| Abstract
| - Resveratrol is a phytoalexin produced in different unrelated plant species such as grapevine andpeanut. The effect of resveratrol and its glucoside trans-resveratrol-3-O-β-d-glycopyranosid (piceid)against Venturia inaequalis, the causal agent of apple scab, was evaluated using a newly establishedtest based on enzymatically isolated cuticular membranes (CMs) from apple (Malus domestica Borkh.)leaves. The test substances resveratrol and piceid were either sorbed to CMs before inoculationwith spores or were applied simultaneously with the Venturia inaequalis spores to the CMs, and theireffect on germination, appressoria formation, and penetration was examined. Resveratrol had noinfluence on spore germination but a significant inhibiting effect on penetration when appliedsimultaneously as well as before. A percentage inhibition of 89.7 ± 11.5 and 61.8 ± 35.1 was observedfor simultaneous and preapplication, respectively. The resveratrol glucoside piceid had a significantinhibitory effect on germination and completely inhibited penetration of the fungus at concentrationsbetween 200 and 400 μg mL-1 when applied simultaneously with the spores to the CMs. On piceid-enriched CM (preapplication), spores germinated but penetration was inhibited nearly completely(96.1 ± 5.1%). Thus, in vitro experiments showed that resveratrol and its glucoside in fact couldcontribute to improving the pathogen resistance of apple leaves. Keywords: fungal pathogen; isolated cuticular membrane; penetration; phytoalexin
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