Evidence of donor effect on cultured pearl quality from a duplicated grafting experiment onPinctada margaritiferausing wild donors

Abstract

-Producing high quality cultured black pearls from Pinctada margaritifera is one of the major challenges for the "pearl oyster" industry in French Polynesia. In order to assess donor effect on cultured pearl quality, wild Pinctada margaritifera originating from the Tuamotu Archipelago were used in a duplicated grafting experiment. After 12 months of culture, nucleus retention was assessed and seven pearl quality traits recorded on the 454 cultured pearls harvested from the experiment. The traits scored were nacre thickness and pearl weight, surface defects, lustre, grade, and the colour components: 1) darkness of cultured pearl colour, and 2) visual perception of colour class (bodycolor and/or overtone). Our results demonstrate for the first time that individual wild donors of implanted mantle grafts significantly affect these seven quality traits in P. margaritifera cultured pearls. This finding was repeated in two series of grafts made by different professional grafters. The wild donors could be ranked from "best" (e.g., the donor whose grafts produced the cultured pearl with the maximum lustre) to the "worst". Moreover, we showed strong correlations between: 1) cultured pearl nacre thickness and grade, with grade A showing the greatest nacre thickness on average compared with grade D and rejects; and 2) nacre thickness/cultured pearl weight and colour components (darkness and visual "colour categories"), with the palest cultured pearls (i.e. white cultured pearls) being the smallest (lowest nacre thickness and weight). Thus, one way of enhancing P. margaritifera foundation stocks for a selective breeding program could be to select the "best" donors, using appropriate molecular tools. Generation of selected donor lines from these stocks through hatchery production would be one way to increase the quality of cultured pearl farming of P. margaritifera in French Polynesia.

Family effect on cultured pearl quality in black-lipped pearl oysterPinctada margaritiferaand insights for genetic improvement

“…The main result is that highly significant progeny effects exist for several traits of interest: nucleus retention, nacre thickness, nacre weight, pearl darkness, visually perceived pearl colour (bodycolor and overtone), pearl shape categories, surface defects and lustre, the last two of which are components of the Tahitian classification grade. These results are consistent with those obtained by Tayale et al (2012) where the authors demonstrated in a duplicated experimental graft, that individual wild donors of implanted mantle grafts significantly affect seven of the studied quality trait in P. margaritifera cultured pearls (pearl shape categories were not studied in Tayale et al 2012). In contrast, no significant progeny effect was recorded for oyster mortality or pearl circles.…”

“…These data are consistent with those of Tayale et al (2012) on P. margaritifera wild donors, where: 1) extreme nucleus retention rate were comparable with 51% to 77% and 2) wild donors had a significant effect on nucleus retention. Cochennec-Laureau et al (2010) have already suggested that rejection phenomena are linked to a number of causes, among which choice of donor oyster is important.…”

“…Two kinds of colour evaluation (without loupe) were made on the cultured pearls (Tayale et al 2012):…”

“…A study on P. margaritifera using wild donors showed evidence of a donor effect on cultured pearl quality (Tayale et al 2012). Among "pearl oyster" species, few breeding programs have been conducted to select for improved donor oysters as a means to improve proportion of high quality cultured pearls and those that have been carried out have focused on the Akoya "pearl oyster" (P. fucata) and the silver-or gold-lipped "pearl oyster" P. maxima species.…”

Shell Growth Performance of Hatchery Produced Pinctada margaritifera: Family Effect and Relation with Cultured Pearl Weight

“…Shell and cultured pearl formation result from the bio-mineralization activities of two distinct tissues in a grafted pearl oyster: the mantle of the recipient oyster and the pearl sac built from graft tissues from the donor [5]. The pearl weight finally attained depends on several factors, including whether or not the donor oyster originated from the wild [8] or from a hatchery-produced family [9,10]. Some studies have shown phenotypic correlations between pearl weight and recipient oyster shell traits, e.g., for Pinctada fucata [11][12][13].…”