Relating germination dynamics of Melampsora pinitorqua teliospores to temperature and rainfall during overwintering

The influence of overwintering conditions on the dynamics of Melampsora pinitorqua teliospore germination in spring was assessed in the Landes forest (south-western France), over 3 years. January accumulated temperature was the variable most strongly linked to the date of optimum germinability (JDOG), in a negative direction. A linear regression using accumulated degree-days and number of rainy days in January accounted for nearly 70% of overall variation in JDOG. Accumulated temperature from October 1 and January 1 to the date of optimum germinability showed lower coefficients of variation than JDOG. The best predictions of JDOG in an independent data set were obtained by using the accumulated temperature from January 1 to the dare of optimum germinability or a linear regression based on accumulated temperature in January. The mean square root error of prediction was approximately 5 days. The ecological significance of the temperature-dependent model is discussed in relation to the synchronization of rust and pine phenologies.