Nodulation Responses of Four Food Crop Legumes to Cross-inoculation in the Guinea-savannah (Ngaoundere-cameroon) and Sudanian (Sarh-Chad) Zones

Abstract

A cross-inoculation study on groundnut (Arachis hypogaea L.), bambara groundnut (Vigna subterranea L.), cowpea (Vigna unguiculata L.), and soybean (Glycine max L.) was carried out to screen potentially hight nodulating and nitrogen fixing Rhizobium strains suitable for important crops legumes in the Adamawa region (Cameroon) and middle-Chari region (Chad). The experiment was displayed in a complete Randomised Block with 6 forms of inoculation representing the treatments, each of which was replicated four times. An experimental field consisted of 4 blocks, each rcorresponding to a specific crop legume, which was submitted to each of the following treatments: the control (Ctrl); Groundnut Rhizobium (GR); Cowpea Rhizobium (CR); Soybean Rhizobium (SR); bambara groundnut Rhizobium (BR); and the mixture of these 4 rhizobia (MR). The cross-inoculation types consisted of taking Rhizobium isolates from each crop legume and coating with each of the seed crop before sowing (GR/cowpea/soybean/bambara groundnut, CR/groundnut/soybean/ bambara groundnut, BR/cowpea/soybean/groundnut, SR/cowpea/groundnut bambara/ groundnut, MR/groundnut/cowpea/soybean/Bambara groundnut). Cross-inoculation significantly (p = 0.001) improved the number, efficiency and dry weight of the nodules in all the crop legumes. The responses to nodule efficiency differed from one treatment or host plant species to another. In our investigation to the speculation whether one rhizobial strain can nodulate several crop legumes, we found out that groundnut can be inoculated with SR/BR in Cameroon, or CR/BR in Chad, whereas CR/BR/MR were the best trains to be associated with cowpea both in Cameroon and Chad. Farmer could also use CR/SR in Cameroon and SR/BR in Chad to inoculate soybean, or inoculate bambara groundnut in Cameroon and Chad with GR/BR. All the four crop legumes are thus considered as are promiscuous since each can form symbiotic associations with rhizobia from many other hosts. Selecting these highly effective rhizobia is an important step toward commercial inoculants production for biological nitrogen fixation research in our developing world context.