Soybean Glycine Max L Merill Promiscuity Reaction To Indigenous Bradyrhizobia inoculation In Some Ghanaian Soils

ABSTRACT For many tropical countries particularly in Africa Biological Nitrogen Fixation BNF continues to be the most promising alternative or supplement to the use of chemical Nitrogen fertilizers for sustainable Agriculture. In contrast to cowpea that nodulate profusely in tropical soilswith the naturally occurring bradyrhizobia nodulation and nitrogen fixation in the American-type soybean in similar environments has largely depended on inoculating bradyrhizobia into the soil. The development of the Tropical Glycine Cross TGx soybean varieties by IITA has made it possible for these promiscuous varieties to nodulate with the naturally occurring strains belonging to the cowpea Bradyrhizobiumspp. The Most Probable Number MPN technique was used to determine the bradyrhizobial population in these soils. Eighty four Bradyrhizobium isolates obtained from randomly selected nodules on soybean were assessed for effectiveness in nitrogen fixation. Three of the most effective isolates were used in inoculation studies carried out in the greenhouse atthe University of Ghana-Legonon three promiscuous soybean varieties Anidaso TGx 813-6D TGx 1903-8F and TGx 1448-2E and a non- promiscuous genotype Davis in three Ghanaian soil series Toje Chromic cambisols Chichiwere Dystricfluvisol and Bekwai Ferric acrisols. There were tremendous inoculation responses in these soils for both the promiscuous and non-promiscuous cultivars with even the promiscuous ones responding better to inoculation than the non-promiscuous Davis. Inoculation gave rise to significant increases in nodule number nodule dry weight shoot dry weight and total nitrogen accumulation compared to the uninoculated control even intheChichiwere soil series which harboured the highestpopulation of indigenous bradyrhizobia suggesting that the populations of the naturally occurring bradyrhizobia in these soils were either not highly competitive or sufficient for optimum nodulation and nitrogen fixation. For all the symbiotic or growth parameters assessed the four soybean varietieswere ranked as DavisTGx1448-2ETGx1903-8FAnidaso TGx 813-6D.