Soil drenching with water extracts of Oxalis articulata savigny suppress fusarium wilt of tomato [Lycopersicon esculentum]

Previous studies have suggested strong antifungal activity of Oxalis spp. extracts on some soil-borne plant pathogenic fungi including Fusarium oxysporum. The present experiment was conducted to test the effects of the dry leaf extracts of shamrock oxalis (O. articulata) on Fusarium wilt (caused by F. oxysporum f. sp lycopersici) on tomato (Lycopersicom esculentum) under greenhouse conditions. No damage was observed on the inoculated tomato plants treated with Oxalis extract previously, and the effects of the extract were comparable to those of the commercial fungicide, benomyl. Activity was not dependent on oxalate, suggesting that either the other antifungal substances act against F. oxysporum or the water extracts of O. articulata induce resistance to the pathogen in tomato. Agrochemicals such as fungicides, herbicides and insecticides have improved agricultural works and products, but have also caused serious problems such as environmental pollution and detrimental effects on human health (Marcheterre et al. 1985; Aoyama & Nugumo 1996; Campbell et al. 1996; Epstein & Bassein 2001). Environmental pollution and possible damage to human health and ecosystems have been driving force behind the reevaltution of the application dose of agrochemicals, and the quest co find new alternatives to these chemicals. Recent studies showed antimicrobial activities of natural products (Satish et al. 1999; Ara et al. 2001) and effectiveness on the suppression of plant disease (Nakabayashi & Fukuda 1999; Bowers & Locke 2000; Stavroula & Tzempelikou 2000) . Extracts from some plant species have been reported to induce the production of phytoalexins and resistance of host plants to pathogens (Doubrava et al. 1988; Daayf et al. 1997; Toal & Jones 1999).These phytochemicals are potential alternatives to agrochemicals in sustainable agriculture. Phytochemicals are useful materials from the viewpoint of optimizing the use of plant resources. Results of the laboratory experiments revealed that water extracts from leaves and tubers of Oxalis spp., known as common weeds or ornamental plants, suppressed spore germination or mycelial growth of some soil-borne plant pathogenic fungi (Shiraishi et al. 2001). However, the suppressive effects against disease in soil were unknown. The aim of the present work was to evaluate water extracts of O. articulata applied to soil for their ability to suppress Fusarium wilt of tomato. Plant diseases caused by F. oxysporum are widespread in the world. These pathogens cause chlorosis and wilt on vegetables, grains and trees. They inhibit growth of host plants and eventually cause plant death. F. oxysporum can survive for a long period in soil without host plants. Due to the form tolerant structures called chlamydospores, plant diseases caused by these fungi are diffrcult to control with fungicides or crop rotation in general. Hence, a new management system is required to control disease.