First Report of Avocado Fruit Rot Caused by Phytophthora citricola in California. S. T. Koike, Office of Agricultural Commissioner, Santa Barbara County, CA 93110. D. G. Ouimette, and M. D. Coffey. Department of Plant Pathology, University of California, Riverside 92521. Plant Dis. 71:1045. Accepted for publication 14 August 1987. Copyright 1987 The American Phytopathological Society. DOI: 10.1094/PD-71-1045E.
Mature, unripe avocado fruit (Persea americana Mill. 'Hass') located
on the lower branches of trees in a grove in northern Santa Barbara
County showed fruit rot symptoms consisting of dark, circular lesions
up to 8 cm in diameter externally and a firm, brown rot internally.
Symptoms were observed during the early spring in 1986 and 1987 after
heavy rains. A single species of Phytophthora was consistently isolated
from the peel, flesh of the fruit, and pedicel using a Phytophthora selective
medium (1). The fungus was identified as P. citricola Sawada
and was morphologically indistinguishable from other isolates of the
same species previously described on avocado as the cause of a crown or
collar rot (2). In this same grove, P. citricola was also isolated from soil,
avocado feeder roots, and trunk cankers. In laboratory tests, 1 X 105
zoospores inoculated without wounding onto unripe, mature fruit
infected the peel within 16 hr at 24 C and caused extensive rot after 5
days at 24 C but not at 18 C.