Abalones are important farming species with a high economic value. They have already been farmed for more than 50 years. As problems and new requirements rose continuously in culture industry of abalone, studies on genetic and breeding techniques are needed to improve characteristics and to gain new traits. This review concentrates on advances in genetics and breeding techniques in abalone. As for genetic studies, karyological analyses, allozyme, DNA markers and genetic diversity were reviewed. So far, karyological analyses in abalone have been performed in 12 species that can be divided into three groups according to the chromosome number. In some economically important species, loci of allozymes and. microsatellites have been isolated and applied to investigate the genetic structure of natural and hatchery populations and to identify the result of chromosome set manipulation, but the related reports are only a few yet. The resultsof investigation with DNA markers and allozymes showed that the genetic structure of natural populations presents two characteristics: excessive homozygosity and subdivision. Advances of various breeding techniques, including introduction, selection,hybridization, polyploidy, gynogenesis and gene manipulation, were reviewed in the other part. Although Haliotis discus discus, introduced from Japan, has become one of the most important culture species in China, the economic, social and environmental effects of introduction have been rarely studied. Selection is one of the most important and basic breeding techniques, but the studies on selection are only a few and preliminary, referring to the relations between genetic characteristics and the traits of growth and resistance, genetic diversity and heritability of quantitative traits, and the effect of selection. Interspecific hybridization was the first breeding program carded out in abalone. Experimental hybridization have been carded out for about 20 crosses. Heterosis,such as faster growth and high survival rate, has been observed in some crosses. Triploids have been successfully induced in many species of abalone with physical or chemical shock, e.g.H, discus hannai, H. rufescens, H.diversicolor diversicolor and H. rnidae. Field experiments were conducted in some species of triploid abalone. In comparison with triploid, the research on tetraploid is still in quest stage. The progress of induction of gynogenesis in abalone is quite slow. Conditions of sperm inactivation, diploid restoration and nuclear behavior of gynogenetically activated eggs have been researched on in H. discus han nai. Notwithstanding the gene transfer technology in abalone is in the quest stage, the research have already involved preparation of exogenic DNA,means of gene transfer, identification integration and expression of target gene, etc. Three research directions in these topics were proposed : to investigate the germplasm resources of abalone deeply and widely, to make use of traditional breeding methods and modem biotechnique synthetically, and to combine the science research with production practice.
展开▼
