Effects of chrysophanol, parietin, and nepodin of Rumex crispus on barley and cucumber powdery mildews

Three substances that show antifungal activity against Blumeria graminis f. sp. hordei were isolated from roots of Rumex crispus and identified as chrysophanol, parietin, and nepodin. The substances were tested for plant disease control activity in vivo against six plant pathogenic fungi. All specifically reduced the development of barley powdery mildew. The concentrations required for 50% disease control were 4.7 mug/ml for chrysophanol, 0.48 mug/ml for parietin, and 20 mug/ml for nepodin. These agents showed both curative and protective activity against barley powdery mildew. Chrysophanol (100 mug/ml) and nepodin (400 mug/ml) were more effective than the fungicides fenarimol (30 mug/ml) and polyoxin B (100 mug/ml), under glasshouse conditions, against cucumber powdery mildew, which is caused by Podosphaera xanthii. Parietin (30 and 10 mug/ml) reduced the development of cucumber powdery mildew as efficiently as fenarimol (30 mug/ml) and more effectively than polyoxin B (100 mug/ml). (C) 2004 Elsevier Ltd. All rights reserved.