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Effect of Soil pH on Susceptibility of Peach to Pseudomonas syringae. D. J. Weaver, Research Plant Pathologist, Agricultural Research Service, U.S. Department of Agriculture, Southeastern Fruit and Tree Nut Research Station, P.O. Box 87, Byron, Georgia 31008; E. J. Wehunt, Research Plant Pathologist, Agricultural Research Service, U.S. Department of Agriculture, Southeastern Fruit and Tree Nut Research Station, P.O. Box 87, Byron, Georgia 31008. Phytopathology 65:984-989. Accepted for publication 31 March 1975. DOI: 10.1094/Phyto-65-984.

‘Elberta’ peach seedlings were grown in pots of soil from a peach orchard where bacterial canker had occurred, and were artifically inoculated with Pseudomonas syringae after they had become dormant. Seven weeks later, three of five of the inoculated trees in unadjusted soil (pH 5.6) had died. Two of five plants in soil adjusted to pH 6.1 with MgCO₃ also died, but no plants died in soil adjusted to pH 6.4, 6.6, 6.9, or 7.2 with CaCO₃ or MgCO₃. No differences in stem length, fresh weight of roots, or discoloration of feeder roots were observed among the treatments. However, percentage of dry matter in roots was greater for plants grown at pH 6.4-6.9 than at 5.6, 6.1, or 7.2. Vesicular-arbuscular mycorrhizae were present in 77 to 94% of the feeder roots, with fewest roots infected at pH 6.6 where MgCO₃ was used. Numbers of propagules of Pythium spp. in soil, and recovery from roots were positively correlated with soil pH. In December, populations of Criconemoides xenoplax was greater in soil adjusted above pH 6.1, but differences were not significant in March and April.