The Efficacy of Mixtures of Susceptible and Resistant Hosts to Two Wheat Rusts of Different Lesion Size: Controlled Condition Experiments and Computerized Simulations

Controlled‐environment experiments and computerized simulations on wheat yellow rust and wheat brown rust epidemics indicated that mixtures of resistant and susceptible hosts controlled parasites with small lesions more effectively than parasites with large lesions. Experiments were conducted on seedlings, during two parasitic cycles. Yellow rust lesions were about 200 times larger than those of brown rust. The measured efficacy of seedling mixtures in reducing disease spread was 22 % for yellow rust and 46 % for brown rust. Computerized simulations suggested that, for a given quantity of inoculum, mixture efficacy was limited for a large‐lesion parasite because of fast host‐plant saturation.