ABSTRACT
Since the introduction of Bt cotton, its cultivation expanded rapidly from 0.29 lakh ha in 2002-03 to 130.49 lakh ha by 2022-23. By 2015, over 95 % of the Bt cotton area consisted of BG II hybrids with stacked genes (Cry1Ac + Cry2Ab). This widespread adoption exerted significant selection pressure on pink bollworm (PBW), leading to field-scale resistance in India during 2010. Resistance was confirmed through bioassays of PBW populations across India, a process taking 21 days. A survey across 59 locations in India could showed higher boll occupancy of 2.56 in Nagpur and least of 0.71 in Uttara Kannada. Larval parasitoids Bracon lefroyi and Apanteles angaleti have been found actively associated with PBW. Conventional diet incorporation bioassay could show higher resistance in Nagpur strains to Cry1Ac (LC50 of 7.682 µg/ml) and Cry2Ab (LC50 of 12.574 µg/ml). This process typically requires 21-days and the proper Cry toxins hence go tedious and time consuming. For quicker detection of Cry toxin resistance in PBW, Simple Sequence Repeats (SSR) markers have been identified through Bulk Segregation Analysis (BSA) and found that the three SSR markers (notr15F and r15allR2; 164Pgcad5 F and 163Pgcad3 R; gF47 and gR47) were polymorphic between Cry1Ac resistant parents and bulks. Whereas, one SSR marker (gF47 and gR47) was polymorphic between Cry2Ab resistant parents and bulks. Among these specific markers gF47 and gR47 was common to depict Cry1Ac as well as Cry2Ab resistance. Further, the markers were validated in different life stages (larvae, pupae and adults) during 2023-24 with samples from 15 locations having history of reported resistance. Thus, Quick and highly reliable approach for detection of resistance in pink bollworms Indian strains to Cry toxins (Cry1Ac + Cry2Ab together) and /or Cry1Ac has been found through selected SSR markers, which is robust, faster and economical.