Submitted to: Encyclopedia of Plant Pathology
Publication Type: Book / Chapter
Publication Acceptance Date: 9/1/2000
Publication Date: N/A
Technical Abstract: The term 'differential variety' is used in the plant pathology literature t designate varieties that show clear differential reactions to different pathotypes of a pathogen. As an example, Varieties A and B are differential varieties if A is resistant to pathotype 1 but susceptible to pathotype 2 while B is susceptible to pathotype 1 but resistant to pathotype 2. Differential reactions of varieties and pathotypes were first recognized in 1911. Since then, sets of differential varieties have been established to designate pathotypes for many different plant pathogenic fungi. Standard sets of differential varieties are used to characterize distribution and frequency of pathotypes to aid in developing disease resistant crop varieties that will perform consistently across locations and from year to year. They also allow plant pathologists to track changes in virulence gene frequency and document long-distance movement of pathogen populations. For maximum value, sets of differential varieties should consist of near-isogenic lines, each with a different single gene for resistance.