis was obtained by culturing hypocotyl explants on to zeatin and NAA containing MS medium and subculturing on to hormone free medium. This method yielded 23-50% embryogenic callus induction. Transformation of Sri Somrong 60 with synthetic crylA(b) gene was accomplished by using #Agrobacterium tumefaciens# strain C 58: pG2260. The selection of resistant calli which were obtained at frequencies varying from 3 to 50%, was accomplished on kanamycin containing medium. The molecular analysis of recovered plants showed the integration of the transferred gene. Bioassays conducted with leaves of different transgenic plant lines showed different level of resistance towards #Helicoverpa armigera# first instar larvae. The association of B.t genes with other tolerance characters existing in the cotton germplasm is in progress using conventional breeding techniques. (Résumé d'auteur)