ISHS Acta Horticulturae 273: V International Workshop on Fireblight
CONTROL OF FIRE BLIGHT BY ERWINIA HERBICOLA Eh252 : ROLE OF ANTIBIOTIC PRODUCTION |
| Authors: | J.L. Vanneste, L.B. Smart, C.H. Zumoff, J. Yu, S.V. Beer |
| Abstract:
Strains of E. herbicola, a non pathogenic epiphytic bacterium, that are particularly effective in controlling fire blight, have been found to inhibit in vitro the growth of E. amylovora by an antibiotic-based mechanism (Wodzinski et al. 1987). To evaluate the role of the antibiotic produced by E. herbicola strain Eh252 in the control of fire blight, two approaches were taken. In the first approach, we compared the percentage of infection of immature pear fruits treated with Eh252 and then inoculated with either the wild type strain of E. amylovora Ea273, or a derivative of Ea273 which is resistant to the antibiotic produced by E. herbicola Eh252. In the second approach, we compared the percentage of infection of immature pear fruit treated, prior to inoculation with Ea273, with either Eh252 or with mutants of Eh252 that lack antibiotic production. In the first set of experiments, immature pear fruits were treated with a suspension of Eh252 (106 cfu/fruit or 107 cfu/fruit) and then inoculated with E. amylovora (2 x 106 cfu/fruit) Ea273 or Ea273R a derivative selected on Petri-dish for its resistance to the antibiotic produced by Eh252. The fruits were incubated at 27°C in a moist chamber and scored daily for infection (presence of bacterial exudate in and around the well). When buffer was used instead of E. herbicola, 100% of the fruits were infected after 3 days of incubation. Pear fruits treated with Eh 252, showed reduced infection from Ea273 or Ea273R; this reduction of infection was greater when higher populations of E. herbicola were used. However, disease induced by the strain Ea 273R was always much greater than that induced by the wild-type strain. These data suggest that antibiotic production is involved in inhibition of E. amylovora in pear tissue, but that other mechanisms also are involved. For the second set of experiments, we first isolated isogenic mutants of Eh252 deficient in antibiotic production. A derivative of the bacteriophage lambda (b 221, Oam29, Pam80, rex::Tn5 132, cI857) was used as vector for the transposon Tn5 (De Bruijn and Lupski, 1984). Because Eh252 is not sensitive to lambda, the plasmid pTROY9 (De Vries et al, 1984), which contains and expresses constitutively the lamB gene of Escherichia coli, was introduced into Eh252. Strain Eh252(pTROY9) was transfected with the lambda derivative containing Tn5. Of 1500 kanamycin-resistant | |
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