Characterization of Bacillus thuringiensis from Cotton Fields and its Effectiveness against Spodoptera litura

Abstract

Cotton is a cash crop of many countries as it serves as a source of fiber, edible oil, and seedcake. It is grown in a diverse range of environment. Bacillus thuringiensis (Bt) is a gram positive bacterium found in different habitats but mostly found in soil. This bacterium produces endotoxin which is harmful for various insects. Numerous crystal-forming strains of Bt exist in nature, but not all of them are efficient against insect pests. Bt cotton is prevalent internationally because of less insect attack. The key objective of this research was to analyze different Bacillus thuringiensis isolates residing in soil of different cotton fields of Multan and Bahawalpur districts and to identify them on the basis of morphology. To attain this, different soil samples were collected from Multan (Gup wala, Mosey Wala, Taloki Wala, Hafiz Wala, Choudary Wala, Basti Mangla Mari, Sharkha Wala, Lawain Wala, Ghulamo Wala) and Bahawalpur district (Basti Deewan Wali, Check No 8, Basti Tariqabad, Basti Khaji Wala, Basti Khandin, Basti Rammo Wali, Sultanpur, Khurampur, Jahanpur). About 178 colonies of different bacteria from eighteen soil samples appeared on Nutrient Agar plates. The screening of colonies based on morphology yielded 18 colonies of Bt. We performed endo-toxin production experiment and confirmed the presence of parasporal crystals in identified B. thuringiensis colonies. Colony forming units of soil samples collected from Multan and Bahawalpur represented statistically significant results. Based on morphology, eight colonies of B. thuringiensis were confirmed out of eighteen colonies. Results of the current study revealed that out of 18 isolates, 8 bacterial isolates that were grown on the media had an increased elevation, a round, white, slimy morphology, and smooth edges. Toxicity test for resistance to cotton leaf worm second instar larvae revealed that two strains (BtS2, BtS7) of B. thuringiensis were toxic and showed 39.25% mortality. This study will help to identify the local Bt isolates that can be used for the indigenous insect pest control.