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Abstract
Seven avirulent strains of Erwinia amylovora were mixed in various combinations and tested for virulence. Only one combination, where the capsulated avirulent strain P66 was combined with the non-capsulated avirulent strain 4S2, induced fireblight symptoms in immature pear fruits and apple shoots. Growth studies in vivo strongly suggested that these strains were acting synergistically and that the non-capsulated strain possessed another, as yet unknown, virulence factor.
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© Society for General Microbiology 1980