Summary: Mechanical damage to hyphae of some A2 compatibility-type Phytophthora spp., by cutting with a cork borer or scalpel, can induce formation of pairs of gametangia followed by oospores. The A1 compatibility types examined did not respond significantly to damage. Two homothallic species of Phytophthora responded to mechanical damage by forming increased numbers of gametangia. Induction of gametangia in A2Phytophthora cinnamomi following damage depends on the composition of the medium. Injury produced by H2O2 or ether also induced sexual reproduction in A2P. cinnamomi. It is concluded that the mechanism by which gametangia are induced in A2 Phytophthora strains by Trichoderma viride may involve damage and that production of oospores in response to damage may be significant in the survival of Phytophthora.
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