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Investigating Alternaria species composition and role in the potato early blight complex in Wisconsin
S. DING (1), K. Meinholz (1), A. J. Gevens (1). (1) UW-Madison, Madison, WI, U.S.A.

The potato early blight complex (EBC), caused by <i>Alternaria solani</i> and <i>A. alternata</i>, is a perennial and destructive potato disease. Infected leaves develop necrotic lesions which can cause loss in tuber quality and quantity. Currently no commercial cultivars are resistant to the EBC, so control is maintained through fungicide application. An improved understanding of the ecology and epidemiology of the EBC pathogens would enhance fungicide program design and overall EBC management. Our initial study focused on the pathogen population assemblage in the field in 2014. Results indicated an earlier emergence of <i>A. alternata</i> and a possible interaction between the pathogens. There was an inverse relationship between disease severity and quantity of <i>A. alternata</i> present at sampled field sites. A greenhouse experiment with conidial inoculations of the two pathogens revealed that <i>A. solani</i> was the major pathogen causing symptoms on potato plants. Greater disease was observed when <i>A. alternata</i> and <i>A. solani</i> were inoculated simultaneously, and less disease was observed when <i>A. alternata </i>was inoculated two days prior <i>A. solani</i>. Because <i>A. alternata</i> is a weak pathogen, it causes less severe disease symptoms but may trigger plant defenses thereby limiting severity of subsequent <i>A. solani</i> infection. Further studies will be conducted to better understand role of <i>A. alternata</i> in EBC and the interactions between the two pathogens. 

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