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Seasonal Development of Armillaria Root Rot of Peach as Influenced by Fungal Isolates. W. Wilbur, Staff Research Associate IV, Department of Plant Pathology, University of California, Riverside 92502; Donald E. Munnecke(2), and Ellis F. Darley(3). (2)(3)Professor and Plant Pathologist, Department of Plant Pathology, University of California, Riverside 92502. Phytopathology 62:567-570. Accepted for publication 28 December 1971. DOI: 10.1094/Phyto-62-567.

Four clones of Armillaria mellea isolated from plants in areas of California remote from one another were tested for pathogenicity on peach trees in the field at Riverside. Infection of trees from inoculum produced on fig or citrus wood was comparable. One year after inoculation; over 60% of the trees were killed by clone D-9; ca. 25% were killed by clones D-2 and D-86; and only 5% were killed by clone D-73. By the end of 3 years, the per cent killed was 100, 86, 71, and 60 for trees inoculated with clones D-9, D-2, D-86 and D-73, respectively. In 3 years, 86% of the 168 inoculated trees were dead. The per cent of those killed during the four seasons was approximately as follows: winter, 2; spring, 23; summer, 66; and fall, 10. After 3 years, infection had spread to 56 noninoculated trees as follows: dead, 14%; severely infected, 7%; moderately or slightly infected, 71%; and none visibly infected, 8%.

Additional keywords: California clones of Armillaria, pathogenicity of Armillaria, spread of Armillaria.