Biological control of early blight disease of potato caused by Alternaria alternata EBP3 by an endophytic bacterial strain Bacillus velezensis SEB1

Abstract

Early blight is a well known disease causing severe loss in potato production which is used as staple food in many parts of the world. For overcoming the drawbacks of chemical fungicides used for controlling the disease, searching of suitable biocontrol agents are essential. In the present endeavour, the fungal pathogen was isolated and identified from the infected leaves of potato grown in the lateritic belt of Santiniketan, West Bengal, India. Based on morphological characteristics and sequencing of ITS region, the isolated pathogen EBP3 was identified as Alternaria alternata instead of Alternaria. solani. The pathogen was further confirmed by pathogenecity test following pot based experiment. One endophytic bacterial strain Bacillus velezensis SEB1 isolated from Vigna mungo (L.) Hepper was checked for its biocontrol efficacy against the isolated pathogen. SEB1 was found effective for inhibiting the pathogenic growth on dual culture overlay plates. In addition to fungal cell wall degrading enzymes ß-glucanase and protease, SEB1 can secrete thermostable antifungal metabolites to the extracellular broth which are insensitive to proteinase K. The crude EA fraction of the CFS of SEB1 inhibited the conidial germination and germ tube elongation of EBP3. 82.34 ± 4.56% inhibition in fungal radial growth was also observed in the presence of EA fraction at 1000 µg/ml. In vivo challenge experiments suggested decrease of disease severity form 52.47 ± 3.8% to 9.59 ± 2.1% due to application of the biocontrol agent SEB1. Based on overall observation the endophytic bacterial isolate SEB1 can be considered as a suitable biocontrol agent for controlling the early blight of potato caused by A. alternata.