Fusaric acids in relation to mycoherbicidal activity of Fusarium oxysporum isolates against the parasitic weed Orobanche crenata.

Abstract

usarium oxysporum represented the second highest number of Fusarium isolates obtained during a survey on dominant fungal pathogens infecting young legume broomrape plants infesting faba bean fields in El-Fayoum and Bani-suef governorates. F. oxysporum isolates scored 28 % (11 isolates) following F. solani which scored 32 % (12 isolates) of the total Fusarium. Culture filtrates of F. oxysporum isolates showed different phytotoxic activity against the germination of O. crenata seeds in vitro and inhibition values ranged between 20 and 69 %. No significant difference was recorded when the bioassay was carried out with organic extracts of these culture filtrates and inhibition values ranged between 23 to 71 %. Tests of pathogenicity carried out in pots did not also show a significant difference where virulence of F. oxysporum isolates ranged between low (1 = light browning) and high (4 = 100 % browning plus wet rot) when the pathogenicity was rated on a scale depended on the color progress and tissue rotting in inoculated O. crenata tubercles attached to V. faba roots. The content of fusaric and dehydrofusaric acids quantified by high performance liquid chromatography (HPLC) in Fusarium culture filtrates were related to their phytotoxic activity and virulence. A negative correlation (- 0.479 and 0.393) was found between the content of both acids and the biological activity of the tested filtrates of fungal liquid cultures.