Evaluation of Pea (Pisum sativum L) Rhizosphere Bacteria As Biocontrol Agents of Aphanomyces Root Rot.

Aphanomyces root rot, also called common root rot of legumes, is caused by Aphanomyces euteiches. Among the leguminous plant species field pea is the most notably affected crop. A. euteiches is becoming a problem in terms of sustainability of field pea production in Western Canada, and pea production is now under serious threat from this pathogen. Zoospore and mycelia are the pathogen infective stages primarily responsible for the development of water-soaked, honey-coloured lesions on the root, cortex and epicotyl that result in stunting, yellowing and wilting leaves, and often death of the entire plant. Until the recent introduction of the fungicide INTEGO^TM Solo (ethaboxam) as emergency use for the suppression of A. euteiches in field pea there were no effective control methods available in Canada. As a result, disease avoidance and crop rotation practices were the only available control measures. Therefore, the search for other effective control measures is needed. One such alternative is the development of microbial inoculants that can control or reduce the severity of the disease. Development of biological control agents must consider host-pathogen-environment interactions (i.e., plant/A. euteiches/rhizosphere). Such considerations enable the isolation of potential microorganisms which are naturally present in, and apparently adapted to, the pea rhizosphere. This research project comprises both in vitro and in vivo assays to evaluate pea rhizosphere bacteria as bacterial inoculants against A. euteiches. To date, screening of 170 rhizosphere bacteria identified 15 that inhibited Aphanomyces mycelial growth and, of these, seven inhibited zoospore germination on lab media. The efficacy of these seven isolates as soil inoculants in pot experiments is under evaluation.