Informatics Publishing Limited

V. Velavan ¹, G. Sivakumar ¹, R. Rangeshwaran ¹, R. Sundararaj ², T. O. Sasidharan ³

Affiliations
1 ICAR-National Bureau of Agricultural Insects Resources, Bangalore – 560024, Karnataka, IN
2 Institute of Wood Science and Technology, Bangalore – 560 003, Karnataka, IN
3 Ashoka Trust for Research in Ecology and the Environment (ATREE), Bangalore – 560064, Karnataka, IN

Abstract

Studies were conducted to systematically isolate Metarhizium isolates from the insect cadavers and soils of South India. Morphological and PCR amplified sequences of 5.8S ITS regions and RNA polymerase II largest subunit (RPB1) gene regions were used to identify the isolates at species level. Eight Metarhizium isolates were isolated and initially identified by morphological and microscopic studies. Further identification was confirmed through 5.8SrRNA ITS and RPB1 analysis. They were identified as three isolates of M. robertsii J.F. Bisch., Rehner & Humber sp. nov. (ArMz3R, ArMz3S and ArMz6W), one isolate of M. majus (J.R. Johnst.) J.F. Bisch., Rehner & Humber (VjMz1W) and four isolates of M. anisopliae (WnMz1S, NlMz2S, BgMz2S and DhMz4R). Topical conidial suspensions (TCS) and powder based formulations (PBF) of the eight indigenous isolates of Metarhizium spp. that were isolated from insect cadavers and soils of South India were tested against coleopteran pests Holotricha serrata L. and Oryctes rhinoceros L. that cause serious damage to sugarcane and palm trees respectively. Against H. serrata TCS of M. robertsii (ArMz6W) was the most effective with an LC₅₀ of 6.893×10⁵ cfu/ml and caused 100% mortality against the 3^rd instar larvae in 5 days; PBF elicited an LC₅₀ of 7.502×10⁵ cfu/ml with 96% mortality in 10 days. Against O. rhinoceros TCS (LC₅₀ of 9.75×10⁵ cfu/ml) of M. majus (VjMz1W) caused 90% mortality in 7 days and the PBF (LC₅₀ of 9.57×10⁵ cfu/ml) caused 86% mortality in 14 days. The results establish that M. robertsii is highly effective against H. serrata and against O. rhinoceros, M. majus was the most effective. The TCS formulations of these two strains can be readily deployed for field applications.

Keywords

Holotricha serrata, Metarhizium spp., Oryctes rhinoceros, Powder Based Formulation (PBF), Topical Conidial Suspension (TCS).

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R. Rangeshwaran ¹, V. Velavan ², Satendra Kumar ², V. Apoorva ², K. M. Venugopala ², A. N. Shylesha ², G. Sivakumar ²

Affiliations
1 ICAR-National Bureau of Agricultural Insect Resources, H.A. Farm Post, Hebbal, Bellary Road, Bengaluru – 560024, Karnataka, IN
2 ICAR-National Research Centre for Banana, Thogaimalai Rd, Podavur, Thiruchirapalli – 620102, Tamil Nadu, IN

Abstract

The search for new Bacillus thuringiensis (Bt) strains is a continuous process and researchers are now focusing on finding toxin proteins that are toxic to pests of insect orders that are not reported. In the present study soil and insect cadaver samples were collected from North East India comprising the states of Assam, Tripura and Mehhalaya and native Bt were isolated using standard protocols. At total of 30 Bt isolates were purified and characterized. Various types of crystal morphology were encountered that included bipyramidal, cuboidal, square, rhomboid, spherical and irregular. PCR analysis showed that diverse cry genes were expressed. The cry genes identified were Lepidoptera, Coleoptera and Diptera specific. Detected genes included cry1Ac, cry2A, cry4A, cry10A, cry16A, cry17A, cry19A, cry30Aa, cry44Aa, cry11A, cry4B, cry12A, cry8A and cry7A. Many of them were positive for Vip3A protein. The coleopteran specific Bt were evaluated against Sitophilus oryzae and Callosobruchus chinensis and NBAIR-AgBt6 was found to be toxic. The isolates are being further evaluated for use as biopesticides.

Keywords

Bacillus thuringiensis, Bioassay, Cry Genes, Diversity, North East.

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