ASSESSMENT OF COMPETITIVENESS OF RHIZOBIA INFECTING GALEGA-ORIENTALISON THE BASIS OF PLANT-YIELD, NODULATION, AND STRAIN IDENTIFICATION BYANTIBIOTIC-RESISTANCE AND PCR

Competition between effective and ineffective Rhizobium galegae strain s nodulating Galega orientalis was examined on the basis of plant grow th, nodulation, antibiotic resistance, and PCR results, In a prelimina ry experiment in Leonard's jars, ineffective R. galegae strains HAMBI 1207 and HAMBI 1209 competed in similar manners with the effective str ain R. galegae HAMBI 1174, In a pot experiment, soil was inoculated wi th 0 to 10(5) HAMBI 1207 cells per g before G. orientalis was sown, Se eds of G. orientalis were surface inoculated with 2 x 10(4) and 2 x 10 (5) cells of HAMBI 1174 per seed (which represent half and fivefold th e commercially recommended amount of inoculant, respectively). Plant y ield and nodulation by the effective strain were significantly reduced , with as few as 10(2) ineffective rhizobia per g of soil, and the ino culation response was not improved by the 10-fold greater dose of the inoculant, Bacteria occupying the nodules were identified by antibioti c resistance and PCR with primers specific for R, galegae HAMBI 1174, R, galegae, and genes coding for bacterial 16S rRNA (bacterial 16S rDN A). Sixty-two large nodules examined were occupied by the effective st rain HAMBI 1174, as proven by antibiotic resistance and amplification of the strain-specific fragment, From 20 small nodules, only the speci es-specific fragment could be amplified, and isolated bacteria had the same antibiotic resistance and 16S PCR restriction pattern as strain HAMBI 1207, PCR with our strain-specific and species-specific primers provides a powerful tool for strain identification of R. galegae direc tly from nodules without genetic modification of the bacteria.