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

Coffee is one of the world's most cherished crops, a daily ritual for millions that shapes economies and cultures from the tropics to the temperate zones. While many people know coffee by its two famous faces—the delicate Arabica and the hardy Robusta—less is known about the specific varieties growing within individual countries. In Nigeria, the Robusta variety dominates the landscape, accounting for nearly all of the nation's coffee exports. Yet, despite its economic importance, the genetic story of these plants has remained largely untold. Farmers and scientists have long suspected that the coffee bushes growing in different regions hold unique traits, but without a clear map of their physical differences, it is difficult to breed better, more resilient crops. Understanding the visible characteristics of a plant, such as how tall it grows, the shape of its leaves, or the color of its berries, is the first step in unlocking its potential. These physical features are not just cosmetic; they are clues to how a plant survives drought, resists disease, or produces a better harvest.

To uncover the hidden diversity within Nigeria's coffee, a team of researchers from the Cocoa Research Institute of Nigeria and the University of Ibadan set out to examine forty-three distinct coffee accessions. These accessions, which are essentially specific collections of plants representing different genetic lines, were gathered from three major coffee-growing regions: the research institute's main repository in Ibadan, a substation in Cross River State, and the actual farms of local growers in Kogi and Ekiti States. The scientists treated each plant like a unique individual, measuring its height from the ground to its first branch and recording the thickness of its stem. They also carefully documented the size and shape of the leaves, the color of new shoots, and the appearance of the berries. By comparing these physical traits across the different groups, the researchers aimed to see how much variety existed and to identify which specific features could help breeders select the best plants for the future.

The investigation revealed a landscape of striking variation. The coffee plants in the study ranged dramatically in size, with the shortest reaching just over ten centimeters in height and the tallest stretching nearly forty-eight centimeters. The leaves showed similar diversity, with widths varying from about six centimeters to over thirteen centimeters. The researchers found that while some traits, like the length and width of a leaf, tended to grow together, other features, such as the overall height of the plant, did not necessarily predict the size of its leaves. This means that a tall plant does not automatically have large leaves, and a short one does not guarantee small ones. The study also looked at the "personality" of the plants, noting that most grew as shrubs or small trees, with a few distinct bushes. While every single plant in the collection shared the same bright green color for its new shoots, the berries displayed a vibrant array of colors, including orange-red and purple-red, offering a visual spectrum of the genetic wealth available.

To make sense of this complexity, the researchers used a method that grouped the plants based on their overall similarity, treating both their measured dimensions and their visual characteristics as a single picture. This analysis sorted the forty-three accessions into three clear groups. The largest group contained forty plants that, while diverse, shared a broad genetic connection. Within this massive cluster, some pairs of plants were nearly identical twins, while others were more distant cousins. One plant, however, stood entirely apart from the rest. This specific accession, known as C90, was the shortest in the entire collection and possessed a unique combination of traits that set it apart from every other plant studied. It represents a rare genetic resource, a distinct outlier that could be invaluable for introducing new characteristics into breeding programs. A third, smaller group consisted of two plants from a farmer's field that were so similar to each other they formed their own tight pair, yet remained distinct from the main population.

The study concludes that Nigeria's coffee resources are far more diverse than previously documented. The researchers identified plant height and leaf length as the most powerful tools for telling these different varieties apart. These findings provide a solid foundation for the next steps in coffee improvement. By knowing exactly which plants are unique and which traits they carry, breeders can now make informed choices about which plants to cross to create new varieties. The goal is to develop coffee that is not only productive but also better suited to the changing climate and the needs of Nigerian farmers. This work transforms a collection of plants from a simple inventory into a strategic resource, ensuring that the future of Nigeria's coffee industry is built on a deep understanding of its own genetic heritage.