Zoospore Homing and Infection Events: Effects of the Biocontrol Bacterium Burkholderia cepacia AMMDR1 on Two Oomycete Pathogens of Pea (Pisum sativum L.)

摘要

Burkholderia cepacia AMMDR1 is a biocontrol agent that protects pea and sweet corn seeds from Pythium damping-off in field experiments. The goal of this work was to understand the effect ofB. cepacia AMMDR1 on Pythium aphanidermatum andAphanomyces euteiches zoospore homing events and on infection of pea seeds or roots. In vitro, B. cepaciaAMMDR1 caused zoospore lysis, prevented cyst germination, and inhibited germ tube growth of both oomycetes. B. cepacia AMMDR1 also reduced the attractiveness of seed exudates to Pythiumzoospores to nondetectable levels. However, when present at high levels on seeds, B. cepacia AMMDR1 had little net effect on zoospore attraction, probably because it also enhanced seed exudation. Seed-applied B. cepacia AMMDR1 dramatically reduced the incidence of infection by Pythium zoospores in situ compared with an antibiosis-deficient Tn5 mutant strain. This mutant strain also decreased Pythium infection incidence to some extent, but only when the pathogen inoculum potential was low. B. cepacia AMMDR1 did not affect attraction ofAphanomyces zoospores or Aphanomyces root rot incidence. These results suggest that B. cepacia AMMDR1 controlsP. aphanidermatum largely through antibiosis, but competition for zoospore-attracting compounds can contribute to the effect. Differences in suppression of Aphanomyces andPythium are discussed in relation to differences in the ecology of the two pathogens.