Ascospore discharge by Fusarium graminearum as affected by temperature and relative humidity

Fusarium graminearum is the most important species causing Fusarium head blight of small-grain cereals. Ascospore discharge from F. graminearum perithecia was studied under controlled conditions, i.e., between 5 and 40 °C in a saturated atmosphere and between 44.5 and 100 % relative humidity at 20 °C. Ascospores were collected on microscope slides placed directly below maize stalk plugs bearing mature perithecia, and were enumerated daily for 5 days. Discharge was detected at all temperatures and relative humidities on the first day; no discharge was detected for temperatures >30 °C or relative humidities ≤76 % after the first day. Ascospore discharge was highest between 15 and 25 °C (optimum at 21 °C) and at 100 % relative humidity. Some ascospores were discharged at any of the tested temperatures and relative humidities. A Bete equation described ascospore discharge as a function of temperature (R2 = 0.99), and an exponential equation described ascospore discharge as a function of relative humidity (R2 = 0.97).