Temperature dependent seed transmission of Stagonospora nodorum in wheat

The transmission of Stagonospora nodorum from four naturally infected winte r wheat seedlots was quantified in controlled environment germination chamb ers at 9, 13, 17, 21, and 25 degreesC. Seedlings were harvested when the se cond leaf began to emerge. Coleoptiles and first seedling leaves were exami ned for the presence of lesions caused by S. nodorum. First leaves were inc ubated on Bannon's medium for 2 weeks, after which they were examined for p ycnidia of S. nodorum. Transmission to the coleoptile occurred at all tempe ratures, but decreased from 100% to 72% as temperature increased from 9 to 25 degreesC. Transmission to the first leaf was less, dropping from 37% to 2% as temperature increased from 9 to 25 degreesC. At least 44% of infected first leaves were symptomless at all temperatures, with 96% of infected le aves showing no symptoms at 25 degreesC. Transmission to seedling leaves oc curred over a broad temperature range. Under the high densities at which wh eat is sown, a significant number of infected seedlings per unit area may o riginate from relatively low initial seed infection levels and transmission efficiencies.