Genetics of resistance to Puccinia graminis f. sp. secalis in Barley line Q21861

Barley line Q21861 (PI 584766) possesses rpg4, a recessive gene that confers resistance to pathotype Pgt-QCCJ of Puccinia graminis f. sp. tritici, the wheat stem rust pathogen. Q21861 also possesses resistance to P. graminis f. sp. secalis, the rye stem rust pathogen. To determine the genetics of rye stem rust resistance in this line, a doubled haploid (Q21861/SM89010) and three different F₃ (Steptoe/Q21861, Q21861/SM89010, and Q21861/Klages) populations derived from Q21861 were evaluated to isolate 92-MN-90 of P. graminis f. sp. secalis at the seedling stage. The number of resistant and susceptible progeny in the doubled haploid population fit a 1:1 segregation ratio, indicating that a single gene conferred resistance to the rye stem rust pathogen. This result was confirmed from the 1:2:1 segregation ratio of homozygous resistant, segregating, and homozygous susceptible F₃ families in the three other populations. The resistance gene was partially dominant, based on the infection types of F₁ plants from the cross Q21861/Steptoe. Data for reaction to P. graminis f. sp. secalis were compared with those obtained in response to P. graminis f. sp. tritici (pathotype QCCJ) on remnant progeny from all four populations. Resistance to P graminis f. sp. secalis cosegregated with resistance to P. graminis f. sp. tritici, suggesting that the gene conferring resistance to the former is at the rpg4 locus in barley line Q21861.