Competition for nodule formation between introduced strains of Mesorhizobium ciceri and the native populations of rhizobia nodulating chickpea (Cicer arietinum) in Tunisia

Chickpea is the most cultivated grain iegume in the world and it shares the first rank with faba bean in Tunisia. However, the yield remains low, mainly due to the limited availability of N and P, and to the severe bioclimatic conditions. No inoculation trials had been conducted on chickpea in the Tunisian soils. This paper reports the yield response to inoculation by two different strains of Mesorhizobium ciceri, an exogenous type strain (UPMCa7(T)) and a selected local strain (CMG6). Field experiments were conducted in different sites in the north of Tunisia using three chickpea cultivars, (cvs. Amdoun I, Chetoui and Kasseb). Rhizobia occupying field nodules were isolated and identified using 16S rDNA typing for both inoculated and non-inoculated plots. In contrast to the exogenous strain, the local strain gave a significant increase in nodule number and shoot dry yield in all the experimental fields for the three cultivars used. Monitoring of the nodule occupancy showed that the local strain competed well the native populations of rhizobia. The usefulness and the persistence of this strain in the different soils where it was introduced will be assessed further during the next years.