Abstract
Eleven rice varieties with and without a resistance gene, Pi-z, were tested for their blast resistance in two blast nurseries in Takayama, Gifu Prefecture and Inabu, Aichi Prefecture. Disease severity was measured mainly by the number of lesions per plant and the proportion of diseased leaf-area in Takayama and Inabu, respectively. In both cases, field susceptibility was evaluated by estimating the infection rate on each variety. Infection rate was calculated by various methods. A significant varietal difference of infection rates was obtained in an experiment with three or four replications. The highest correlation coefficient between infecton rates of two nursery tests and that between those of the nursery tests and the field test in the previous paper were obtained when the infection rate was calculated using the equation, rx=(lnX2/1-x2-lnx1/1-x1)/(t2-t1). A low correlation coefficient was obtained between infection rates measured at different periods, indicating the importance of choice of dates for rating.
