Pyramiding Major Genes for Resistance to Maintain Residual Effects

Abstract

In 1978, R. R. Nelson (26) concluded his chapter in a previous volume of the Annual Review of Phytopathology entitled Genetics of Horizontal Resis­ tance with the advice, Go back young man and gather up your weary and defeated genes of the past, take your currently successful genes, find some new ones if you can, and build yourself a pyramid. Nearly ten years later, it is our privilege to take another look at that counsel. A number of papers have been published that deal with the effects resistance genes confer when in­ oculated with compatible isolates of the pathogen (2, 6, 8, 20-25, 28, 29, 31, 32). Reviews of some of this literature have already appeared (9, 16, 26, 27). Despite this important progress, plant pathology is still not at a point where the notion of pyramiding resistance genes to provide durable resistance to both virulent and avirulent races of a pathogen is widely accepted. We feel that the research that has been accomplished can be divided into three categories. The initial research, much of which has been completed, focused on determining if host genes do confer resistance to isolates of a pathogen that