Diversity analysis of Alternaria porri (Ellis) Cif -causal organism of purple leaf blotch of onion Chowdappa P.*, Sandhya H., Bhargavi B. Reddi Indian Institute of Horticultural Research, Hessaraghatta Lake Post, Bangalore – 560 089 *Corresponding author - pallem22@gmail.com
Online published on 4 December, 2019. Abstract Purple leaf blotch (PLB), caused by Alternaria porri (Ellis) Cif, is the most destructive disease of onion in India. Phenotypic and genetic diversity of 19 A. porri isolates collected from different farms in Karnataka state of India was characterized based on morphology, aggressiveness, response to the fungicides (chlorothalonil and mancozeb), and genetic analysis using sequencing of ITS region of rDNA. All A. porri isolates produced typical orange color pigmentation on potato dextrose agar (PDA). Isolates exhibited significant differences in their aggressiveness on onion variety, Arka kalyan and could be categorized into highly aggressive, moderately aggressive and less aggressive groups. Comparative fungicidal assays indicated that isolates were more sensitive to chlorothalonil than to mancozeb. EC50 values for inhibition of mycelia growth ranged from 3.07 to 48.30 μg/ml for chlorothalonil and 33.22 to 76.90 μg/ml for mancozeb. Isolates could be separated into two groups based on phylogenetic analysis of ITS sequences; Clade I contains highly and moderately aggressive isolates and clade II contains less aggressive and nonpathogenic isolates. Thus, the present study demonstrated existence of phenotypic and genotypic diversity among A. porri isolates collected from areas of commercial onion production, which has implications in breeding onion for resistance to purple blotch. Top Keywords Onion, purple leaf blotch, Alternaria porri, onion, genotypic diversity. Top |