VIEW ARTICLE

Ecology and Epidemiology

The Effect of Temperature on Growth and Pathogenesis of Phytophthora cinnamomi and on Growth of Its Avocado Host. G. A. Zentmyer, Professor and plant pathologist. Department of Plant Pathology, University of California, Riverside 92521; Phytopathology 71:925-928. Accepted for publication 26 January 1981. Copyright 1981 The American Phytopathological Society. DOI: 10.1094/Phyto-71-925.

The growth curve of Phytophthora cinnamomi in response to temperature was similar to that of the avocado (Persea americana) host except at 33 C where the host grew well but the pathogen was inhibited both in growth and in sporangium production. Development of Phytophthora root rot and consequent reduction of growth of avocado seedlings was greatest at soil temperatures of 21 and 27 C under controlled conditions in naturally infested soil. Some disease developed at 15 C; at 33 C, the fungus was not pathogenic and did not affect growth of the avocado. There was a positive correlation (R = 0.966, significant at P = 0.05) between the reduction in root weight at the different temperatures and growth of P. cinnamomi at those temperatures. In the absence of the pathogen, water use by the avocado seedlings was related to top growth. In the presence of the pathogen, water use was restricted at 15, 21, and 27 C but not at 33 C. Infection of avocado seedlings was related to soil temperature at a depth of 10 cm in an avocado grove in California, with maximum infection in the summer and fall months when soil temperatures reached maximum levels of 24.5 to 25.5 C. In July, August, and September, there were at least 570 hr/mo when the soil temperature was 20 C or over; in August and September, there were 30 and 36 hr, respectively, when soil temperature was over 25 C.