Publication no. D-1999-0602-01R

Lethal Cankers Caused by Phytophthora spp. in Almond Scions: Specific Etiology and Potential Inoculum Sources. G. T. Browne, USDA-ARS, Department of Plant Pathology, University of California, Davis 95616; M. A. Viveros, University of California Cooperative Extension, 1031 South Mt. Vernon Ave., Bakersfield 93307. Plant Dis. 83:739-745. Accepted for publication 1 April 1999. This article is in the public domain and not copyrightable. It may be freely reprinted with customary crediting of the source. The American Phytopathological Society, 1999.

Etiology of a new lethal canker syndrome of almond trees was investigated in the San Joaquin Valley of California. Phytophthora citricola was isolated most frequently from cankers limited to the aboveground scion portions of trees; whereas P. cactorum usually was isolated from cankers originating at or below the soil surface. Repeated observations and isolations indicated that some of the cankers associated with each species were perennial. In pathogenicity tests, isolates of P. cactorum and P. citricola caused bark cankers in excised segments of almond shoots and branches, as well as root and crown rot on potted almond seedlings. Only P. citricola caused significant disease in root and crown tissues of peach seedlings. When pear fruits and almond seedlings were used as bait, P. cactorum and P. citricola were isolated from orchard soil, debris collected in natural depressions where scaffold branches and the tree trunk joined at a common point, and debris deposited on tree surfaces during nut harvest. Control strategies for Phytophthora diseases of almond should consider aboveground as well as belowground modes of attack by P. citricola and P. cactorum. Debris infested with these pathogens and deposited on trees during harvest may play a role in the disease epidemiology. Additional keywords: Prunus dulcis.