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Effects of Low Temperature on Resistance of Almond Trees to Phytophthora Pruning Wound Cankers in Relation to Lignin and Suberin Formation in Wounded Bark Tissue. M. A. Doster, Graduate research assistant, Department of Plant Pathology, University of California, Davis 95616; R. M. Bostock, Associate professor, Department of Plant Pathology, University of California, Davis 95616. Phytopathology 78:478-483. Accepted for publication 21 October 1987. Copyright 1988 The American Phytopathological Society. DOI: 10.1094/Phyto-78-478.

As the temperature was lowered at which bark wounds were aged, the development of resistance to bark cankers caused by Phytophthora syringae was slowed. All fresh wounds inoculated with P. syringae resulted in cankers. In stem wounds aged for 2 wk at 25 C before inoculation, only 38% of the inoculated wounds developed cankers, while when aged at 6 C, all of the inoculated wounds developed cankers. In orchard trees throughout the fall and winter, inoculation with P. syringae resulted in cankers in all of the fresh wounds, most of the 2-wk-old wounds, and many of the 4-wk-old wounds, but almost all inoculated 6-wk-old wounds were immune to infection. As temperature was decreased, less lignin and suberin were observed histochemically and less ligninthioglycolic acid (LTGA) was detected in almond bark wounds using the thioglycolic acid assay. There was almost a threefold increase in LTGA in 2-wk-old wounds when aged at 25 C than when aged at 6 C. During winter, the resistance to infection by P. syringae of 2- and 4-wk-old wounds did not consistently correspond to the mean temperature for the period of wound aging, suggesting that other factors in addition to temperature are involved in resistance development.