Copper Resistance inPseudomonas syringaepv.syringaefrom Cherry Orchards and its Associated Transfer in Vitro and in Planta with a Plasmid

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Abstract
Copper-resistant Pseudomonas syrinage pv. syringae was recovered from blossoms of sweet and sour cherry from nine and 12 orchards in Michigan in 1987 and 1988, respectively. Isolates that did not grow on low nutrient CYE-glycerol medium amended with 40-120 .mu.g of cupric sulfate per milliliter were considered sensitive. Isolates that grew on media amended with 160-240 .mu.g of cupric sulfate per milliliter were considered to have low resistance and those that grew on media amended with 280-320 .mu.g of cupric sulfate per milliliter were considered to have high resistance. Among 17 copper-resistant isolates collected in 1987, 14 with high resistance contained a single plasmid of 46-73 kilobase pairs (kb) and three with low resistance lacked a detectable plasmid. A 61-kb plasmid was present in all 29 copper-resistant isolates selected in 1988 on media containing 200 .mu.g of cupric sulfate per milliliter. Among 15 copper-sensitive isolates, only one contained a plasmid. Copper resistance and a 61-kb plasmid were transferred in filter matings in three copper-sensitive recipient strains of P. s. syringae from each of six copper-resistant donor strains. A resulting exconjugant was successfully used as a donor strain in matings with two recipient strains. Copper resistance also was transferred when suspensions of donor and recipient strains were infiltrated into bean leaves. Populations of copper-sensitive strains of P. s. syringae were reduced significantly more than population of copper-resistant strains on bean leaves sprayed with cupric hydroxide. All P. s. morsprunorum detected in blossom samples was copper sensitive, and copper resistance was not transferred from P. s. syringae in filter matings to P. s. morsprunotum.