Abstract: This work aimed to study the inhibitory effect of L-cysteine against Alternaria alternata rot of grapes. The fungus was treated with different concentrations (0.4, 0.6, 0.8, 1.0, 1.2, 1.4, 1.6, 1.8, 2.0, 2.2, 2.4, 2.6, 2.8 and 3.0 g/L) of L-cysteine, and that without any treatment was regarded as the control group. The antifungal effect of L-cysteine was evaluated by determining the inhibition rates of colony growth, spore germination and germ?tube?elongation as well as using inverted microscopy to observe mycelial morphology. The appropriate concentrations of L-cysteine were selected to treat grapes inoculated with Alternaria alternate, which were subsequently stored in an incubator at 25 ℃. The inhibitory effect of L-cysteine on Alternaria alternata rot was researched by measuring the diameter of lesions, incidence and related enzyme activities. Results showed that compared with?the control?group, L-cysteine at all concentrations could significantly inhibit mycelial growth and germ tube elongation and reduce the rate of spore germination. In addition, L-cysteine could decrease the diameter of lesions and the rot rate of fruits, delay the accumulation of malondialdehyde (MDA) and maintain high antioxidant activity as well, being the most effective at a concentration of 2.8 g/L.

Key words: L-cysteine, Alternaria alternata, Alternaria alternata rot, grape, inhibitory effect