Plant Growth-Promoting Rhizobacteria on Canola (Rapeseed)

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Abstract
During 1983 and 1984, more than 4,000 bacterial strains were collected in Canada from root zones of plants in diverse habitats. Strains were screened individually for Gram-stain reaction, growth at 4-14 C, metabolism of canola (rapeseed, Brassica campestris L. and B. napus L.) seed exudates, chemotaxis toward asparagine, and root colonization capacity. A total of 887 strains were tested in greenhouse assays for plant growth-promoting activity on canola. A marked increase in leaf are compared with the controls occurred with 222 strains in initial tests, and 35 strains enhanced growth in at least two of three repeating tests. Strains of plant growth-promoting rhizobacteria (PGPR) included Pseudomonas putida, P. putida biovar B, P. fluorescens, Arthrobacter citreus, and Serratia liquefaciens. Maximum yield promotion associated with PGPR in field trials in both 1985 and 1986 occurred when seeds were treated with bacterial suspensions; certain types of potential cell carriers produced some negative effects on plants. Plants treated with 13 of 28 strains of PGPR yielded up to 57% greater than the controls in individual trials with cell suspension inoculants in 1985. Three strains increased yields over a 2-yr period by 6 and 13% compared with the controls. Select PGPR strains also increased seedling emergence and vigor under field conditions.