Biological control of Aphanomyces euteiches root-rot of pea with spore-forming bacteria

Spore-forming bacteria from New Zealand soils were evaluated for the biological control of pea root rot caused by Aphanomyces euteiches. In dual-culture assays, 31 of 704 bacterial isolates completely suppressed mycelial growth of the pathogen. Seven isolates (strains of Bacillus and Paenibacillus), that suppressed zoospore germination and germ-tube growth and five other bacterial isolates previously characterised as suppressive to A. euteiches, were tested in a glasshouse assay for disease suppression. One isolate each of B. pumilus, B. subtilis, B. cereus, B. mycoides and two isolates of P. polymyxa, reduced root rot and oospore formation within pea tissue, and were selected for further assessment. B. mycoides MW27 reduced oospore formation in pea roots by 83% (P < 0.05). In a field experiment, each of the six bacterial isolates reduced root rot, but not at statistically significant levels. The results were confounded by a high incidence of other root rotting fungi, particularly pathogenic Fusarium spp. A second field site with a disease complex predominantly based on A. euteiches was selected for a subsequent trial. In this case, prill, granule and seed coat formulations of Bacillus mycoides M W27 were tested. The seed coat formulation increased plot stand (P < 0.05) by approximately 9%, whilst the prill formulation increased yields per plot (P < 0.05) by approximately 17%.