The Effect of Freezing Temperatures onMicrodochium majusandM. nivaleSeedling Blight of Winter Wheat

Abstract

Exposure to pre-emergent freezing temperatures significantly delayed the rate of seedling emergence (P<0.05) from an infected and a non-infected winter wheat cv. Equinox seed lot, but significant effects for timing of freezing and duration of freezing on final emergence were only seen for theMicrodochium-infested seed lot. Freezing temperatures of−5∘C at post-emergence caused most disease on emerged seedlings. Duration of freezing (12 hours or 24 hours) had little effect on disease index but exposure to pre-emergent freezing for 24 hours significantly delayed rate of seedling emergence and reduced final emergence from the infected seed lot. In plate experiments, the calculated base temperature for growth ofM. nivaleandM. majuswas−6.3∘C and−2.2∘C, respectively. These are the first set of experiments to demonstrate the effects of pre-emergent and post-emergent freezing on the severity ofMicrodochiumseedling blight.