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New Zealand Plant Protection 67 (2014): 54-59

Pathogenicity of four Phytophthora species on kauri: in vitro and glasshouse trials

I.J. Horner and E.G. Hough

ABSTRACT

In kauri forest soils surveys, Phytophthora taxon Agathis (PTA), P. cinnamomi, P. multivora and P. cryptogea were detected frequently. In vitro and glasshouse studies determined that all four Phytophthora species produced lesions on excised kauri leaves and stems. Lesion advance was significantly slower with P. cinnamomi, P. multivora and P. cryptogea than with PTA. When 2-year-old kauri seedlings were trunk-inoculated, lesion spread was rapid with PTA, trunks were girdled, and all trees died within 4-6 weeks. Phytophthora cinnamomi, P. multivora and P. cryptogea produced substantially smaller lesions than PTA, no trees died, and plant growth was only slightly suppressed. Following soil inoculation with PTA, all kauri seedlings died within 10 weeks. There were no deaths following soil inoculation with P. cinnamomi, P. multivora or P. cryptogea, although feeder root damage was observed and the respective pathogens were re-isolated. Results suggest that PTA is an aggressive pathogen, and the other three species are weaker pathogens of kauri.

Keywords: Phytophthora, kauri, pathogenicity.

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