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 powde ry mildew, caused by Sphaerotheca pannosa var, rosae, were studied. At cons tant temperatures over the range of 10-28 degrees C, the length of the late nt period ranged from 4 to 10 days. The relationship between temperature an d the rate of fungal development during the latent period (expressed as the reciprocal of the latent period) was described by a nonlinear (thermodynam ic) model. The resulting curve was asymmetrically bell-shaped with an optim um temperature of about 22 degrees C. The latent period was further subdivi ded into two periods: incubation period (from inoculation to visible coloni es) and postincubation period (from visible colonies to the first sign of c onidiophores). The relationship between temperature and the rate of fungal development during the incubation period (expressed as the reciprocal of th e incubation period) was also well described by a thermodynamic model, In c ontrast, the relationship between temperature and the rate of fungal develo pment during the postincubation period (expressed as the reciprocal of the postincubation period) was approximately linear. The latent period under fl uctuating temperatures was predicted using a two-stage integration scheme a t a step of 24 min by first integrating the incubation rate and then the po stincubation rate. The predicted length of the latent period agreed well wi th the observed values.