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<div>Wheat blast is an emerging disease in South America and Asia caused by the Triticum pathotype<i> </i>of <i>Magnaporthe oryzae</i> (MoT). Although MoT has not yet been reported in North America, the closely related <i>M. oryzae</i> Lolium pathotype (MoL) is commonly found in wheat growing regions and could pose a threat under certain environmental conditions. Multifactorial experiments were conducted under controlled conditions to evaluate the effects of different combinations of temperature (20, 25, and 30 C), 100% relative humidity (RH) duration (0, 3, 6, 12, 24, and 48 h), inoculum concentration (2e2, 2e3, 2e4, and 2e5 spores/ml), and growth stage (Feekes 10.1-3, 10.5, 10.5.1, and 10.5.4) on MoL infection and blast development. MoL infected and blast developed under all conditions evaluated, but results from linear mixed model regression analyses showed that response to inoculum density was significantly greater (<i>P</i>< 0.05) when infections occurred at Feekes 10.5.1 (anthesis) or 10.5.4 than between Feekes 10.1 and 10.5. When infected at anthesis, there was a significant positive linear relationship between arcsine square root blast severity (arcSEV) and high RH duration, but slopes for this relationship varied among temperatures. The rate of increase in arcSEV per hour increase in 100% RH was significantly greater at 25 and 30C than at 20C. Similar trends were observed for blast incidence. These results are invaluable for ongoing efforts to assess the risk posted by MoL to US wheat.</div>