Abstract
Rusts are important pathogens of angiosperms and gymnosperms including cereal crops and forest trees. With respect to cereals, rust fungi are among the most important pathogens. Cereal rusts are heteroecious and macrocyclic requiring two taxonomically unrelated hosts to complete a five spore stage life cycle. Cereal rust fungi are highly variable for virulence and molecular polymorphism. Leaf rust, caused by Puccinia triticina is the most common rust of wheat on a worldwide basis. Many different races of P. triticina that vary for virulence to leaf rust resistance genes in wheat differential lines are found annually in the US. Molecular markers have been used to characterize rust populations in the US and worldwide. Highly virulent races of P. triticina are selected by leaf rust resistance genes in the soft red winter wheat, hard red winter wheat and hard red spring wheat cultivars that are grown in different regions of the US. Cultivars that only have race-specific leaf rust resistance genes that are effective in seedling plants lose their effective resistance and become susceptible within a few years of release. Cultivars with combinations of race non-specific resistance genes have remained resistant over a period of years even though races of the leaf rust population have changed constantly.
Highlights
The rust fungi are among the most widely spread of plant pathogens and cause important diseases on many angiosperm and gymnosperm trees, and cereal and legume crops to name just a few major plant classes afflicted by rusts [1]
Many winter wheat cultivars are susceptible to leaf rust, this allows a large population of P. triticina to overwinter over a large geographic region on an annual basis
The soft red winter wheat cultivars in these states commonly have leaf rust resistance genes Lr9, Lr11, Lr18 or Lr26, which have selected for races with virulence to these genes
Summary
The rust fungi are among the most widely spread of plant pathogens and cause important diseases on many angiosperm and gymnosperm trees, and cereal and legume crops to name just a few major plant classes afflicted by rusts [1]. Rust fungi are obligate parasites that require a living host to Forests 2013, 4 complete the life cycle, and biotrophs due to their method of extracting nutrients from living host cells [2]. Due to these characteristics of parasitism, most rust fungi are highly specialized pathogens specific to certain host species. The same issues of pathogen genetic variation, pathogen dissemination and how the rust pathogens interact with host genotypes to cause disease are critical aspects of rust diseases of both perennial species such as trees and annual field crops.
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