Photoperiod was found to control both initiation of tubers and susceptibility of potato toVerticilliumwilt. Plants grown in a short-daily photoperiod (long dark period) formed tubers and such plants, when inoculated withVerticillium albo-atrum, developed moderate to severe wilt symptoms. Plants grown in a long-daily photoperiod did not form tubers and developed no disease symptoms when inoculated withVerticillium. When a 2-hour light period was interjected in the middle of the long dark period, no tubers were formed and plants developed no symptoms of disease when inoculated withVerticillium. The resistance toVerticilliumexhibited by plants was not limited to the root but was present throughout the plant.
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