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Latent Infections and Seasonal Variability of Crown Gall Development in Seedlings of Three Prunus species. Larry W. Moore, Assistant Professor of Plant Pathology, Department of Botany and Plant Pathology, Oregon State University, Corvallis 97331; Phytopathology 66:1097-1101. Accepted for publication 23 March 1976. Copyright © 1976 The American Phytopathological Society, 3340 Pilot Knob Road, St. Paul, MN 55121. All rights reserved.. DOI: 10.1094/Phyto-66-1097.

Infection by Agrobacterium tumefaciens and subsequent symptom expression was similar on seedlings of three Prunus species (mahaleb and mazzard cherries and myrobalan plum) that were wounded and inoculated in the field. They were heavily infected when inoculated in June, July, and August, but earlier and later inoculations were less successful. Soil moisture had little influence on symptom expression, but low soil temperature was correlated with reduced susceptibility. Latent infections occurred the first growing season on mahaleb and mazzard cherry seedlings wounded and inoculated after September and galls developed on these plants during the second growing season. Wounds were necessary for optimum infection of all three Prunus species, but many nonwounded 3-year-old mazzard trees became infected when inoculated during the growing season. Wounds on stored, dormant mazzard seedlings remained susceptible to A. tumefaciens for 107 days, whereas less than 20% of the wounds made in late June on mazzard seedlings growing in the field became infected when inoculated 6 days later. The extended period of wound susceptibility on dormant seedlings and latent infections must be carefully considered in devising methods to prevent crown gall.