Leaf epicuticular wax ultrastructure and trichome presence on Russian wheat aphid (Diuraphis noxia) resistant and susceptible leaves

摘要

The Russian wheat aphid (Diuraphis noxia) was first discovered on wheat in South Africa during 1978. It has since become a serious pest. The leaf epicuticular wax ultrastructure and leaf trichomes were examined on two Russian wheat aphid-susceptible wheat cultivars ('Palmiet' and 'Tugela') and a Russian wheat aphid-resistant wheat cultivar ('Tugela DN'). The lengths of the trichomes showed no significant differences in the three wheat cultivars examined. The resistant cultivar ('Tugela DN') had a significantly greater trichome density compared to the susceptible cultivars. Examination of the position of the trichomes revealed that there were differences for the adaxial and abaxial surfaces. Trichomes on all three wheat cultivars were found to occur mostly on the leaf veins of the adaxial surfaces, and on the leaf veins as well as between them on the abaxial surfaces. Leaf trichome density and position may act as a physical obstacle to Russian wheat aphid feeding as the aphid feeds on leaf veins of the adaxial leaf surfaces. The high trichome density on the leaf veins found in the resistant 'Tugela DN' cultivar could prevent the Russian wheat aphid from finding a suitable feeding site. Comparison of the scanning electron micrographs showed that the epicuticular wax structure was similar on both the adaxial and abaxial surfaces amongst the three wheat cultivars, and does not seem to affect Russian wheat aphid feeding.