INFLUENCE OF TEMPERATURE AND MOISTURE ON GROWTH, SPORE PRODUCTION, AND CONIDIAL GERMINATION OF MONILINIA-LAXA

The effect of temperature on mycelial growth and spore production of Monilinia laxa, the brown rot fungus of sweet cherry, was studied in vitro as well as the effect of temperature, moisture, and relative humidity on conidial germination. Mycelial growth was observed at 2.5-30 C. A model was fitted to the data, and the optimum was calculated as 24.8 C. A comparison in a second experiment between observed and predicted growth indicated that diurnal cycles of temperature (3/12 or 10/22 C) did not alter the growth rates compared to growth at constant temperatures. M. laxa produced the highest daily number of conidia at 10 C, with 29.4 X 10(6) conidia per colony within 15 days. The maximum germination fraction of conidia reached 98% when suspended in deionized water and exposed to 15-25 C. Germination was evident after 2 to 4 h. M. laxa was able to germinate in the absence of free moisture at relative humidities from 97 to 100%. A mechanistic model was evaluated to predict the germination process as a function of time and temperature. The model yielded close fits to the observed data.