Abstract
Race-specific or vertical resistance implies resistance to some pathogen isolates and not to others and is relatively simply inherited. Nonspecific or horizontal resistance implies resistance to all the isolates of the disease organism and is often polygenically determined. With race specificity as the basis for distinction between the two types of resistance, once a pathogen isolate has overcome nonspecific horizontal resistance, it must be reclassified as specific or vertical. Specific resistance has also been defined as resistance to infection or hypersensitive resistance, while nonspecific or horizontal resistance permits infection but reduces the colonization or spread of the disease. This implies that intermediate levels of resistance must be horizontal; however, such resistance is race-specific. This chapter discusses the different types of race-specific resistance, their sources, and their use in developing rust resistant cultivars. Race-specific resistance includes hypersensitive and intermediate or moderate seedling resistance, mature- or adult-plant resistance, and resistance due to genes with an additive or cumulative effect. There is an increasing consensus that all types of resistance must be utilized in the development of a breeding strategy to produce cultivars with stable rust resistance.
Published Version
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