Temperature-sensitivity of the expression of resistance to Puccinia graminis conferred by the Sr15, Sr9b and Sr14 genes in wheat

Primary leaves of seedlings with different genetic backgrounds were inoculated with avirulent strains and then incubated in growth cabinets at constant temperatures of 15, 18, 22, 26 and 30 °C. Infection types in Sr15-bearing seedlings were low at 18 °C and below, mesothetic at 22 °C and high at 26 °C and above. Infection types in Sr14-bearing seedlings were high in most replicates at 15 °C and low at 22 °C and above; necrosis occurred in some replicates at 15 °C and all replicates at 18 °C and above. Infection types in Sr9b-bearing seedlings differed between the two strains of rust fungus used. With one strain, infection types decreased with increasing temperature from 18 °C; with the other strain, infection types decreased slightly at 30 °C. These observations are discussed in relation to others demonstrating two patterns of temperature sensitivity and then for their implications for hypotheses about the molecular bases of parasite--host interactions.