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.
<i>Alternaria</i> 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 <i>Alternaria alternata</i> (<i>Aa</i>), <i>A. solani</i> (<i>As</i>) and a novel species identified as <i>A. triticina</i> (<i>At</i>). This is the first documented occurrence of <i>At</i> associated with potato. <i>At</i> 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 <i>At</i>, <i>As</i> and <i>Aa</i> was quantified on unwounded and wounded leaflets of cv Russet Norkotah. Disease incidence, infection frequency (IF), and lesion expansion (LE) of <i>As</i> were significantly greater than <i>Aa</i> or <i>At</i> on both wounded and unwounded leaflets. Wounding of tissue significantly increased infection frequency (IF) and lesion expansion (LE) of <i>Aa</i> and <i>At</i> relative to unwounded tissue. <i>Aa</i> was aggressive on wounded tissue and <i>At</i> was a weak pathogen regardless of wounding suggesting that <i>At</i> is a weak pathogen or saprophyte on potato. Management of <i>Alternaria</i> diseases on potato should continue to be targeted towards <i>As</i> and <i>Aa</i> as <i>At</i> contributes little to overall disease severity in potato fields.
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