Articles
BIOLOGICAL CONTROL OF FIRE BLIGHT
Strains of Erwinia herbicola and bacteriocins produced by them that inhibit E. amylovora, in vitro, have been evaluated for their influence on the incidence of fire blight infection.
Test preparations (suspensions of viable bacteria or cell-free bacteriocin preparations) were applied to apple blossoms in a research orchard both before and after inoculation with E. amylovora.
In 1979, two strains of E. herbicola provided significant control of infection when applied at 106 and 108 colony forming units (cfu) per milliliter.
With the higher concentration, control was equivalent to that achieved with 100 mg/l of streptomycin.
One of the strains tested produces, in vitro, a bacteriocin (MW.~800) that inhibits E. amy lovora; the other strain does not produce a bacteriocin.
However, both strains provided equivalent control.
Cell-free culture supernatents containing bacteriocin also significantly reduced the incidence of infection; a comparable preparation from a nonbacteriocinogenic strain did not affect disease incidence.
In 1980 however, partially purified bacteriocins from E. herbicola has little effect on disease development.
In 1980, a bacteriocinogenic strain of E. herbicola and a mitomycin C-induced nonbacteriocinogenic mutant of it were evaluated.
Both strains (applied at 108 cfu/ml) significantly reduced the incidence of infection, but not to the same extent as 100 mg/l of streptomycin.
Furthermore, when blossoms, which were treated with the bacteriocinogenic strain of E. herbicola, were inoculated with two strains of E. amy lovora, one that was sensitive to and one that was resistant to the bacteriocin in vitro, disease control was equivalent.
Application of E. herbicola at 1010 cfu/ml reduced disease incidence to the same extent (statistically) as application of streptomycin at 100 mg/l.
These data indicate that the incidence of fire blight can be reduced by treating apple blossoms with nonpathogenic bacteria and that disease control derives from mechanisms other than bacteriocinogenicity.