Responses of embryogenic mango cultures and seedling bioassays to a partially purified phytotoxin produced by a mango leaf isolate of Colletotrichum gloeosporioides penz

Summary Colletotrichum gloeosporioides Penz., the causal agent of mango anthracnose, produces a phytotoxin in vitro. The partially purified phytotoxin, presumably colletotrichin, caused anthracnose-like symptoms on young mango leaves, was toxic to embryogenic suspension cultures of two mango cultivars, ‘Hindi’ and ‘Carabao,’ and inhibited in vitro seed germination of two nonhosts, lettuce and tobacco. There were linear relationships between concentration of the partially purified phytotoxin and mortality of mango embryogenic cultures. Embryogenic cultures grown in the presence of the partially purified phytotoxin showed significantly lower growth rates than the controls. Similarly, embryogenic cultures grown in the presence of 40% (vol/vol) fungal culture filtrate showed significantly lower growth rates than unchallenged controls. Medium containing 40% (vol/vol) Czapek-Dox fungal broth did not reduce growth of embryogenic cultures, indicating the production of phytotoxin in vitro. The results suggest that either fungal culture filtrate or purified phytotoxin can be used as in vitro selection agents to screen for resistance to this fungus.