Allelic Relationship of A. strigosa Crown Rust Resistance Factors and their Relationship to Pc38 Suppression

Abstract

An investigation of the suppression effect of Pc38 on Pc94 was conducted by developing F2 segregating populations from genotypes possessing Pc38 and Pc94, together with a population void of the Pc38. Segregating phenotypic ratios were used to determine the crown rust resistance suppression at the Pc38 locus. A Leggett/Df-38 F2 population, possessing no Pc38 gene, produced resistant to susceptible ratios of 3:1 and 2:1. Leggett/Dumont and Leggett/Steele population possessing a copy of Pc38 each, produced resistant to susceptible ratios of 1:3, 1:2 and 3:13. Leggett was the resistant parent possessing Pc94 while Dumont and Steele were the susceptible parents possessing Pc38. Df-38, a susceptible parent, contained neither Pc94 nor Pc38. CR91 was used to identify resistant and susceptible plants in the segregating populations. A factor closely linked to Pc38 or the gene itself was confirmed to suppress the resistance effect of Pc94 in this study. A second experiment was conducted to determine the allelic relationship of crown rust resistance genes in 08BT26-2, 08BT70-1, BT1020-1-1 and BT1021-1-1. The genotypes possessed resistance genes introgressed from A. strigosa similar to Leggett. Leggett is homozygous for Pc94. Four different F2 segregating populations were developed from Leggett by 08BT26-2, 08BT70-1, BT1020-1-1 and BT1021-1-1. A crown rust race virulent to Pc94 was used to determine resistant to susceptible ratios of the populations. Crown rust race 16MN (100- 3) was used to discriminate between resistant and susceptible plants. The allelism test confirmed that the resistance gene present in 08BT26-2 and 08BT70-1 genotypes were the same as Pc94 in Leggett while genotypes BT1020-1-1 and BT1021-1-1 were different.