ABSTRACT

Laboratory and screenhouse experiments were conducted to isolate and characterize rhizobia from soils collected from the northern Guinea, southern Guinea and Sudan savannas of Nigeria and to assess response of promiscuous soybean, TGx1448-2E to inoculation in the same soils. Bulk top soils were collected from 45 sites spread in 15 local government areas of Kaduna and Kano states. The treatments used in the screenhouse pot experiment were uninoculated control, mineral nitrogen and Legumefix, a commercial rhizobia inoculant. The treatments were arranged in Randomized Complete Block Design (RCBD) and replicated three times. Nodulation and biomass were assessed at eight weeks after planting. Response to inoculation and relative efficiency were also calculated. Nodule number and fresh weight were higher in inoculated plants than those treated with mineral nitrogen (N) across all the agro-ecological zones (AEZs). Generally, mineral N gave the highest dry matter yield (DMY) than the uninoculated control. Only about 40% of inoculated plants had DMY similar to mineral N while the remaining fall within the same range as the control. The disparity between mineral N and the other treatments provides opportunity to evaluate more rhizobia strains or inoculants that can improve the performance of soybean in the study sites. The results showed that response to inoculation was higher in the Sudan savanna than in the northern Guinea savanna. These were observed in 12 out of 21 and 9 out of 19 sites in the Sudan savanna and northern Guinea savanna respectively. Of these, inoculation response reached 62 and 90% in two sites only in the Sudan savanna while it barely reached 20% in the remaining sites. The results also showed a relative efficiency of greater than 100% in some locations which implies that the indigenous rhizobia populations were superior to mineral N and Legumefix inoculant. Notable among the locations were Albasu 1, Garko 1, Soba 4, and Kolosok which spread across all the agro-ecological zones. Strains fromsuch locations have high potential for use as inoculants. A total of 350 strains of rhizobia were isolated following standard procedures. The strains were assigned culture collection numbers SAMFIX 1-350 and characterized based on their colony morphology which included: colour, shape, size, elevation, margin, texture and opacity. The growth rate was also assessed and 94% were found to be fast growers while 6% were intermediate growers. A total of 20 strains were characterized based on their physiological properties which included, pH, temperature and salt tolerance.. Four strains were found to grow well at pH 4.0, fourteen of the strains grew weakly while two strains did not grow at all. At pH 8.5, eighteen of the strains grew weakly while two did not grow at all. For the temperature, seven of the strains were able to grow well at 8oC, eleven strains grew weakly while two strains did not grow at all. At 35oC only two strains grew well, twelve strains grew weakly while six strains did not grow at all. Also as the concentration of NaCl increased from 1% to 3%, some strains were still able to grow while others did not. However, three strains did not grow even at 1% NaCl. The results show the diversity of rhizobia in the three agro-ecological zones and also their potential for use as inoculant based on their tolerance to extreme pH, temperature and salinity