Effects of fusaric acid on cells from tomato cultivars resistant or susceptible to Fusarium oxysporum f sp lycopersici

Cell suspension cultures were set up from two tomato cultivars, one resistant, ('Rio grande') and one susceptible ('63.5') to Fusarium oxysporum f. sp. lycopersici. Growth rates of the two cell cultures were comparable. Toxicity of fusaric acid, expressed as the fresh weight loss, was analyzed: It was significant in both cases after 10 h, but toxicity was twice as high for '63.5' suspension cells. In the same way, electrolyte leakage caused by fusaric acid was three times more important for '63.5' suspension cells. Moreover, fusaric acid treatment resulted in an acidification of the extracellular medium for '63.5' suspension cells (0.4 pH unit), whereas an alkalization was observed for 'Rio grande' suspension cells (0.2 pH unit). Preliminary experiments suggest that fusaric acid was partially metabolized by 'Rio grande' suspension cells, however, no detoxified forms of fusaric acid were detected either in cells or in culture filtrates. For these two tomato cultivars, the differences in sensitivity to fusaric acid of cultivated cells correspond to the differences in plant susceptibility to Fusarium oxysporum f. sp. lycopersici.