Yield stability in clones of Coffea canephora in the short and medium term: longitudinal data analyses and measures of stability over time

Abstract

In perennial crops like coffee, genetic improvement efficiency is limited by several factors. These include determining the acceptable minimum observation period for yield traits, and also variation of the traits over time, in order to develop breeding objectives that incorporate stability and persistence of the desired traits. Yield data from a trial comparing 20 Coffea canephora clones in Ivory Coast, monitored over nine production years, were analyzed by two different methods. (1) After studying genetic correlations between yields in successive years, longitudinal data analyses were applied to understand relationships between years. Several models were tested and the Compound Symmetry model, with heterogeneous variances (CSH model), best described the data structure. For instance, at tree level, correlations between yields of the different years were moderately stable, which revealed a major tree effect within clones. (2) Subsequently, derived index traits were considered, characterizing yield distribution over the different years. The traits involved were earliness, alternation, and the intensity of variations between years. Despite a marked tendency towards biennial cropping, especially in the early years, the estimated genetic correlations between years, and between individual years and cumulative yield were generally high. The intensity of the relative differences between yields in successive years was heritable only in the second production cycle. Despite some clonal differences in yield-stability variables, clonal yields in single years or groups of years evidently reflected both cumulative yields and comparative yield stability.