Variety mixtures and the blighted organic potato

There is a need to better understand the usefulness of variety mixtures for the prevention of late blight in organic potatoes. It is only in certain variety combinations that mixture responses, in terms of disease and/or yield, are important. This, coupled to evidence from different plot sizes, indicates that the usual mixture mechanisms of barrier effects, the spatial separation of susceptibles and induced resistance, are not always important in potato variety mixtures. It is proposed that plant-plant interactions may also have an important role.