Testing the Impact of USDA Rhizobia Accessions on Nodulation, Nitrogen Assimilation, and Productivity of Guar.

Legume inoculants are products that introduce legume-specific Rhizobia bacteria to the soil and promote the process of biological nitrogen fixation. Guar (Cyamopsis tetragonolobus L.) is a legume produced in semi-arid regions around the world, primarily for industrial uses of guar gum; but, there is no known commercial inoculant products for the crop. However, the USDA National Rhizobium Germplasm Collection has four strains listed as compatible with guar: USDA 3089, USDA 3385, USDA 3386, and USDA 3595. The objective of this research is to test the efficacy of four peat-based inoculants derived from these strains, as well as a mixture and a non-inoculated control, in two sets of studies. The first study was conducted in pots in a greenhouse in Locket, TX. Using two soils as treatments, two substrates that differ biologically and physically were provided to test the six inoculant treatments. 50 days after planting, the pots were deconstructed to quantify treatment effects on nodulation, nitrogen assimilation, and productivity of guar relative to the untreated control. Simultaneously, a large pot study occurred at two locations: Locket, TX and Chillicothe, TX. The pots contained soil from their respective locations and guar plants were grown and monitored until maturity. Nitrogen assimilation, growth, and yield were evaluated. Any beneficial Rhizobia strains identified in these studies will be recommended for further testing in the field in order to develop an effective inoculant for guar.