Population structure of Alternaria species causing leaf blight of sunflower (Helianthus annuus L.) in India

Leaf blight disease of sunflower caused by Alternaria species is one of the major foliar diseases occurring in sunflower cultivated areas of India. Leaf blight samples collected from sunflower growing areas during rainy season were colonized by Alternariaster helianthi while samples collected during spring season incited by Alternaria alternata. Among two Alternaria species, A. helianthi was the predominant pathogen among the isolates. A total of 220 A. helianthi isolates; 30 A. alternata isolates collected during 2009–10 to 2011–12 from infected sunflower leaves in nine states of India were characterized based on phenotypic, molecular and pathogenic aggressiveness. Molecular identification based on phylogenic analysis using partial internal transcribed spacer regions showed that A. helianthi and A. alternata isolates separated into 11 phylogenetic groups. The pathogenicity on sunflower cultivars KBSH-1, KBSH-44, DRSF-108, PI-535890, TX-16R, Morden revealed that some A. helianthi isolates were highly aggressive with blighting on Morden and DRSF-108. Based on aggressiveness on sunflower cultivars, four groups identified in A. helianthi isolates; three groups in A. alternata isolates. There was no association between phylogenetic group, disease severity and geography of collection among the isolates. Isolates Ah-15, 38, 47, 48, 49, 50, 97, 98, 99, 100, 107, 108, 109, 110, 111, 112, 125 and 126 in A. helianthi; Aa-3, 7, 4 and 9 in A. alternata were aggressive on sunflower cultivars which would be utilized in future disease screening programmes. This is the first report on population structure of Alternaria species and also highlights that A. helianthi is the predominant pathogen associated with sunflower leaf blight in India.