Genotype-environment interactions shape leaf functional traits of cacao in agroforests

The outbreak of frosty (Moniliophthora roreri) and black pod (Phytophthora
palmivora) in Central American cacao agroforests throughout the 1980s, led
to the breeding of Theobroma cacao clones resistant to these diseases.
However, while clonal disease resistance has been well documented, clonal
adaptability to contrasting pedoclimates remains less understood. Plant
functional responses to environmental constraints can be assessed by
evaluating intraspecific trait variation (ITV), but trait-based approaches
have rarely been implemented in genotype assessments. The objective of our
study was to determine cacao clone ITV in contrasting environments. Here,
we used bivariate, multivariate, and functional trait space analyses to
quantify ITV in nine leaf functional traits, among six disease-resistant
cacao clones, growing in two clonal gardens with distinct environmental
characteristics (a “Mild dry season” with near-optimal cacao growing
conditions, and a “Harsh dry season” site with sub-optimal conditions).
All leaf traits varied among the six clones, though trait differences
among clones differed depending on the site: physiological trait
differences among clones were largest at the “Mild dry season” site,
chemical trait differences were widest at the “Harsh dry season” site, and
morphological trait differences among clones were similar at both sites.
Multivariate and hypervolume trait space analyses revealed greater site
influence on trait values of the least productive clones, while the most
productive clones were characterized by higher specific leaf area,
independent of the site. To our knowledge, our paper is among the first to
show evidence that functional traits provide new insights into Genotype x
Environment interactions and clonal selection in agroforestry systems and
support in favor of applying functional trait-based research to plant
breeding paradigms.