  A looming challenge for agriculture is sustainable intensification of food
production to feed the growing human population. Current chemical and genetic
technologies used to manage plant diseases are highly vulnerable to pathogen
evolution and are not sustainable. Pathogen evolution is facilitated by the
genetic uniformity underlying modern agroecosystems, suggesting that one path
to sustainable disease control lies through increasing genetic diversity at the
field scale by using genetically diverse host mixtures. We investigate how host
mixtures can improve disease control using a population dynamics model. We find
that when a population of crop plants is exposed to host-specialized pathogen
species or strains, the overall disease severity is smaller in the mixture of
two host varieties than in each of the corresponding pure stands. The disease
severity can be minimized over a range of mixing ratios. These findings may
help in designing host mixtures that efficiently control diseases of crops. We
then generalize the model to describe host mixtures with many components. We
find that when pathogens exhibit host specialization, the overall disease
severity decreases with the number of components in the mixture. As the degree
of specialization increases, the decrease in disease severity becomes larger.
Using these model outcomes, we propose ways to optimize the use of host
mixtures to decrease disease in agroecosystems.
