Effects of temperature and leaf wetness on Pyrenophora teres growing on barley cv. Sonja

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Abstract
Conidia ofPyrenophora teresgerminated only in the presence of liquid water and at temperatures above 2°C. The speed with which germination occurred was inversely proportional to temperature measured from a base of 2°C, up to the maximum temperature tested of 21°C. Once conidia on leaves had been wetted, about 40% of all infections that would eventually occur were established within 100°C‐hours. Subsequent lesion extension was rapid, with area doubling times of about 1 day between 10 and 20°C.If conidia germinated, up to 80% formed successful infections on young, susceptible leaves. On older leaves fewer spores germinated and the proportion that then infected was smaller.The latent period, defined as the time before which sporulation did not occur under any wetness conditions, ranged from about 25 days at 5°C to 11 days at 20°C under dry conditions. Under continuously wet conditions it was about 20% shorter at all temperatures. Its inverse had a curvilinear relation to temperature.Spores were produced after one to several days of humidity above 95%. The precise period decreased with increasing temperature, but at 25°C spores never appeared. The drier a dead leaf was, the longer the pathogen in it look to produce spores.