Studies On Chemical Induction Of Melon Resistance To Powdery Mildew:Elicitor Screening And Physiological Mechanism

The five chemicals, induction effect on resistance to powdery mildew of melon were systemically compared in melon leaves which planted on greenhouse. Effects of BTH spaying on induced resistance to powdery mildew (Erysiphe cucurbitacearum) of melon were studied on three melon cultivars with different resistance levels. Effects of BTH spaying on induced resistance to powdery mildew (Erysiphe cucurbitacearum) were studied at three stages of melon plants treated with BTH and then inoculated with Erysiphe cucurbitacearum.1. The results showed that BTH,SA,OAA and Na₂SiO₃ have significant induction effects. The best concentration on induced resistance of them is 0.25 mmoL/L ,1.0 mmoL/L,30 mmoL/L and 10 mmoL/L respectively, and induction effect is 72.4%,49.9%,43.4% and 34.9% respectively, whereas the induction effect of K₂HPO₄ is not significantly.2.The changes in activities of phenylalanine chitinase(CHI) ,1,3-β-glucanase(GLU), phenylalanine ammonialyase(PAL) and polyphenoloxidase(PPO) in melon leaves treated with five chemical elicitors and inoculated with powdery mildew were analyzed to explore the physiological and biochemical mechanisms of five chemical elicitors induced systemic acquired resistance (SAR).No significant difference in the PPO activity was observed between five elicitors treated and untreated after inoculation with powdery mildew.However,the CHI activity in the leaves did not show any remarkable changes upon chemical elicitors treatment and inoculation with powdery mildew,except for the elicitors SA and K₂PO₄3. Positive correlations existed between the induction effect and the intrinsic resistance to powdery mildew of melon cultivars. The resistant cultivars showed higher induced resistance to powdery mildew and higher increase rate of leaf GLU and PAL activity than tolerant and susceptible cultivars. Leaf activities of GLU,PAL and PPO in melon plants treated with BTH and then inoculated with Erysiphe cucurbitacearum were higher than in plants only inoculated. Ultra-structure observation showed that papilla may be an active responsive structure of melon leaves to Erysiphe cucurbitacearum, the papilla structures in the disease resistant cultivar was hemispherical type but was cylinder type in the tolerant and susceptible cultivars.4. Melons in the tendril and young plant stages demonstrated higher induction effect than those at the young fruit stages.But induction effect is not significantly between melon in the tendril and young plant stages. The increase rate of GLU activity of melon leaves in the young plant stages is the biggest.and the activity climax of PAL is postponed with the increase of plant ages.