PhD

The study entitled “Entomopathogenic fungi for the management of insect pests in rice ecosystem” was carried out during 2011 - 2014 at College of Agriculture, Vellayani. The objectives were to isolate and identify indigenous strains of entomopathogenic fungi, to evaluate the fungal pathogens viz., Beauveria bassiana (Balsamo) Vuillemin, Metarhizium anisopliae Metschnikoff (Sorokin) and indigenous fungi against insect pests of rice, to fix their effective dose, to assess the compatibility of the fungal pathogens with new generation pesticides and to develop pesticide tolerant strains of the fungi.
Six new isolates of entomopathogenic fungi viz., Aspergillus flavus Link. (Af-m1), B. bassiana (Bb-m2, Bb-m3, Bb-m4 and Bb-m5) and one isolate of M. anisopliae (Ma-m1) were collected and identified on the basis of morphological and molecular characters. The accession numbers obtained for the isolates from National Center for Biotechnology Information (NCBI) were KP 739825, KP 739828, KP 739829, KP 739830, KP 739831 and KP 739826, respectively.
The pathogenicity of fungal isolates viz., B. bassiana (Bb 5), M. anisopliae (Ma 4) from NBAIR, B. bassiana (Bb 21) from Department of Microbiology, College of Agriculture, Vellayani and the six new isolates A. flavus (Af-m1), B. bassiana (Bb-m2, Bb-m3, Bb-m4 and Bb-m5) and M. anisopliae (Ma-m1) were evaluated against Cnaphalocrocis medinalis Guen. and Leptocorisa acuta (Thunb). All isolates were pathogenic to larvae of C. medinalis, nymphs and adults of L. acuta. The isolates B. bassiana (Bb 5) and M. anisopliae (Ma 4) were found superior among the fungi evaluated.
The bioassay of the potent fungal pathogens viz., B. bassiana (Bb 5, Bb 21), M. anisopliae (Ma 4) and A. flavus (Af-m1) was conducted against C. medinalis larvae and nymphs and adults of L. acuta and field doses were fixed on the basis of LC90 values. Spore concentration dependent mortality of the insects was seen. The LC90 values were 3.50 x 108, 3.40 x 108, 2.25 x 108 and 3.37 x 108 spores ml-1 for B. bassiana (Bb 5, Bb 21), M. anisopliae (Ma 4) and A. flavus (Af-m1) against C. medinalis larvae, 3.92 x 108, 7.55 x 108, 2.96 x 108 and 3.46 x 108 spores ml-1 against L. acuta nymphs and 4.23 x 1010, 4.11 x 1010, 2.85 x 1010 and 8.72 x 1010 spores ml-1 against L. acuta adults.
Two field trials carried out at Cropping System Research Centre, Karamana during November 2012 to March 2013 (Puncha) and June 2013 to October 2013 (Virippu) to assess
the efficacy of entomopathogens revealed that B. bassiana (Bb 5) @ 1010 spores ml-1 was the best treatment, on the basis of pest population and reduction in damage of pests, population of natural enemies and benefit-cost ratio. This was followed by M. anisopliae (Ma 4) @ 1010 spores ml-1, talc based formulation of Bb 5 @ 20 g l-1, talc based formulation of M. anisopliae (Ma 4) @ 20 g l-1, talc based formulation of Bb 21 @ 20 g l-1 and A. flavus @ 1010 spores ml-1. Among the insecticides evaluated, chlorantraniliprole @ 30 g a.i ha-1 was the best.
Assessment of the compatibility of fungal pathogens with insecticides on the basis of the effect of insecticides on the growth, spore count, germination and bioefficacy revealed that, B. bassiana (Bb5 and Bb 21), M. anisopliae (Ma 4) and A. flavus (Af-m1) were compatible with acephate (0.075, 0.150, 0.225 per cent), chlorantraniliprole (0.004, 0.006 and 0.008 per cent) and thiamethoxam (0.003, 0.005 and 0.008 per cent).
Investigations on pesticide tolerance of entomopathogens showed that, B. bassiana (Bb 5) and M. anisopliae (Ma 4) tolerated 4.0, 8.0 and 8.0 times higher the field dose of acephate, chlorantraniliprole and thiamethoxam, respectively. The growth, spore count and the bioefficacy of selected cultures (fungi gown initially in media containing highest tolerable dose of insecticide and further grown in poisoned media for 10 passages), relaxed cultures (fungi gown initially in media containing highest tolerable dose of insecticide and further grown in unpoisoned media for 10 passages) and untreated cultures (fungi grown only in unpoisoned media) of B. bassiana (Bb 5) / M. anisopliae (Ma 4) differed significantly. On culturing of the selected, relaxed and untreated cultures of the fungi after 10 passages, in still higher dose of the insecticides i.e., 4.5x, 8.5x and 8.5x times higher the field dose of acephate, chlorantraniliprole and thiamethoxam, respectively, only the selected cultures tolerated the higher doses.
Molecular characterisation of the selected, relaxed and untreated cultures of B. bassiana (Bb 5) / M. anisopliae (Ma 4), which were continuously grown for 10 passages in poisoned / unpoisoned media, respectively showed no molecular variations, except a minor polymorphism of 1.61 per cent exhibited in B. bassiana (Bb 5).
To conclude, the six new indigenous fungi isolated are pathogenic to C. medinalis and L. acuta. B. bassiana (Bb 5) and M. anisopliae (Ma 4) @ 1010 spores ml-1 are effective and economical for the management of C. medinalis and L. acuta besides being safe to natural enemies. As these fungi are compatible with acephate @ 750 g a.i ha-1,
chlorantraniliprole @ 30 g a.i ha-1 and thiamethoxam @ 25 g a.i ha-1, and as they tolerated higher doses of insecticides, without undergoing any genetic variation they are suitable for integration with these insecticides, the best chemical suggested for integration is chlorantraniliprole @ 30 g a.i ha-1 as it is safe to natural enemies