Genetic Control of Phenotypes in Wheat Stem Rust*

Abstract

Progress in understanding the genetic control of phenotype in the interaction of Puccinia graminis Pers. f. sp. tritid and Triticum sp. has been slow. In 1866, de Bary (10) showed that Aeddum and P. graminis were actually the same organism. The study of genetics dates back to Mendel (38), and not until 40 years later did Biffen (2) show that host resistance to stripe rust was inherited in a Mendelian manner. Eriksson & Henning (14) and Stakman & Piemeisel (58) showed that variation for virulence existed within P. graminis for both host species and cultivars, respectively. Then in 1927, Craigie found that the sexual recombination of the fungus occurred on the barberry (8). Following Craigie's work many others have attempted genetic studies of P. graminis. Among the first and most successful was the team of Margaret Newton & Thorvaldur Johnson (24, 40, 41). The single most important cross was made by Loegering & Powers (32), who had the insight and techniques to maintain living uredospores of the parents, the F and F2 progeny. The host-pathogen interaction generally produces a visible response. This response is the result of the interaction of the host and pathogen genotypes and the environment existing immediately before and following infection (52). The host-pathogen interaction is expressed as an infection type (Table 1). The compatible and incompatible host-pathogen interactions are called high and low infection types, respectively (28-30).