INFLUENCE OF TEMPERATURE ON INTERACTION OF RESISTANCE GENES IN SPRING WHEAT DIFFERENTIALS WITH RACES OF COMMON BUNT (TILLETIA-TRITICI AND TILLETIA-LAEVIS)

Temperature affects the expression of resistance to common bunt and can influence the efficacy of tests to screen for resistance to this disease. A study was undertaken to determine the response of spring wheat differentials possessing bunt resistance genes to temperature and races of Tilletia tritici and T. laevis. Differential wheat lines carrying resistance genes Bt-2, Bt-7, Bt-8, Bt-9, and Bt-10, were individually inoculated with bunt races L3, T1, T15, and T27, and incubated at 8, 10 or 15 degrees C for 0-10 wk. Responses to bunt infection following low temperature incubation at 8, 10, and 15 degrees C differed among differentials carrying the Bt genes. The resistance of the Bt-10 differential was effective at all three temperatures for all incubation periods whereas the resistance in differentials carrying the Bt-2 or Bt-8 gene was effective at 15 degrees C but not at 8 degrees C and 10 degrees C. Resistance in the Bt-9 differential was ineffective at all three temperatures. The four races of common bunt were similar in their level of infection in the differentials carrying individual Bt genes at the different temperatures although some differences in infection levels were observed. A screening test consisting of 2-4 wk growth at 15 degrees C followed by growth to maturity in the greenhouse can identify wheat lines containing Bt-8 and Bt-10.