Genetic Variation in Fruit-to-Grain Conversion Efficiency in Coffea canephora: Heritability, Temporal Instability, and Divergence in Robusta Hybrids and Conilon

The efficiency of converting ripe fruits into processed beans is an economically relevant component of Coffea canephora production systems, yet its genetic parameters remain poorly characterized in studies that do not partition the genotype × year (G×Y) interaction. This study estimated genetic parameters for five processing efficiency traits, namely grain proportion (% grain), husk proportion (% husk), fruit fresh mass per grain mass (FWM/GW), fruit fresh mass per bag (FWM/bag), and fruit volume per bag (FVol/bag), in 48 C. canephora genotypes (40 Robusta, 8 Conilon) evaluated over two crop years (2023–2024) in Jaguaré, Espírito Santo, Brazil. Bayesian inference via MCMC (brms) revealed that the genotype × year variance component exceeded the genotypic variance in 79–97% of posterior samples across the 48 genotypes evaluated over two crop years, a result that should be interpreted within the context of this restricted temporal window, with median heritabilities of 0.27–0.50 (95% credible intervals spanning up to 0.66 units, reflecting the uncertainty inherent to the two-year evaluation window) and genotypic correlations of 0.19–0.38 between years, indicating low consistency of genetic merit across crop seasons. Bayesian probability of consistent superiority identified Z21 as the genotype with the highest predictability for FWM/bag (prob. =0.846 at 20% selection intensity), while VR3 showed a favorable profile across four traits simultaneously. The multi-trait model with unstructured covariance estimated a negative genetic correlation between % grain and FWM/bag (r^g=−0.87), suggesting potential for indirect selection. UPGMA clustering based on Mahalanobis distance (CCC =0.813) yielded six divergence groups that did not coincide with the botanical classification Conilon/Robusta. In this single-location, two-year study, temporal instability was the predominant source of uncertainty in the selection for processing efficiency in C. canephora under restricted evaluation windows. under restricted evaluation windows. Accordingly, the highlighted genotypes should be interpreted as priority candidates for validation in multi-environment, multi-year networks, rather than as definitive cultivar recommendations, given that the short evaluation window limits the generalizability of genotypic rankings.