耐盐罗非鱼育种回交效应评估

Evaluation of backcrossing breeding effect in selection of salt-tolerant tilapia

对罗非鱼2种回交子代、2种正反交子代（回交鱼的母本）、2种原始种（回交鱼的祖父、母本）,共6种遗传型的生长特性、耐盐特性及遗传特征进行了研究。结果表明：（1）在盐度15、20及25时,2种回交子代的日均增重率皆比母本提高了30%~45%,差异显著（P=0.023）。（2）SSR分析发现,2种回交子代接受尼罗罗非鱼（Oreochromis niloticus）的遗传特征带分别为87.5%和79.2%,接受萨罗罗非鱼（Sarotherodon melanotheron）的分别为35.2%和41.2%;而2种正反杂交子代接受尼罗罗非鱼的分别为66.7%和41.7%,接受萨罗罗非鱼的分别为47.1%和88.2%。（3）回交子代与原始亲本尼罗罗非鱼的遗传距离较近,同正反交子代相比,回交子代生长性能有所进步,耐盐性能基本保持,扩增的特异性条带数目较少,表明遗传多样性走低和基因型纯合性走强的趋势。（4）两种回交子代间有一定差异,萨尼♀[萨罗罗非鱼♀×尼罗罗非鱼♂（F2）]×尼罗罗非鱼♂生长快5%,有效等位基因数、平均杂合度、多态信息含量等遗传指标较高,是优选的对象。

In order to understand the effects of backcrossing on economic trait improvement in selection of salt- tolerant tilapia,studies on the growth performance, salt-resistant performance and hereditary characters were carried out by using 6 genotypic tilapias including two types of backcross, two types of reciprocal crosses（ maternal sides for backcrosses）, and two types of original species（ grandparents of backcrosses）. The results showed that：（ 1）Under the salinities of 15,20 and 25, the average daily weight gain of two backcrosses were 30%-45% higher than the maternal fish（ P=0.023）.（ 2） The SSR analysis indicated that two kinds of backcross received 87.5% and 79.2% of Oreochromis niloticus characteristic bands and 35.2% and 41.2% of Sarotherodon melanotheron characteristic bands respectively; two kinds of hybrids received 66.7% and 41.7% of Oreochromis niloticus characteristic bands and 47.1% and 88.2% of Sarotherodon melanotheron characteristic bands respectively.（ 3）The genetic distance between backcross and their grandmother（ O. niloticus） was closer. Compared with the reciprocal cross, the backcross hybrids showed an increase in growth, a matinace in salnility tolerance, and a decrease in number of amplification specific bands, all indicating that there exists trend of decrease in genetic diversity but an increase in genotypic purification.（4）There are certain differences between two types of backcross, in which（ S.melanotheron♀×O.niloticus♂） ♀ ×O. niloticus ♂ is faster in growth than（ O.niloticus♀×S.melanotheron♂）♀× O.niloticus♂ by 5%, also is higher in number of effective alleles, heterozygosity（H） and polymorphism information contents（PIC）, which indicated that it is a super candidate for further selection.