Endophytic association of entomopathogenic fungi with rice and cowpea

Abstract

The study entitled ‘Endophytic association of entomopathogenic fungi with rice and cowpea’ was carried out in the Department of Agricultural Entomology, College of Agriculture, Vellayani, Thiruvananthapuram, during the year 2017-19, with the objective to examine the endophytic association of entomopathogenic fungi in rice and cowpea. The entomopathogenic fungi, evaluated were Beauveria bassiana, Metarhizium anisopliae, Lecanicillium lecanii and Lecanicillium saksenae. They were tested through seven inoculation methods viz., seed coating, seed soaking, radicle dressing, root dipping, soil drenching, foliar spraying and bloom spraying by inoculating the conidial suspension at their effective doses. Among the four entomopathogenic fungi inoculated, B. bassiana, M. anisopliae and L. saksenae were found to colonise rice plants. B. bassiana was found to colonise in stem and roots, while M. anisopliae preferred stem. Both B. bassiana and M. anisopliae colonized effectively by seed soaking method. L. saksenae colonised in the stem and roots in seed soaking, in the roots in soil drenching and in the leaves in foliar spraying method. In plants, B. bassiana and M. anisopliae persisted up to 15th day after inoculation (DAI), while L. saksenae persisted till 45th DAI. In soil, L. saksenae persisted in soil up to 45th day, while other fungi could not be retrieved from soil. L. lecanii could not be retrieved from any of the plant parts or soil up to 45th DAI. Thirteen natural endophytes were isolated from rice, which included growth promoters with nitrogen fixing properties, gibberellic acid production properties, saprophytes and plant pathogens. They were identified with the help of colony and conidial characters. Those fungal endophytes whose identity could not be confirmed were characterised at molecular level through ITS sequencing, and bacterial endophytes through 16S sequencing. The most dominant endophyte in rice was the fungus, Neocomospora rubicola, a known plant pathogen followed by the nitrogen fixing bacterium Burkholderia cepacia. Colonisation of fungal bacterial association Sarocladium oryzae + Kosakonia sacchari was also dominant in the stem. S. oryzae is a known plant pathogen while K. Sacchari is a nitrogen fixing bacterium. The other endophytes with less frequency of occurrence were Pestalotiopsis microspora, Cladosporium sp., Microdochium fisheri, Fusarium solani, Aspergillus and Penicillium. Experiments in cowpea revealed that all the four fungi could successfully colonize different plant parts. Foliar spraying was the best method in cowpea to get endophytic association of all the four fungi, while M. anisopliae could also be retrieved through seed soaking and root dipping methods. B. bassiana, M. anisopliae and L. saksenae were found to colonise leaves, stem and roots, while L. lecanii colonised only on leaves. In cowpea plants, M. anisopliae and L. saksenae were found to be more persistent (up to 45th DAI), while B. bassiana and L. lecanii persisted only up to 30 DAI. Soil samples revealed the presence of B. bassiana, M. anisopliae and L. saksenae up to 15th, 30th and 45th DAI respectively. L. lecanii was not found to colonise soil. Grain samples in rice and bloom samples in cowpea did not reveal the presence of any endophytes. In cowpea, several natural endophytes were found to be stumped upon in different parts, which included four fungi and two bacteria. Apart from this a fungal bacterial association, Fusarium + Ebc 3 (unidentified bacterium) was found to be a dominant endophyte. The bacterium Rhizobium mayense isolated from all plant parts was the most dominant endophyte. The other endophytes isolated were the fungi, Cladosporium sp., Clonostachys rosea, Chaetomium globosum and Cerrena sp. and the bacterium Enterobacter cloacae. Rice plants inoculated by seed soaking, with the conidial suspensions of B. bassiana and M. anisopliae @ 108 spores ml-1 and L. saksenae @ 108 spores mL-1 reflected 28.79, 27.17 and 29.99 per cent increase height, 47.71, 44.75 and 47.92 per cent increase in biomass and 37.73, 36.97 and 39.89 per cent increase in grain yield, the highest values being those of L. saksenae and lowest being those of M. anisopliae. Incidence of rice bug assessed in terms of percentage of chaffy grains per panicle was significantly less in L. saksenae (14.21), while in B. bassiana it was 20.48 and in M. anisopliae, 21.61. There was no disease incidence in treated as well as control plants. It is concluded that B. bassiana, M. anisopliae and L. saksenae has endophytic association with rice and cowpea and L. saksenae is a strong endophyte.