SUMMARY: Phage types representative of the population of indigenous at each of two sites were evaluated for plasmid content by agarose gel electrophoresis and for symbiotic effectiveness with cv. Saranac. Relative to four strains used commercially, 55 and 65 phage types representing these populations showed a high average level of symbiotic effectiveness; only a single type from one site was relatively ineffective in symbiosis. On the basis of plasmid number and molecular mass, 160 isolates comprising 45 and 48 types from both sites were placed in 22 different groups with 17 and 13 groups from the respective sites. The number of plasmids varied between one and five per isolate with molecular masses ranging from 5 MDa to considerably greater than 267 MDa. Only five isolates lacked a plasmid with mobility in agarose gels corresponding to that of a reference megaplasmid but instead showed a band of lesser mobility and therefore greater molecular mass. Phage types, which were divided into plasmid groups solely on the basis of differences between isolates from each site, may reflect adaptation of to their respective sites. Differences between isolates within certain phage types due to the presence or absence of a single plasmid may have resulted from genetic interchange between indigenous There was no significant correlation between plasmid number or mass and symbiotic effectiveness or phage sensitivity of the phage types from either site.


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