THE EFFECT OF TEMPERATURE ON INFECTION OF PLANT HOSTS BY PHYTOPHTHORA KERNOVIAE

Abstract

Phytophthora kernoviae has been reported to cause bleeding stem lesions and foliar necrosis on a wide range of species with little knowledge of the optimal conditions for infection. Sporangia and zoospores from six isolates of P. kernoviae were tested for germination on 20% V8 Agar plates. Both sporangia and zoospores germinated, despite sporangia showing significant differences between temperatures in the range 20-25°C (P<0.05). Detached leaves were inoculated with sporangia to measure the size of the necrotic lesion at temperatures between 20-25°C. Infection and foliar necrosis of detached plant material occurred optimally at 21°C on Rhododendron ponticum (P<0.001) and Magnolia stellata, but was insignificant on Viburnum tinus . Similar lesions were observed on detached leaves inoculated with mycelia plugs. Protein was isolated from P. kernoviae cultures grown at 20°C or 24°C and incubated on detached leaves of R. ponticum. While the secreted protein isolated from mycelia cultures grown at 20°C and 24°C had characteristics of a putative elicitin, only the crude secreted proteins isolated from 20°C cultures elicited host responses when applied to the detached leaf surface. Proteomic analysis confirmed that the putative 10-kDa protein isolated at both temperatures shared sequence homology to the conserved domain other known elicitins of Phytophthora spp. Other potential proteins were observed that could be contributing to regulation of infection, but their identification and activity is work for future studies.