Effects of temperature on the latent period of the rose powdery mildew pathogen, Sphaerotheca pannosa

The effects of temperature on the length of the latent period of rose powdery mildew, caused by Sphaerotheca pannosa var . rosae , were studied. At constant temperatures over the range of 10–28°C, the length of the latent period ranged from 4 to 10 days. The relationship between temperature and the rate of fungal development during the latent period (expressed as the reciprocal of the latent period) was described by a nonlinear (thermodynamic) model. The resulting curve was asymmetrically bell-shaped with an optimum temperature of about 22°C. The latent period was further subdivided into two periods: incubation period (from inoculation to visible colonies) and postincubation period (from visible colonies to the first sign of conidiophores). The relationship between temperature and the rate of fungal development during the incubation period (expressed as the reciprocal of the incubation period) was also well described by a thermodynamic model. In contrast, the relationship between temperature and the rate of fungal development during the postincubation period (expressed as the reciprocal of the postincubation period) was approximately linear. The latent period under fluctuating temperatures was predicted using a two-stage integration scheme at a step of 24 min by first integrating the incubation rate and then the postincubation rate. The predicted length of the latent period agreed well with the observed values.