Evaluating the potential of environmentally friendly compounds to deactivate different life stages of Phytophthora species

Phytophthora species are a genus in the oomycete class and are destructive plant pathogens. The ability to inhibit all stages in the life cycle of these aggressive Phytophthora pathogens is essential for the long-term protection of native trees, plantation forests and horticultural crops that they threaten. Compounds having this ability are currently scarce. In this study, antifungal compounds of natural and synthetic origin were screened against the mycelial, zoospore and oospore life stages of Phytophthora agathidicida (P. agathidicida 18406), P. multivora (P. multivora 20280) and P. cinnamomi (P. cinnamomi 20276, 3910 and 21050). An antifungal lipopeptide showed promising (25-200 mu g/mL) antimycelial activity against all the tested Phytophthora species, rapid (c. 30 s) inhibition of P. agathidicida, P. multivora and P. cinnamomi 3910 zoospore motility, inhibition of zoospore germination at 12.5-50 mu g/mL and reduced the viability of P. agathidicida and P. multivora oospores at 1000 mu g/mL. Polygodial extracted from New Zealand horopito leaves showed more potent (5-50 mu g/mL) antimycelial activity and inhibited zoospore motility of P. agathidicida, P. multivora and P. cinnamomi 3910, although at a slightly slower rate; however, it was inactive against oospores. Polygodial and lipopeptide protected kauri and avocado leaves from Phytophthora infection and did not show symptoms of phytotoxicity. Polygodial also inhibited the growth of P. agathidicida in soil. This study demonstrates for the first time the promising antioomycete potential of compounds ranging from small molecule natural products to larger biomolecules such as lipopeptides, which can be developed as compounds to deactivate the different life stages of aggressive Phytophthora species.