Oral Technical Session: Diseases of Potato

113-O

Pathogenicity and aggressiveness of Alternaria solani, A. alternata, and A. triticina on potato.
L. TYMON (1), T. F. Cummings (1), D. A. Johnson (1)
(1) Washington State University, Pullman, WA, U.S.A.

Alternaria isolates were collected from potato foliage showing symptoms of early blight and brown spot in the Columbia Basin, WA, and Bonners Ferry and Rupert, ID in 2009, 2010, and 2011. Morphological characterization and ITS sequencing identified Alternaria alternata (Aa), A. solani (As) and a novel species identified as A. triticina (At). This is the first documented occurrence of At associated with potato. At has been typically associated with grasses such as durum wheat and barley, which may be grown in rotation with potato in the Columbia Basin. Aggressiveness of At, As and Aa was quantified on unwounded and wounded leaflets of cv Russet Norkotah. Disease incidence, infection frequency (IF), and lesion expansion (LE) of As were significantly greater than Aa or At on both wounded and unwounded leaflets. Wounding of tissue significantly increased infection frequency (IF) and lesion expansion (LE) of Aa and At relative to unwounded tissue. Aa was aggressive on wounded tissue and At was a weak pathogen regardless of wounding suggesting that At is a weak pathogen or saprophyte on potato. Management of Alternaria diseases on potato should continue to be targeted towards As and Aa as At contributes little to overall disease severity in potato fields.