Morphological, Biochemical and Genetic Characterisation of Entomopathogenic Bacteria infesting Maize Fall Armyworm, SpodopterafrugiperdaJ.E Smith (Noctuidae; Lepidoptera) Collected from Different Parts of Tamil Nadu

Abstract

Abstract Regular field surveyswere conducted at major maize growing tract of Tamil Nadu viz., Perambalur, Tiruchirappalli, Dindigul and Madurai during 2019-2022for exploring the naturally occurring entomopathogensin maize fall armyworm (FAW), Spodopterafrugiperda. The pathogens collected were isolated, identified, characterised, sequenced and the efficacywas studiedagainst fall armyworm at the Department of Plant Protection, AnbilDharmalingam Agricultural College and Research Institute, Tiruchirappalli. Results showed that15 isolates yielded from the 24 bacterial diseased cadavers were screened for the presence of Bacillus thuringiensis. Outof 345 colonies, 205 colonies were morphologically similar to Bacillus and 66 colonies produced crystal proteins. Distribution frequency of B. thuringiensis in cadavers of S. frugiperdaranged from0.17 to 0.43 per cent. Occurrence of B. thuringiensis was highest in isolate TRY 1 (0.43 %) followed by isolate TRY 6 (0.40 %) and lowest frequency was observed in isolates TRY 3 and TRY 14 (0.17 %). The mean B.t index was 0.32 per cent.Colour, shape, margin, elevation and texture of the B.t colonies varied. Colonies of all the isolates were creamy white / milky white / yellowish white in colour with regular / irregular shape, entire / serrate / undulated margin, raised / flat elevation and smooth / rough in texture. All the 15 isolates produced were rod shaped, violet coloured cells which specified the presence of grampositiveBacillussp.Biochemical characterization was done for 15 isolates and one reference strain (HD 1). Isolates TRY 2, TRY 5, TRY 7, TRY 12 and TRY 13 were non-motile while the other isolates were motile. Isolates such as TRY 2, TRY 5, TRY 10 and TRY 15 showed negative result to methyl red (MR) test whereas the other isolates showed positive results. For VogesProskauer (VP) test, except isolate such as TRY 2, TRY 5, TRY 7, TRY 10, TRY 13 and TRY 15 showed positive results, while remaining isolates showed negative results for VP test. For catalase test, TRY 2, TRY 4, TRY 7, TRY 10 and TRY 12 isolates showed negative, while the other isolates showed positive results. Isolates viz., TRY 4, TRY 9, TRY 13 and TRY 15 showed negative result for starch hydrolysis test, whereas the other isolates showed positive results.The results of the protein profile analysis using SDS PAGE from B.t isolates revealed thatTRY 1, TRY 3, TRY 6, TRY 8, TRY 11, TRY 14 isolates showed major protein bandaround 60-75kDa and the standard strain HD-1 showed protein band around 130 kDa. Molecular characterization and identification of Bacillus sp. using 16S rRNA gene sequence and NCBI – BLAST analysis clearly revealed that all the isolates showed high similarity with Bacillus thrungiensis.Pathogenicity of the B.t isolates against the second instar of S. frugiperdadiffered in their toxicity and the mortality ranged from 20.00 to 47.5 per cent. Isolate TRY 3 showed maximum mortality of 47.5 per cent followed by TRY 6 which produced 45 per cent and the lowest mortality was obtained in isolate TRY 1 isolate (20 %).