Abstract:
A pot experiment was conducted to test the efficiencyof two Rhizobium strains; in fixing atmospheric nitrogen one strain from Sudan: (ENRRI16a) ,isolated from central Sudan, and a commercial strain, ICRISAT 7001 isolated from India on three Sudanese groundnut cultivars, selected in Sudan as high yielders; Ahmedy, Tozy and Bunting.
The tested Rhizobium strains on the groundnut cultivars used did not supply the cultivars with the needed nitrogen for optimum growth as evidenced by the finding that mineral fertilizer added as urea consistently outyielded all the Rhizobium strains added as inoculums in shoot weight followed by strain ENRRI16a when applied at a high inoculums dose (4×106 CFU /ml).
The cultivars tested, however, interacted differently with the Rhizobium strains depending on the inoculums dose, and to mineral nitrogen added as urea. The Bunting cultivar was very responsive to mineral nitrogen addition. Ahmedy cultivar did not form any nodules with the local strain from Sudan when added at two different doses which indicated incompatibility between the Rhizobium strain and some of the tested cultivars. The local strain formed nodules with the other two cultivars with a noticed trend of higher infectivity and efficiency with the Bunting cultivar. Similar trend was reported with the nodule dry mass. This confirmed the significance of the right selection of the right cultivar for the right Rhizobium
The cultivars responded differently to inoculums doses. In response to the addition of high inoculums dose, strain ENRRI16a, however when applied at a lower dose significantly out yielded the control with Tozy and Bunting cultivars, while giving a lower shoot weight with Ahmedy cultivar. The performance of the other Rhizobium strain; ICRISAT7001 at the high dose of inoculum was comparable with mineral nitrogen addition as well as with the ENRRI16a strain. Similar trend was noticed with the root dry weight.
These findings were not reflected in plant tissue nitrogen content, which may be attributed to the short duration of the experiment.
It is clear from this study that both added Rhizobium strains were not able to supply the groundnut cultivars with the required nitrogen for optimum growth, despite their variability in performance.
Further research is stressed I the future to mark the added Rhizobium strains, whether local or exotic to determine nodules occupancy and correlate it with the measured nitrogen fixation traits to offer further help in recommending the suitable Rhizobium strain to be used with the optimum inoculums dose and with the compatible groundnut cultivar.
