Longevity of Microbial Biocontrol Agents in a Planting Mix Amended with Glomus intraradices
Abstract:Commercial sources of the biological control agents Bacillus subtilis , Trichoderma harzianum and Streptomyces griseoviridis and experimental single isolates of Serratia plymuthica , a Pseudomonas fluorescens parent and its lacZY mutant were evaluated for their survival and compatibility with the mycorrhizal fungus, Glomus intraradices , in a commercial planting mix. The control treatments were the unamended mix and mix amended with G. intraradices alone. All were applied to 128-cell Speedling styrofoam flats and planted with the tomato cultivar 'Sunny'. At four to five intervals during the growing period (6.5-8 weeks), each organism was quantified by dilution plating and G. intraradices infection (%) was determined at the end of each test. The number of Trichoderma isolates increased slightly within 2 weeks after application and then stabilized through the end of the test. Serratia and Streptomyces isolates declined throughout the test from about 7.75 log colony-forming units (CFU) g - 1 to numbers at the end (6.2 log CFU g - 1) similar to the controls. Bacillus isolates declined about 1 log CFU g - 1 in the first week but then stabilized. G. intraradices had no influence on numbers of these four genera. The Pseudomonas parent and its lacZY mutant declined about 1 log CFU g - 1 during the test with the mutant yielding higher CFU for each sampling period. Propagules of both Pseudomonas isolates were greater when mixed with G. intraradices than when alone. In these experiments, Bacillus and Trichoderma were the best survivors in a mix for potential use as biocontrol agents for tomato transplants.
Document Type: Research Article
Publication date: 1997-06-01