The Correlation between the Efficiency of Rhizobia and Nitrate Reductase and Dehydrogenase Activities of Cowpea Nodules

Abstract

Cowpea seeds variety Fettriat were planted in Nile silt soil and inoculated with 5 strains of cowpea rhizobia. After 50 and 80 days, the plants were uprooted, analysed for dry weight, total nitrogen, fresh weight of nodules, nitrate reductase activity in the leaves, and nitrate reductase and dehydrogenase activities in the nodule homogenate in the presence or absence of succinate, citrate, and ethyl alcohol. The data were analysed to establish the correlation coefficients between total nitrogen and other characteristics. A significant positive correlation existed between total nitrogen and fresh weight of nodules in both cuts (after 50 and 80 days). The correlation was significant between total nitrogen and dry weight of the plants in the first cut, but was non-significant in the second one. Nitrate reductase activity in leaves and nodule homogenates in the presence of different hydrogen donors were positively correlated in the first cut and negatively correlated in the second one. Nitrate reductase activity in the leaves was much less than that in the nodule homogenates. A negative correlation was noticed between phenol content of the nodules and total nitrogen. In the first cut, while the correlation between total nitrogen and dehydrogenase activity in the presence of citrate or absence of any hydrogen donors was positive, it was negative with ethanol and succinate. In the second cut, however, all the dehydrogenase activities were negatively correlated with total nitrogen.