Glutathione alterations in melon and tomato roots following treatment with chemicals which induce disease resistance to Fusarium wilt

Abstract

Glutathione (GSH) has been implicated in the activation and regulation of the biosynthetic processes involved in plant defence. In this study, we examined whether herbicides which induce resistance to Fusarium sp. alter GSH concentrations in roots of cantaloupe melons and tomato. GSH levels were estimated spectrofluorimetrically in extracts from melon (8 days) and tomato (10 days) roots from plants grown in sand amended with various concentrations of the dinitroaniline herbicides trifluralin, oryzalin and dinitramine; the chloracetimide herbicide, acetochlor; and the chloracetimide safeners, flurazole and dichlormid. At the same time, treated and control tomato and melon seedlings were inoculated with their respective pathogens, Fusarium oxysporum f. sp. lycopersici and f. sp. melonis , and then planted into chemical-free Promix under controlled environmental conditions. Subsequent disease incidence was determined daily for 2 weeks. In dinitroaniline-treated tomato seedlings GSH levels were significantly higher than in control plants from the first harvest. This difference increased with time because herbicide treatment also reduced the rate of GSH decline. The extent of GSH increase was influenced by the chemical and the rate applied. All dinitroaniline treatments tested resulted in elevated levels of GSH in tomato and provided partial or complete protection against F. oxysporum f. sp. lycopersici Acetochlor, however, did not alter GSH levels in tomato, nor did it protect against F. oxysporum f. sp. lycopersici . In contrast, acetochlor was most effective in increasing GSH levels in melons and in providing protection against F. oxysporum f. sp. melonis . Oryzalin was the least effective in enhancing GSH and providing disease protection in melons. Neither dichlormid nor flurazole greatly altered GSH concentration or protected either plant species from disease. A highly significant inverse correlation was observed between the GSH levels and disease incidence with the chemicals tested.