Histochemical comparison of the nonhost tomato with resistant wheat against Blumeria graminis f. sp. tritici

Abstract

The nonhost interaction of tomato-Blumeria graminis f. sp. tritici (Bgt) and resistant host interaction of wheat-Bgt were compared histochemically. The percentage of appressorium formation had no significant difference on tomato and wheat leaves. Papilla formation occurred earlier and more on host wheat than on nonhost tomato leaves, while the incidence of hypersensitive cell death was much higher in the nonhost interaction. Whole-cell H2O2 accumulation and hypersensitive cell death usually appeared in haustorium-invaded wheat epidermal cells. In contrast, the vast majority of non-haustorium epidermal cells were associated with H2O2 accumulation and hypersensitive cell death on tomato. Localized H2O2 accumulation and hypersensitive response were detected in effective papillae in both interactions. The peak percentage of haustorium formation was less than 7% in the nonhost interaction while reached 43% in the incompatible host interaction. These results indicate that hypersensitive cell death and papillae are likely to play an important role in preventing Bgt penetration and development on tomato and wheat leaves, both defense responses involving H2O2 accumulation. This study further implies that the nonhost and incompatible interactions share similar cytological mechanisms.