The influence of nitrogen nutrition on the sensitivity of tomato plants to culture filtrates of Fusarium and to fusaric acid

Abstract

High (420 and 630 ppm) and to a lesser extent very low (70 ppm) levels of fertilization with nitrate-nitrogen decreased the sensitivity of tomato plants to fusaric acid as well as to culture filtrates of Fusarium oxysporum f. sp. lycopersici R1. There was a positive correlation between the external symptoms produced (chlorosis, necrosis and epinasty) and the concentration of the toxin or culture filtrate used which varied with the nitrogen regime under which plants were grown. Leakage of electrolytes, from leaf discs of plants grown with various levels of nitrogen fertilization, was measured in the presence of fusaric acid. Membranes of cells from plants grown at high doses of nitrate-nitrogen were less sensitive to the toxin, and the variation in reaction of cells from plants grown with different levels of nitrate-nitrogen appeared to be directly correlated with the resistance of such plants to infection with F. oxysporum f sp. lycopersici. The decreased susceptibility of tissue to fungal infection is probably the consequence of the reduced sensitivity of the host plant membranes to toxic substances produced by the fungus. The importance of this type of non-specific resistance in pathogenesis is discussed.