ISHS Acta Horticulturae 338: VI International Workshop on Fireblight
PROTECTION AGAINST FIRE BLIGHT BY AVIRULENT STRAINS OF ERWINIA AMYLOVORA: MODULATION OF THE INTERACTION BY AVIRULENT MUTANTS |
| Authors: | M. Tharaud, E. Baudouin, J.P. Paulin |
| Abstract:
Previous results showed that high levels of protection (90–95%) against Fire Blight could be achieved when a naturally avirulent strain of the pathogen Erwinia amylovora was applied before the virulent strain, in suitable conditions. In this study we used 18 well characterized insertion avirulent mutants of E. amylovora to analyse the role played by the avirulent strain in the interaction. Young apple seedlings were inoculated with avirulent and virulent strains, after wounding of the youngest unfolded leaf. Two types of inoculation were used: "sequenced inoculation" (the avirulent strain was applied 2h before the virulent one) and "co-inoculation" (the two strains were mixed, then immediatly applied on the wound). Inoculum concentrations of avirulent and virulent strains were 3.107 and 3.106 cfu/leaf, respectively. With sequenced inoculation, most of the tested mutants were able to protect apple seedlings. Population dynamics studies showed that in such conditions, hatever the inducer, the population of the virulent strain decreased to a very low level. In contrast, with co-inoculation only 2 avirulent strains were able to confer a high level of protection: a naturally avirulent strain and one hrp- insertion mutant; in these conditions population of the virulent strain decreased. When there is no protection the virulent strain multiplied after a delay, as compared with the control. These results indicate that the interaction between host plant/virulent strain/avirulent strain leading to a protective or a non protective situation might be modulated by the avirulent strain itself. | |
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