Morphological Diversity and Trait-Based Characterization of Coffea canephora Accessions in the CRIN Germplasm Collection: Implications for Genetic Improvement

Background Coffea species (Coffee) is one of the most economically important agricultural commodities universally. In Nigeria, Coffea canephora is the dominant species, accounting for about 95% of coffee exports, yet its morphological diversity remains poorly documented. Understanding phenotypic variability is vital to developing novel breeding programmes for crop improvement. This study therefore assessed the morphological diversity of C. canephora accessions collected from Cocoa Research Institute of Nigeria germplasm and Nigerian coffee farmers. Results Forty-three accessions of C. canephora , comprising seven morphological classes (Gold Coast, Java Robusta, Java ex-Gamba, Togolese, Kouillou, Niaouli, and Uganda Robusta), plus a small set of accessions of unresolved morphological class, were characterised using thirteen morphological traits (four quantitative and nine qualitative) following International Plant Genetic Resources Institute descriptors. Principal component analysis showed PC1 explaining 66.9% of the variance (height to first branching as the primary contributing trait) and PC2 explaining 18.2% (leaf length as the primary contributing trait). Cluster analysis grouped the accessions into three distinct classes, with 40 accessions expressing broad genetic variation, one genetically distinct accession (C90), and two closely related accessions (ORANRE 1 and ORANRE 2) separating from the main population. Qualitative traits showed clearly differentiated frequency distributions across categories of plant habit, branching pattern, leaf shape, and berry characteristics, described in detail in Results. Conclusions Substantial morphological diversity exists among C. canephora accessions in Nigeria, with plant height and leaf length identified as the principal phenotypic traits for discriminating accessions. These findings provide a foundational trait-based framework for selecting superior accessions and designing targeted genetic improvement programmes for Nigerian robusta coffee.