Chemical factors of the leaf surface involved in the morphogenesis of Blumeria graminis

Abstract

The epidermal surface and the wax of leaves of barley (Hordium vulgare) induced appressorium (APP) differentiation of the fungus of Blumeria graminis f. sp. hordei. The epidermal surfaces and waxes of non-host plants, on the other hand, induced less APP differentiation in this fungus. Bioassays of thin-layer chromatographic (TLC) fractions of barley wax revealed that the highest APP differentiation-stimulating activity was in the aldehyde fraction. Gas liquid chromatographic analysis of barley aldehydes showed that the main aldehyde was that with a C26 chain length. The amount of aldehydes in wax of cabbage, a non-host plant of B. graminis, was greater than that in wax of barley in TLC spots. However, the main aldehydes in cabbage wax were those with C28 and C30 chain lengths. In the wax from tobacco, also a non-host plant of B. graminis, the amount of aldehyde in TLC spots was much less, although the main aldehyde was that with a C26 chain length as was found in barley aldehydes. Chemically synthesized C26 aldehyde showed the potential to strongly induce APP differentiation of B. graminis. Therefore, it was concluded that C26 aldehyde, a component of barley wax, is the factor highly responsible for the APP differentiation of B. graminis.