POPULATION-DENSITY OF THE BIOCONTROL AGENT BURKHOLDERIA-CEPACIA AMMDR1 ON 4 PEA CULTIVARS

We determined if the biocontrol bacterial strain, Burkholderia cepacia AMMDR1, introduced as a seed treatment, persisted on pea roots, and h ow 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 popula tions differed among cultivars. Total culturable aerobic bacteria, ind igenous B. cepacia and introduced B. cepacia AMMDR1 were sampled from root segments of each cultivar grown from either treated or non-treate d seed at 1, 2, 4 and 6 wk after planting. The population density of t he 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 indigen ous B. cepacia only at 2 wk after planting. Introduction of the biocon trol agent, which comprised 1-10% of the total bacteria on each date, did not increase the total number of culturable aerobic bacteria on ro ot 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 res ults suggest that roots may have a Carrying capacity for bacteria in g eneral, and also for a specific functional group or species such as B. cepacia.