Assessment of genetic and phenotypic diversity of the giant kelp, Macrocystis pyrifera, to support breeding programs

The accelerated development of seaweed aquaculture is stimulating research on the genetic drivers of phenotypic diversity of the target species, in order to optimize breeding strategies, to help determine the choice of source populations, and for the selection of traits and varieties that fit with the environmental variability of the production site. This study investigates the spatial variation of the genetic and phenotypic diversities in natural populations of the giant kelp Macrocystis pyrifera, and evaluates the potential for modifying agronomic traits through controlled breeding. Nine microsatellites and 12 morphological traits were used to describe the distribution of diversity present along the Southeastern Pacific (SEP) Coast. We expected concordant patterns of spatial discontinuities if the genetic background was driving morphological divergence across habitats. Crossing experiments were made to assess the heritability of specific traits and evaluate the performance of the F1 generation in the laboratory and in open sea cultivation respectively. Our results revealed four genetic clusters along the latitudinal distribution of M. pyrifera populations, tightly correlated with the existence of major environmental discontinuities. These clusters also matched clusters of morphological diversity, suggesting that both morphological and genetic diversities responded to the same environmental drivers. In crossing experiments, no significant differences were detected between selfed and outbred F1, in morphology, growth and chemical components, but a high variability among all different crosses was observed, revealing a high degree of heritable phenotypic variance. Although, the results suggest that the morphological variation of Macrocystis along the SEP coast is strongly driven by the genetic background. Our controlled crosses were also indicative of a high potential for using this genetic variability in breeding programs for sustainable aquaculture development.