Jun 4, 2018
Late blight look-alike spotted in southern US

Jean Ristaino, a professor at North Carolina State University with emphasis in research on Phytophthora infestans, provided University of Wisconsin-Madison Extension a report on a late blight look-alike from tomato and potato in North Carolina.

The southeastern U.S. has been experiencing very high precipitation levels over the past week or so, Ristaino said, and growers are having “big problems with P. nicotianae this season in eastern North Carolina on potatoes.”

Ristaino confirmed the presence of the pathogen by PCR and ITS sequencing – and both pathogen mating types have been identified (the pathogen has an A1/A2 mating type structure like that of the late blight pathogen). The lesions look a lot like late blight with disease on foliage.

University of Wisconsin-Madison warns that leaf spots and stem symptoms caused by Phytophthora nicotianae very closely resemble those produced by the related pathogen Phytophthora infestans, which causes late blight.  These pathogens differ substantially in the quantity of spores (sporangia) they produce, which at least partly accounts for why only late blight is a highly contagious, destructive disease.

P. nicotianae can cause pink rot in tubers. Symptoms have also been reported in other states recently in the region. P. nicotianae on potato is not new, but is rather sporadic in occurrence on potato. The pathogen can cause both foliar and tuber disease on potato. Foliar symptoms look like late blight, but without the signature white pathogen sporulation; tuber symptoms look like pink rot and result in a softer rot, unlike lesions caused by late blight.

More information on this disease can be found in a report by Meg McGrath of Cornell University.



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