Landscape-scale disease risk quantification and prediction

The study of plant disease epidemics at a landscape scale can be extended to allow for predictions about disease occurrence at this scale. Examined within the context of the disease triangle, systems developed to incorporate information primarily about the pathogen and conditions conducive to the infection process. Parametric methods can be used to relate environmental conditions to disease, and specifically relate environment to the inoculum production, the resulting infection process, or both. Aspects relating to the presence or absence of the host plant within the landscape, or patterns of the host within the landscape, are much rarer in disease prediction, although analyses incorporating these factors have been conducted. Predictive systems at the landscape scale may concentrate only on the conditions for infection or possible migratory paths of pathogen propagules. Incorporation of all components of the disease triangle may be one way to improve these systems.

Diversity of Puccinia striiformis on cereals and grasses

Yellow (stripe) rust is a common fungal disease on cereals and grasses. It is caused by Puccinia striiformis sensu lato, which is biotrophic and heteroecious. The pathogen is specialized on the primary host at both species and cultivar levels, whereas several Berberis spp. may serve as alternate hosts. One lineage infects mainly cereals and at least two lineages are restricted to grasses. P. striiformis on cereals has a typical clonal population structure in many areas, resulting from asexual reproduction, but high diversity, suggesting frequent recombination, has been observed in certain areas in Asia. Yellow rust is spreading by airborne spores potentially across long distances, which may contribute to sudden disease epidemics in new areas. This has been the case since 2000, where large-scale epidemics in warmer wheat-growing areas have been ascribed to the emergence of two closely related yellow rust strains with increased aggressiveness and tolerance to warm temperatures.