Evaluation of entomopathogenic fungus against Alternaria porri (Ellis) causing purple blotch disease of onion

Abstract

Biological control through the use of antagonistic micro-organisms is a potential and non-chemical means of managing plant diseases. Alternaria porri causes purple blotch disease mostly in onion. In this study, three different entomopathogenic fungi, viz. Beauveria bassiana, Metarhizium anisopliae and Verticillium lecanii, were tested against A. porri. All the three entomopathogenic fungi showed inhibitory effect against A. porri subjected to in vitro studies under dual culture technique, spore (conidial) germination, food poisoning (mycelia germination) and seed germination. The percentage inhibition of mycelial growth (PIMG) of A. porri (69.24, 56.17, and 45.81%) and the percentage inhibition of conidial germination (CG) (97.81, 42.11, and 67.69%) were observed for B. bassiana, V. lecanii and M. anisopliae, respectively. Seed germination index was found to be maximum with M. anisopliae (5557 ± 107.7) and B. bassiana (4390 ± 129.9). B. bassiana exhibited efficient antagonism against A. porri showing the highest PIMG and CG with moderate seed germination index. Microscopic examination showed the disintegrated edge of conidia which had turned black and also stopped the growth of germ tube. Hence, these entomopathogenic fungi were found to be more effective antagonistic organisms and also moderately promote seed vigour index (4390 ± 129.9) as well as plant growth. The present study indicated that the entomopathogenic fungi evaluated have shown significant inhibition of A. porri. Thus, there is a possibility of exploiting them in the management of the disease.