Effects of epicuticular wax from Digitaria sanguinalis and Festuca arundinacea on infection by Curvularia eragrostidis

Epicuticular wax is a plant's initial defence system to various foreign invasions, including invasion by fungi. In this study, we investigated the effect of epicuticular wax of Digitaria sanguinalis and Festuca arundinacea on invasion by the fungus Curvularia eragrostidis and the difference in components of epicuticular waxes between the two plants. The epicuticular wax of D. sanguinalis (host) significantly enhanced the growth of germ tubes of C. eragrostidis conidia, but had no effect on appressorium formation. However, the epicuticular wax of F. arundinacea (non-host) inhibited the extension of germ tubes and the differentiation of appressoria. Analysis using gas chromatography-mass spectrometry indicated that the constituents of these two epicuticular waxes were remarkably different. Among the 24 and 21 compounds found in the wax of D. sanguinalis and F. arundinacea, respectively, only four were the same. (Z, Z)- 9,12-Octadecadien1-ol constituted 54.3% of the total wax of D. sanguinalis, while 9-tricosene accounted for 49.8% of the total waxes of F. arundinacea. Furthermore, an extracellular esterase preparation from C. eragrostidis conidia could completely degrade the epicuticular wax of D. sanguinalis after 4 h incubation at 25 degrees C, but only partially degrade the wax from F. arundinacea. These results suggest that the components of the wax and their chemical characteristics are important in determining how effectively these plants are able to combat invasion of C. eragrostidis.