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Disease Note.

First Report of Phytophthora caclorum Causing Root and Collar Rot of Apple in Northeastern Spain. K. A. Jacobs, U.S. National Arboretum, Washington, DC 20002. S. Verdejo-Lucas, Dpto. Patologia Vegetal, IRTA, 08348 Cabrils, Spain, and J. Carb6, Fundaci6 Mas Badia, 17134 La Tallada, Spain. Plant Dis. 78:529. Accepted for publication 16 November 1993. Copyright 1994 The American Phytopathological Society. DOI: 10.1094/PD-78-0529E.

Apples (Malus domestica Borkh.) are grown on approximately 60,000 ha. in Catalonia (northeastern Spain). Symptoms of rapid leaf drop, branch death, and collar and root necrosis were observed on a few trees in an orchard in 1991. The trees were propagated on MM. 106 rootstock, which is known to be highly susceptible lo Phytophthora root and crown diseases. Samples of soil, rool, and crown tissue were taken from two trees showing symptoms and from an adjacent, asymptomatic tree in February 1992. Phytophthora caclorum (Lebert & Colin) Schroter was isolated from the asymptomatic tree and surrounding soil. The fungus was identified on the basis of colony and hyphal morphology and characteristics of the sporangia, and its identification was confirmed by J. M. Mircetich, University of California, Davis. In order to determine if P. caclorum was present on other asymptomatic trees and dispersed throughout the orchard, soil and root samples were subsequently collected from 32 trees on MM. 106 rootstock. Roots were washed and plated onto PARP semiselective medium (1), and soils were baited with immature carnation petals. Phytophthora caclorum was recovered from the soil and roots of three trees located in depressions where standing water was common. Two of the trees that were positive for P. caclorum exhibited aerial symptoms as described above at the time of sampling, and by July 1993, one of the three trees had died. The third tree that was positive for P. caclorum did not show symptoms al the time of sampling but developed them by July 1993. This is the first report of P. caclorum causing root and crown rot of apple in Spain, and its presence should be considered in the selection of rootstocks, soil treatments, and cultural practices in apple orchards.

Reference: (1) M. E. Kannwisher and D. J. Mitchell. Phytopathology 68:1760, 1978.