Light, temperature, and moisture effects on apothecium production of Sclerotinia sclerotiorum

The purpose of this study was to quantify the effects of light, moisture, a nd temperature on apothecium production of Sclerotinia sclerotiorum. Sclero tia were placed in sand beds in crispers and exposed to two light intensiti es. For each light intensity, sclerotia were subjected to five temperature levels and three moisture levels. The results showed that the optimal tempe rature and temperature range for germination of sclerotia were affected by both light intensity and the moisture level of the sand. At light intensity of 80 to 90 mol m(-2) s(-1) (low light intensity treatment), the optimal t emperatures were in the range of 12 to 18 degreesC regardless of moisture l evel. At light intensity of 120 to 130 mol m(-2) s(-1) (high light intensit y treatment), the optimal temperature was shifted to 20 degreesC when the s oil moisture level was high. Under high light intensity, only a few days we re needed for initials to develop into apothecia. Under low light intensity , several weeks were needed for initials to develop into apothecia. The fre quency with which initials developed into apothecia was high under high lig ht intensity (80%) but low under low light intensity. The initials produced at low light intensity and high temperature (25 to 30 degreesC) were thinn er and longer. The apothecia also were smaller at low light intensity than those produced at high light intensity at any temperature. The periods for apothecium production were longer under lower temperature treatments. The r elationship between apothecium production and degree days was analyzed. Apo thecium production began at about 160 degree days and ceased at about 900 d egree days at high light intensity. However, production began at about 760 degree days and ceased at 1,720 degree days at low light intensity. Nonline ar regression equations which de scribe the relationship between cumulative formation of apothecia and degree days were highly significant. The deviat ion between the observed value and the predicted value increased as degree days increased.