The effects of neem [Azadirachta indica A. Juss (meliaceae)] oil on Fusarium oxysporum f. sp. medicagenis and Fusarium subglutinans and the production of fusaric acid toxin

Fungi of the genus Fusarium are well known plant pathogens, cause several vascular diseases and are producers of toxins. In vitro assays evaluated the effects of Neem (Azadirachta indica) oil on the diameter of colonies, dry weight, spore production, spore viability and production of Fusaric Acid toxin on Fusarium oxysporum f. sp. medicagenis and Fusarium subglutinans isolates. Effects of Neem oil were analyzed at concentrations 0.25%, 0.5% and 1% in Czapek Yeast Agar medium. The production of Fusaric acid was determined by Thin Layer Chromatography and quantified by UV spectrophotometry. Neem oil showed inhibitory effects on the isolates tested, although they varied according to type of isolate and oil concentration. Neem oil was efficient in reducing the colonies' diameter and dry weight in concentration-dependent manner. Neem oil was efficacious at higher concentration in the decrease of sporulation. Spore germination was affected by Neem oil when the spore was grown in Neem-contained medium as when the spore emerged from a culture in a Neem medium. Neem oil decreased and even inhibited the production of Fusaric acid by the assayed isolates. Since these isolates are plant pathogens and producers of Fusaric acid, Neem oil may be introduced as an integral item in the management of host plants.