Morphological Characterization of Cameroon Cowpea Genotypes for Nitrogen Fixation Related Traits in Low Phosphorus Soils

Aims: The objective of this study was to characterize cowpea genotypes based on grain yields and nitrogen fixing potentials.

Study Design: The experimental design was a two-factor factorial experiment in a randomized complete block with two replications.

Place and Duration of Study: This study was carried out in the International Institutue of Tropical Agriculture (IITA), Cameroon between June and December 2013.

Methodology: Fifty genotypes of cowpea were collected in 2012 from various sources. The exotic genotypes came from the International Institute of Tropical Agriculture (IITA), Senegalese Agricultural Research Institute (ISRA), University of California, Riverside (UCR); and one genotype evaluated previously at the study site (Danilla). The experiment was carried out in pots in the screen house at Nkolbisson IITA, Cameroon. Soil samples were analyzed for pH, organic C, N, exchangeable Ca, Mg, K, and extractable P .Data was collected for 20 morphological traits related to grain yields, nitrogen fixation and plant growth. Analysis of variance (ANOVA) was performed on all the traits using the GLM of SAS version 9.2. Cluster analysis was done and dendrogram constructed based on the hierarchical method using Euclidean test in SAS version 9.2.

Results: The combined analysis of variance across environments (P-fertilization levels) showed significant effects for most of the traits. In this study, the interaction between genotype and P-fertilization was significant (p< 0.05) for Nsize and very significant (P< 0.01) for LCS, SFW, SDW, RDW, shootp, NN, NFN, FN, NDW, NI, delta N of the legume (δ15N leg), %Ndfa, Shoot N, N-fixed and YLDplt. The genotypes were significantly different for all the traits studied at P< 0.01.Under low P at a dissimilarity coefficient of 1.8, the phenogram distributed the 50 accessions into two major clusters (I, II). Cluster II has only one accession (Kodek. When P fertilizer was applied, the number of clusters and structure of phenogram II did not change but the accessions were regrouped compared to grouping under low P. Here at a dissimilarity level of 1.8, the phenogram also divided the 50 accessions into two major clusters (I, II). Under high P and high N environments, the maximum dissimilarity level between the accessions was 1.6 so grouping was done only at a dissimilarity level of 0.6. The addition of N fertilizers to the high P pots completely changed the phenogram distributing the accessions into 5 clusters.

Conclusion: Cluster analysis substantiated the existence of diversity among the 50 accessions for the morphological traits studied. The clustering pattern showed that the Cameroon landraces were not distant from each other like the exotic accessions. Furthermore, dissimilarities were observed among accessions from the three geographical regions, presenting a great possibility for the development of suitable varieties for the various agro-ecological zones of Cameroon.