THE INDUCTION OF PHENOLIC-COMPOUNDS IN RICE AFTER INFECTION BY THE STEM NEMATODE DITYLENCHUS-ANGUSTUS

Changes in the phenolic profiles of five resistant and two suspectible varieties of deep water rice were examined following infection by the rice stem nematode Ditylenchus angustus. Within resistant cultivars, inoculated plants were either symptomless or exhibited symptoms of inc ompatible (resistant), compatible (suspectible) or partially compatibl e responses. Extracts of leaf tissues from inoculated and uninoculated plants were made in methanol (80% v/v) and analysed by reverse phase HPLC. Tissues from inoculated plants with and without symptoms were ex amined separately Traces revealed the presence of 13 to 18 UV absorbin g constituents of rice leaf extracts, depending on the variety. Chloro genic acid occurred in small amounts and only in resistant plants, but there was no correlation between constitutive compounds and resistanc e or susceptibility. The secondary chemistry of tissues exhibiting sym ptoms changed in all resistant varieties. Levels of chlorogenic acid i ncreased in response to infection. Furthermore in two resistant select ions of rice variety Rayada 16-06, a newly formed compound, the rice p hytoalexin sakuranetin was also isolated. There was correlative eviden ce that both of these compounds could have a functional role in resist ance. At 5 days after inoculation the concentrations of sakuranetin in Rayada 16-06 were 8 & 13 mu g/g leaf in plants with 10 and 200 D. ang ustus/plant, respectively No change in secondary chemistry occurred in susceptible varieties.