Innovative on-plant bioassay method for selection of superior genotype/cultivar/event against pink bollworm, Pectinophora gossypiella (Saunders) in cotton in protected screen house condition

Abstract

Several methods have been advocated for screening of potential transgenic events that use either diet incorporation of toxins or excised plant parts expressing the pure protein (toxin) against insect pests of crops. However, considering the field level variations in transgenic plant expression due to abiotic environmental factors; mainly the temperature and moisture stress, it was a long felt need for development of a bioassay method that can be readily employed under field conditions. Here, we present a simple, rapid, relatively stable and reliable method of on-plant bioassay for screening of genotypes or transgenic events against pink bollworm, the major insect pest of global significance to cotton. The proposed method involved releasing neonate larvae of pink bollworm on approximately 12–15 days old undetached bolls of non-Bt and Bt (Bollgard I and Bollgard II) cotton plants and covering them with a kite paper bag to prevent larval escape. The tagged bolls were kept undisturbed for next 21 days. After completion of this period the observations on larval entry holes, locular damage, exit holes and per cent damaged bolls were recorded in each case. The experiments were repeated for two consecutive cotton cropping seasons of 2018–19 and 2019–20 on early (100 DAS) and late (150 DAS) formed bolls on cotton plants. Successful larval establishment and boll damage across the stages observed in non-Bt cotton plants compared to Bt cotton plants indicated the adequacy of proposed on-plant bioassay method. The late formed bolls exhibited relatively higher damage compared to early formed bolls in the plants that carrying Bt genes, indicating temporal decrease in toxin expression due to plant aging. This method being relatively easier and reliable, will be highly useful to the breeders, entomologists and seed producers in screening of superior transgenic material against pink bollworm in cotton.