Selection of rhizobacteria for the control of Pythium ultimum and Aphanomyces cochlioides on sugar-beet seedlings
1996
Williams, G.E. | Asher, M.J.C.
Approximately 400 bacterial isolates from the roots of field-grown sugar-beet seedlings were examined for their ability to inhibit the growth of Pythium ultimum and Aphanomyces cochlioides in culture and to suppress disease caused by these pathogens when applied to pelleted sugar-beet seed in artificially infested soil. Biocontrol potential was assessed in controlled environments, under optimal conditions for disease development and expression. A large proportion of the rhizobacteria isolates were antagonistic to the fungi in culture, but only c. 1% were effective biocontrol agents. Isolates that inhibited growth in vitro were, in general, active against both fungal species, whereas in vivo, isolates that most suppressed P. ultimum were different from those most effective against A. cochlioides. Over all isolates with both pathogens, there was no correlation between the degree of inhibition in culture and the extent of disease suppression. Effective biocontrol isolates significantly improved seedling emergence and the proportion of healthy seedlings compared with untreated seed. However, under the high disease pressure generated in these experiments, the level of protection fell short of that achieved with the fungicides currently in use on sugar-beet seed.
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