Responses of crimson clover to inoculation with genetically marked strains of rhizobium trifolii

Abstract

In order to increase the utilization of annual clovers in pastures, information is needed on seasonal Rhizobium trifolii‐crimson clover (Trifolium incarnatum L.) interactions relating to factors affecting dinitrogen fixation rates. Five double‐antibiotic labelled strains of R. trifolii were evaluated for symbiotic effectiveness when in competition with indigenous rhizobia in nodulating ‘Tibbee’ crimson clover. Experiments were conducted in two soil environments, an ultisol and a vertisol, over two consecutive growing seasons. Successful nodulation of crimson clover by the introduced strains varied significantly within and between locations over both growing seasons. Strain 162K10, though highly competitive at the ultisol location, was dominated by the indigenous rhizobia over both seasons at the vertisol site. Strain RP113–14 occupied more than 90% of the nodules during the first growing season although this declined to only 60% in the subsequent season at the ultisol site. On the vertisol site, the results with RP113–14 were reversed. Strain RP111–51 was the only strain to predominantly nodulate crimson clover over both seasons at both locations. Indigenous populations of R. trifolii at the vertisol site dominated strains 162K10, RP113–14, LM207, and TA1 throughout the establishment year, although 162K10 and RP113–14 survived for the following year and increased their nodule occupancies to 71 and 86%, respectively. A local isolate selection, LM207, and an ineffective mutant of strain TA1 were both over‐whelmed by the indigenous populations. Higher forage production and more robust clover stands were associated with the most competitive amended strains. It was apparent that crimson clover production can be enhanced by the introduction of more effective R. trifolii strains.

Key words:

• Nitrogen‐fixation
• Forage Legumes
• Microbial Ecology

Notes

Research supported by the Science and Education Administration of the U. S. Department of Agriculture under Grant No. 5901–0410–8–0051–0 from the Cooperative Grants Research Office. Contribution from the Department of Agronomy, Mississippi State Univ., and the Mississippi Agric. and Forestry Exp. Stn. Approved by the Director as Technical Paper No. 5274.

Research Associate and Associate Professor, respectively, Department of Agronomy, P. 0. Box 5248, Mississippi State, MS 39762.