Enhancing Cowpea Production through Arbuscular Mycorrhizal Fungi Inoculation and Wide Interspecific Crosses

Abstract

Cowpea is a multipurpose legume crop that serves as human food, livestock fodder, and income source and is widely produced in sub-Saharan Africa. Soil fertility and attack by insect pests and diseases are significant limitations to its production. Although farm inputs such as phosphate-rich fertilizers and pesticides can solve the mentioned constraints, they are costly for resource-poor farmers. This study aimed at determining the effect of arbuscular mycorrhizal fungi inoculation on AMF root colonization and growth of cowpea. Additionally, it aimed at developing an insect-pest resistant hybrid by crossing the cultivated cowpea (Vigna unguiculata) with a wild (Vigna vexillata) accession. Pot experiments were set up in a completely randomized design using a wild cowpea species (Ni935) and three cultivated cultivars (Katumani 80, Kunde Mboga and KenKunde 1). There were two treatments; mycorrhizal treatment using a commercial inoculum comprising of four mycorrhizal species, Rhizophagus irregularis, Funneliformis mosseae, Glomus aggregatum and Glomus etunicatum and non-mycorrhizal treatment (control). The pots were maintained in a greenhouse for 30 days prior to harvesting. Data on percentage root mycorrhizal colonization, root and shoot dry weights, nodule number and nodule dry weight were recorded. The dried shoots were also analyzed for N, P and K content. Hybridization experiment was done by crossing the cultivated cowpea cultivar (sp 219) with five different wild accessions (Ni935, Ni936, 263, V268 and AC305) to form immature hybrid pods. Data on pod retention frequencies was recorded. All the data collected from the greenhouse experiment was tested for homogeneity of variance then analyzed by two-way ANOVA and Pearson correlation. Results showed a statistically significant effect of genotype and AMF inoculation on percentage root AMF colonization (p<0.001) as well as on other growth parameters. The cultivated cultivars were more susceptible to AMF colonization and had higher root and shoot dry matter content and nodulation compared to the wild species. There was a positive correlation between AMF colonization and the levels of shoot P and N. Shoot P and N nutrition was also higher in the cultivated cultivars than the wild species. Hybridization experiment revealed differences in pod retention among different accessions of Vigna vexillata. However, an insect-pest resistant hybrid was not generated, possibly due to post-zygotic barriers related to interspecific crossing. This study has demonstrated the importance of AMF inoculation in improving cowpea’s performance. Moreover, it has shown that the cultivated cultivars are still more responsive to mycorrhizal inoculation than the wild species. This is contrary to previous studies that have shown that modern breeding programs may result to suppression of mycorrhizal colonization. Therefore, there is the need to screen different cowpea cultivars and other crops for mycorrhizal symbiosis.