Morphological, Pathogenic and Molecular Characterizations of Alternaria Species Causing Early Blight of Tomato in Northern India

Abstract

Early blight disease samples were collected from six different states of India. Seventeen different isolates of Alternaria spp were obtained in pure culture which were designated as PB-2, PB-4, PB-13, PB-17, PB-19, HR-12, HR-44, HR-62, MP-6, MP-7, JT-4, JT-11, UP-7, UP-10, UP-15, UP-20 and RJ-T-1. Characterization based on culture colour and conidial dimensions (conidial length and breadth, and beak length) indicated that no distinguished variation of the isolates was observed on the colour parameters. Although, a wide variation was observed in the length of conidia and beak, no significant difference was observed in conidial breadth except RJ-T-1. Among the isolates, conidial length of five isolates viz., HR-12, UP-7, UP-10, UP-15 and RJ-T-1 ranged from 80 to 97 µm whereas others were of significantly lesser size (30–51 µm). Similarly, significant difference was observed in beak length. The PCR amplification of the fungal DNA using universal primers ITS1 and ITS4 and sequencing indicated that, out of 17 isolates, 12 (JT-4, JT-11, HR-62, HR-44, PB-2, PB-4, PB-13, PB-17, PB-19, UP-20, MP-6 and MP-7) were closely matching with A. alternata (JX993756) and five isolates (HR-12, UP-7, UP-10, UP-15 and RJ-T-1) with A. solani (JF796068). Further, pathogenicity test on tomato revealed that both A. alternata and A. solani isolates were of virulent category indicating that former is also an incitant of early blight in northern India.