Key infection stages defending heat stress in high-temperature-resistant f. sp. isolates.

With the increase of temperature in the winter wheat-growing regions in China, the high-temperature-resistant f. sp. () isolates developed in the fields. To clarify the key infection stages and the roles of heat shock protein (HSP) genes of high-temperature-resistant isolates defending high temperature, 3 high-temperature-resistant and 3 sensitive isolates were selected from 55 isolates after determination of temperature sensitivity. And then they were used to investigate the infection stages and the expression levels of genes, including , , and , at 18°C and 25°C. The formation frequency of abnormal appressoria and inhibition rate of haustoria formation of high-temperature-resistant isolates at 25°C were lower than those of high-temperature-sensitive isolates, while major axis of microcolonies of high-temperature-resistant isolates was higher than those of high-temperature-sensitive isolates at 25°C. The results indicated that haustoria formation and hyphal expansion were the key infection stages of defense against heat stress in high-temperature-resistant isolates. Further analyses of genes found the expression levels of and were upregulated at 24 and 72 h post-inoculation in high-temperature-resistant isolates, while no significant difference was observed for and genes. Taken together, the basis of high-temperature-resistant isolates is associated with induced expression of and response to heat stress in haustoria formation and hyphal expansion stages.