Polygenic Resistance to Plant Disease and Its Use in Breeding Resistant Cultivars

Abstract

AbstractRace nonspecific, generalized or horizontal resistance (HR) usually is inherited polygenically. Polygenic resistance (PR) acts retarding the rate of development of the epidemic rather than in delaying its onset. Years of experience with economically important plant diseases has shown that, although small amounts of disease can be expected to occur, PR is adequate to protect crops from serious losses under normal field conditions. In most cases studied, PR has not been rendered useless due to changes in the pathogen, as has been characteristic of oligogenic resistance (OR); thus, it probably can be expected to give lasting protection. Polygenic resistance may operate through many mechanisms, and may be governed by genes that are not specifically concerned with disease, but which regulate basic processes of the plant. Other disease control measures, such as use of fungicides and OR, often can be combined advantageously with PR. The heritability of various manifestations of PR, and of similarly inherited disease tolerance, to several important diseases is sufficiently high to make selection for it practical. Recognizing and recovering PR from hybrid populations may require special methods, and may be relatively difficult and expensive, but should be rewarding.