Identification of a microsatellite marker associated with stem rust resistance gene Sr35 in wheat

A segregating population from the cross '2137'/CRL-Sr35 was made to identify molecular markers linked to the stem rust resistance gene Sr35 that provides resistance against many devastating races, including QTH and TTKS (or Ug99), in wheat. Ninety-eight F-2 plants were inoculated with a stem rust isolate of race QTH. Infection type and severity were evaluated 10 days after inoculation. Twenty-one microsatellite primer pairs were tested for polymorphism among parental lines and F-2 population. Resistance was conferred by a dominant gene (chi(2)= 1.01, P=0.48). Out of four primer pairs (Xgwm155, Xgwm391, Xgwm497 and Xfca2076) only two markers (i.e. Xgwm391 and Xcfa2076) retained significance at alpha = 0.05. GWM391 revealed a polymorphic fragment of 200 bp found only in the susceptible bulk and 2137. In contrast, Xcfa2076 amplified polymorphic fragments of 210 bp in the resistant bulk and CRL-Sr35. Using linkage analysis Xgwm391 was found to be relatively close to Sr35 with a genetic distance of 12.2 cM. Although they have not retained significance at alpha = 0.05, the markers Xgwm155 and Xgwm497 have genetic distances of 4.6 and 12.1 cM from the Sr35 gene. While searching for closer marker continues, wheat breeders should be obviously benefited by using these markers in their selection of Sr35 in their battle against the brutal stem rust race Ug99. Further mapping attempts in this chromosomal region with more markers and larger F-2 and/or F-2:3 sample sizes are warranted to identify closer and more efficient markers for Sr35.