THE USE OF GUS-REPORTER GENE TO STUDY THE EFFECT OF AZOSPIRILLUM-RHIZOBIUM COINOCULATION ON NODULATION OF WHITE CLOVER

The gusA-marked Azospirillum lipoferum T1371, constructed by inserting transposon mTn5SSgusA20 from Escherichia coli S17-1 lambda-pir into t he genome of Azospirillum lipoferum 137, was used to evaluate its effe ct on nodulation of white clover with and without Rhizobium inoculatio n. When inoculated alone, Azospirillum colonized the tap roots, second ary roots and root hairs. The combined inoculation of white clover wit h Rhizobium leguminosarum by trifolii and A. lipoferum enhanced the nu mber of nodules by 2-3 times from 5 to 20 days after inoculation (DAI) . The combined inoculation also enhanced acetylene reduction activity by 2.3-2.7 times at 20 DAI. Moreover, Azospirillum was observed coloni zing the tap root, root hairs and sites near or on the nodules. These results suggest that the formation of additional infection sites by A. lipoferum, with a combined inoculation, may be the mechanism that wil l enhance nodulation and nitrogen fixation of white clover.