Population density of the biocontrol agent Burkholderia cepacia AMMDR1 on four pea cultivars

We determined if the biocontrol bacterial strain, Burkholderia cepacia AMMDR1, introduced as a seed treatment, persisted on pea roots, and how its presence affected populations of both indigenous B. cepacia and total culturable aerobic bacteria in the rhizosphere. The experiment was conducted with four pea cultivars to determine if bacterial populations differed among cultivars. Total culturable aerobic bacteria, indigenous B. cepacia and introduced B. cepacia AMMDR1 were sampled from root segments of each cultivar grown from either treated or non-treated seed at 1, 2, 4 and 6 wk after planting. The population density of the introduced strain did not differ significantly among cultivars, nor was there a significant cultivar effect on total bacteria at three of four sampling dates. Cultivars supported different numbers of indigenous B. cepacia only at 2 wk after planting. Introduction of the biocontrol agent, which comprised 1-10% of the total bacteria on each date, did not increase the total number of culturable aerobic bacteria on root segments in comparison to no treatment. The number of indigenous B. cepacia on roots grown from non-treated seeds was similar to that of the introduced strain by the end of the 6-wk growing season. These results suggest that roots may have a Carrying capacity for bacteria in general, and also for a specific functional group or species such as B. cepacia.