Population Characterisation and an Evidence-based Seed-source Strategy for Wild Coffea eugenioides in Nyungwe and Cyamudongo Forests, Rwanda

Abstract

Aims: To characterise the population structure and reproductive output of wild Coffea eugenioides in two Rwandan forests and to determine whether a seed-based Breeding Seed Orchard (BSO) or a graft-based Clonal Seed Orchard (CSO) is the more appropriate seed-source strategy for establishing an orchard of this threatened crop wild relative. Study Design: An observational, cross-sectional field assessment of candidate mother trees was undertaken. Place and Duration of Study: Nyungwe Forest National Park and the isolated Cyamudongo fragment, south-western Rwanda; May 2026, under the RTRP-Seed (IKI) and TREPA (GCF) projects implemented by Landscape Alliance (CIFOR & ICRAF in action). Methodology: Fifty-nine fruit-bearing plus-trees (42 in Nyungwe, 17 in Cyamudongo), spaced ≥ 70 m apart, were georeferenced and measured for structural, phenological and reproductive traits using a structured KoBoToolbox questionnaire; whole-canopy cherry load was the measure of reproductive output. Data were analysed in R using the Mann–Whitney U test, Pearson correlations and multiple linear regression; significance was evaluated at α = .05. Results: Reproductive output was low and highly variable: the median tree carried 29 whole-canopy cherries, 31% carried 15 or fewer, and the coefficient of variation exceeded 110%. Stem diameter was the only significant structural predictor (P = 0.015; r = 0.31), yet the full model explained only a quarter of the variance. Trees in the isolated Cyamudongo fragment carried significantly fewer cherries than those in Nyungwe (medians 15 versus 32; P = .021), and every sub-optimal on-tree seed-quality rating occurred in the fragment. Conclusion: Low, asynchronous fruiting that is weakly related to tree size makes seed-based BSO establishment unreliable. The evidence supports a Clonal Seed Orchard, established by grafting selected wild scions onto locally adapted Coffea arabica rootstock, which captures the full genotype of each selected tree, shortens time to flowering, secures germplasm ex situ, and aligns with Rwanda’s restoration and climate commitments.