COLLETOTRICHUM SIAMENSE AND C TRUNCATUM ARE RESPONSIBLE FOR SEVERE OUTBREAKS OF ANTHRACNOSE ON ONION IN SOUTHWEST INDIA
P. Chowdappa, C.S. Chethana, K.V. Pavani
Colletotrichum species responsible for severe outbreaks of anthracnose on onion in southwest India are reported. These fungi produced white, oval sunken lesions on the leaves and neck at the onset of infection followed by appearance of necrotic centres with grey-colored concentric rings of acervuli, which eventually covered the whole leaves and subsequently led to collapse of the plant. Thirty seven isolates of Colletotrichum recovered from diseased leaves and neck were characterized based on morphological characteristics and partial sequences of ACT, TUB2, CHS-1, CAL, CYLH3, GAPDH, GS and ITS genes. The combined multilocus sequence analysis coupled with a critical examination of the phenotypic characters revealed the presence of two species, Colletotrichum siamense (27 isolates) and Colletotrichum truncatum (10 isolates). Pathogenicity of both species was ascertained on onion seedlings of cv. Arka kalyan. To our knowledge, this is the first report of C. siamense and C. truncatum causing anthracnose disease on onion.