Cosegregation of Avr4 and Avr6 in Phytophthora sojae

Abstract

The F2 progeny resulting from a cross of Phytophthora sojae race 2 (avirulent on Rps4 and Rps6) and race 7 (virulent on Rps4 and Rps6) were tested for their ability to cause disease on soybean plants carrying the Rps4 or the Rps6 resistance genes. Of 55 F2 progeny analyzed, 41 individuals were avirulent on both of these genes and 14 were virulent on Rps4 and Rps6, indicating that avirulence on Rps4 and Rps6 is dominant and linked. These results support the suggestion that the soybean–Phytophthora relationship is a gene for gene interaction and that the presumptive Avr4 and Avr6 genes are either tightly linked or identical. Keywords: avirulence, genetic mapping, Glycine max, incomplete dominance, Phytophthora megasperma f.sp. glycinea.