Endophytic establishment of native Bacillus thuringiensis strain in maize plants and its efficacy against Spodoptera frugiperda (J.E. Smith) (Lepidoptera: Noctuidae)

Abstract

Abstract Background Bacillus thuringiensis (Bt) is known as the most successful microbial insecticide worldwide used against lepidopteran insect pests in agriculture. Native Bacillus isolate VKK5 showing insecticidal activity against Spodoptera frugiperda (FAW) (J.E. Smith) (Lepidoptera: Noctuidae) was characterized as B. thuringiensis (BtVKK5) on a morphological and molecular basis. Recent research has shown that Bt can be established as an endophytic organism for controlling insect pests. The present work aimed at assessing the colonization of BtVKK5 as an endophyte in five maize cultivars by seed treatment (ST), soil drenching (SD), foliar application (FA) and combination of all methods (ST + SD + FA) and its bioefficacy against neonates of FAW. Results Establishment of inoculated BtVKK5 as endophytes in five maize cultivars, viz. Pusa HQPM7 Improved, Pusa Jawahar Hybrid Maize 1, Pusa Vivek Hybrid 27 Improved (PVH27I), Pusa HQPM5 Improved and DMRH 1301, was confirmed by re-isolating from the leaves of the plant on ampicillin-selected agar plates. Estimation of colony-forming units per gram of leaf showed that there was a significant difference in colonization of the Bt strain among maize cultivars by different inoculation methods. The colonies were further substantiated by the amplification of cry1A and cry1E genes. Bioefficacy studies showed the highest mortality (50%) in the ST + FA + SD inoculation method, followed by ST (40%) in PVH27I. Moreover, growth inhibition was observed in survived larvae on inoculated plants vis-a-vis control. Conclusion Establishment of Bt strain as an endophyte in maize plants, complemented with insecticidal activity, could possibly lead to an innovative approach to the management of S. frugiperda and other borers.