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APSEducationDisease Impacts & ManagementTopicsCultivar MixturesUltimate lesion size

Crops and diseases suited to cultivar mixtures
Ultimate Lesion Size

Continuous expansion of individual lesions, in the cases that it is possible, decreases the degree of disease suppression achieved by mixing host genotypes because it increases the rate of new infection of the susceptible genotype (Garrett and Mundt 1999). Thus, analogous to genotype unit area, cultivar mixtures for disease suppression are most effective when the size of individual lesions remains small. Non-expanding lesions require a proportionally greater number of infections for the disease epidemic to progress. The dilution and barrier effects influence the number of new infections but not the rate of lesion expansion. Leaf rust of wheat (Puccinia recondita) is an example of a disease with a small determinant lesion size. Stripe rust of wheat (Puccinia striiformis) shows substantial lesion expansion and, thus, cultivar mixtures may be expected to have somewhat less impact on suppression of this disease (Lannou et al. 1994).
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