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Bacterial Speck of Tomato: Sources of Inoculum and Establishment of a Resident Population. R. W. Schneider, Department of Plant Pathology, University of California, Davis 95616, Present address of senior author: Department of Plant Pathology, University of California, Berkeley 94720; R. G. Grogan, Department of Plant Pathology, University of California, Davis 95616. Phytopathology 67:388-394. Accepted for publication 10 September 1976. Copyright 1977 The American Phytopathological Society, 3340 Pilot Knob Road, St. Paul, MN 55121. All rights reserved.. DOI: 10.1094/Phyto-67-388.

Bacteria capable of inciting speck on tomato leaves were isolated from roots and foliage of diverse weed and crop plants in soils with and without a history of tomato culture. In greenhouse and field experiments, soil-borne inoculum incited foliar symptoms of the disease. Also, Pseudomonas tomato (P. syringae) was isolated from apparently symptomless leaves collected from commercial tomato fields. Resident populations of the bacterium persisted for long periods in association with tomato leaves, but were reduced to low levels at 32 C even when free moisture was maintained for 48 hr. A portion of the resident population survived under warm, dry conditions in the field for at least 14 days after inoculation, but did not cause obvious symptoms. However, after leaves were wet for 24 hr, symptoms developed within 3-5 days. Exposure of tomato seedlings to 39 C for 6 hr before inoculation increased susceptibility to invasion and/or infection by the bacterium.

Additional keywords: epidemiology, Lycopersicon esculentum.