Estimates of genetic parameters and genotype by environment interactions for shell nacre color and growth traits in the purple freshwater pearl mussel Hyriopsis cumingii

Hyriopsis cumingii, one of the most commercially important freshwater pearl mussel in China, produced most of white and orange cultured pearls. However, purple freshwater cultured pearls, with higher commercial value, are the most popular due to its rarity. For increasing the yields of purple pearl, one selection breeding program for improving shell nacre color were developed in H. cumingii. Genetic parameters and genotype by environment interactions for shell nacre color and growth traits were estimated from the fifth-generation purple selective strain of H. cumingii reared at two sites (Chongming and Jinhua). Four shell nacre color parameters and six shell growth traits were recorded by 1142 individuals at 12-month-old. Microsatellite-based DNA parentage analysis was used to assign the mussels to 13 paternal half-sib families, including 37 full-sib families. Genetic diversity was found to be high in the selected strain, with a mean expected heterozygosity at 6 microsatellite loci equal to 0.791. Heritability estimates of four shell nacre color parameters, lightness (L*), redness (a*), yellowness (b*), and total color change (dE) were 0.33 ± 0.19, 0.17 ± 0.10, 0.69 ± 0.10, and 0.33 ± 0.19, respectively. Heritability estimates were 0.20 ± 0.03 for shell length, 0.16 ± 0.06 for shell height, 0.17 ± 0.02 for shell width, 0.23 ± 0.01 for body weight, 0.15 ± 0.06 for mantle weight, and 0.31 ± 0.03 for shell weight. No significant phenotypic or genetic correlation was found between shell nacre color parameters and growth traits. All shell nacre color parameters and growth traits, except for shell nacre color parameter b*, exhibited may be significant genotype by environment interactions at the two sites. The results suggest that shell nacre color parameters may be treated as selective traits for further improving shell nacre color. And shell nacre color may be selected for independently of selection on growth performance. Some considering to the likely genotype by environment interactions for shell nacre color and growth traits should be taken in future selective breeding programs for large-scale culture practices.