Abstract
In order to examine the effectiveness of use of multiline variety system, simulations of disease increase in the pure stand of susceptible variety and in the mixed stand of susceptible and resistant varieties were made by following the dispersal nature of pathogens.
Dispersal distributions of various pathogens were confirmed to fit the equation y=βe-αd, where y is the number of spores or lesions on a plant, d is distance in meter, and α and β are constant for dispersal gradient and the number of lesions on the source plants, respectively.
When the distance between plants is taken as a unit of distance, if α is less than 0.2 the effect to prevent the disease increase of mixture of resistant plants in susceptible population at a rate of 1:1 can be expressed by the Leonard's equation, y'/y0=mn×(y/y0). The effect of mixing resistant plants decreases in α values over 0.2.
Double or multiple infection and the decrease of healthy area of susceptible plants are presumed to play an important role in flattening of dispersal distribution curve in the actual field as well as contamination from outside sources and the increase of infection generation as pointed out by Cammack.
