VIEW ARTICLE

Influence of Inoculum Dosage, Time After Wounding, and Season on Infection of Persian Walnut Trees by Erwinia rubrifaciens. N. W. Schaad, Department of Plant Pathology, University of California, Davis 95616, Present address: Department of Plant Pathology, University of Georgia, Experiment 30212; M. G. Heskett(2), J. M. Gardner(3), and C. I. Kado(4). (2)(3)(4)Department of Plant Pathology, University of California, Davis 95616. Phytopathology 63:327-329. Accepted for publication 19 September 1972. DOI: 10.1094/Phyto-63-327.

Experimentally inflicted wounds of Persian walnuts (Juglans regia ‘Hartley’) are susceptible to infection by Erwinia rubrifaciens. Susceptibility depends on season of the year; time of adding inoculum to the open wound; and the amount of the inoculum. Hartley trees were not susceptible during the winter (January), but were highly susceptible in spring (April), summer (July), and fall (October) months. No infection occurred in January even at high levels of inoculum (graded inoculum doses up to 10⁶ cells/ml were used). Very few E. rubrifaciens cells (5-10 cells/wound) were needed to establish infection in April, July, and October. Wounds decreased in susceptibility with time at the average rate of 10-12%/day. Seven days after wounding, fewer than 3% of wounds remained susceptible in April and October, and about 15% in July. The implications of these results are discussed.