Donor-oyster derived heritability estimates and the effect of genotype × environment interaction on the production of pearl quality traits in the silver-lip pearl oyster, Pinctada maxima

The silver-lip pearl oyster, Pinctada maxima, produces the largest and most valuable pearls in the world. Despite the importance of this species very little is known about genetic parameters of commercially important pearl traits. As an initial step towards developing a selective breeding program, site selection effects, donor oyster derived genetic parameters and genotype by environment (G×E)interactions were estimated for pearl quality traits of P. maxima, originating from three populations (Aru, Bali, West Papua), reared at two commercial grow-out locations in Indonesia (Bali and Lombok). Microsatellite-based DNA parentage analyses were used to assign oysters to families and population of origin. Six pearl traits that are together the major determinants of pearl value (pearl weight (g), size (mm), shape, colour, complexion and lustre) were recorded at harvest. Pearls produced at the Lombok site were bigger and more valuable compared to pearls produced at the Bali site (P<0.05). G×E interactions were present for size (r _g=-0.22), colour (r _g=0.28), weight (r _g=0.38), shape (r _g=0.56) and lustre (r _g=0.59) due to re-ranking of relative family performances at the two sites, although there were large standard errors associated with these estimates. Complexion was the only trait that showed little evidence for re-ranking (r _g=0.85). Donor related-heritability estimates for size (h ²=0.13), lustre (h ²=0.14), weight (h ²=0.15), colour (h ²=0.15) and shape (h ²=0.06) were low, while for complexion estimates were moderate (h ²=0.25). A positive and high genetic correlation was found between pearl size and weight (r _g=0.99), shape and complexion (r _g=0.65) and shape and colour (r _g=0.62); however, interestingly pearl weight was negatively genetically correlated with shape (r _g=-0.46), complexion (r _g=-0.11), colour (r _g=-0.03) and lustre (r _g=-0.15). Given the complex relationship amongst pearl quality traits and the likelihood for G×E interaction effects care should be executed when designing breeding objectives for the genetic improvement of these traits in P. maxima.