Variation in yield over time in a cacao factorial mating design: changes in heritability and longitudinal data analyses over 13 consecutive years
The production period for perennial crops is often indeterminate. For cacao, the production period can last between 15 and 70 years. The implication for breeding is not easy. How many years of production are needed to propose new varieties? How are the production levels of several years linked at tree level? How is it possible to model series of production data over time? To answer these questions, data were analyzed from 13 years’ production in a cacao factorial mating design. Genetic analyses of the number of healthy pods produced per year and per tree revealed that the inheritance of the trait is mainly additive, especially in the first 8 years of production; after this first period, a dominance effect appeared. Yield increased in the first 6 years, then decreased over time. The first major production (4th year) was a good predictor of cumulative yield, with a genetic correlation of 0.98. However, the shape of the yield trajectories varied depending on the families. Longitudinal data analyses were carried out to gain a clearer understanding of the link between the yields of successive years. When considering all 13 years, the best fit model was the antedependence model; this model indicated that the correlation between 2 successive years was stable, and the correlation between years decreased as the gap between years increased. When the first 3 years were not taken into account, the best fit model was a Compound Symmetry model, which indicated a large tree effect over time.
KeywordsBreeding methods Fruit production Genetic correlations Mixed model Repeated data analyses Theobroma cacao
We should like to thank the organizations associated with this study, notably the Centre National de Recherche Agronomique (CNRA) in Côte d’Ivoire and Peter Biggins for reviewing the English version.
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