THE INFLUENCE OF CYSTEINE, CYSTEINE ANALOGS, AND OTHER AMINO-ACIDS ON SPORE GERMINATION OF ALTERNARIA SPECIES

The influence of amino acids on spore germination of Alternaria cassiae was investigated to develop a basis for improvement of mycoherbicide formulations. At a 1% concentration, the majority of amino acids exhibited little or no effect on spore germination in vitro. However, aspartic and glutamic acids stimulated germination, and serine, tryptophan, cysteine, and phenylalanine inhibited spore germination. Cysteine was the strongest inhibitor of germination and was active in the presence of potato dextrose broth, which is normally stimulatory. One percent cysteine reduced germination 96% after 4 h. Derivatization of the mercaptan or amino group but not the carboxylic acid group diminished the ability to inhibit spore germination. Cysteine also inhibited spore germination of Alternaria crassa and Alternaria macrospora. Application of cysteine reduced development of Alternaria leaf spot on cotton plants inoculated with A. macrospora. The results demonstrate diverse effects of amino acids on spore behavior and suggest cysteine or similar compounds may be useful in preventing diseases caused by Alternaria species.