Population Dynamics and Diversity ofPseudomonas syringaeon Maple and Pear Trees and Associated Grasses

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Abstract
The number of epiphytic Pseudomonas syringae isolated from maple [Acer rubrum] twigs and leaves between July 1985 and September 1986 was erratic (undetectable to 105 cfu/g), whereas the number isolated from pear was more stable and often higher (103 to 106 cfu/g). P. syringae was isolated consistently (about 104-107 cfu/g) from perennial rye, orchard, red fescue, annual rye, and brome grasses growing trees in the maple nursery and from perennial rye grass in the pear orchard. In greenhouse pathogenicity test, 87% of the P. syringae isolates from maple trees was pathogenic in maple seedlings, whereas 15% of the isolates from pear trees was pathogenic in young pear trees. Of the isolates tested from grasses, 55% from the maple nursery was pathogenic in maple seedlings, and 29% from grass in the pear orchard was pathogenic in young pear trees. These data indicate that grasses and trees support reserviors of inoculum of pathogenic P. syringae. Indigenous isolates from a maple nursery were variable relative to pathogenicity and DNA restriction-fragment analysis, indicating that epiphytic populations of P. syringae from the grasses and trees were heterogenous.