Studies On Molecular Genetics Of Channel Catfish (Ictalurus Punctatus) Germplasm In China

Channel catfish (Ictalurus punctatus) belongs to phylum Chordata, class Actinopterygii, subclass Neopterygii, order Siluriformes, family Ictaluridae, genus Ictalurus,which was native to America and Northern Mexico. After introduced in 1984, it mainly distributed in more than 20 Provinces from China, and had high output. In recent years, for the reason of human breeding, there has come out a series of problems of the Channel catfish populations, such as decline resistance to disease , slow-growing, and easy to have large-scale plant disease, the death when high density intensification cultivation, and so on. To increase the output and the quality of the breeding Channel catfish, ensure the sustainable development of the Ictalurus's breeding Project, it has been a growing interest issues of improving the quality, increasing the genetic diversity of the Channel catfish. DNA molecular marker is able to express genetic information accurately for its excellence of stability, accuracy and security.In this paper, four domestic stocks of populations of Channel catfish were studied by means of AFLP and SSR (microsatellite) molecular marker techniques. They were the population in Fuzhou province and Hubei province which introduced in 1984(P1984), the population in Fuzhou province and Liaoning province which introduced in 1997(P1997), the population in Hunan province which introduced in 2004(P2004), and the population in Fuzhou province which was cross breeding between P1984 and P1997 (P8497). We hope that these results will provide the theory basis for inherited domestic of Channel catfish.One hundred and twenty Channel catfish from four populations (thirty individuals per population) were analyzed using ten AFLP primer combinations and ten SSR primers respectively. AFLP and SSR banding patterns were transformed into binary data and matrices were processed by Popgene32 program. Using the data obtained, the genetic diversity and the genetic structure were estimated, the similarity coefficient was calculated and UPGMA clustering analyzed on computer among these Channel catfish varieties. Results of two techniques are as follow:With the test of polymorphism for AFLP markers, total 523 loci were amplified using 10 primer combinations, and 243 were polymorphic loci. On average, 24.3 polymorphic bands are amplified by one primer combination. As for the SSR primers, 35 alleles were amplified with 3.5 alleles each one. Both of the two techniques showed medium genetic diversity in all populations. Genetic parameters calculated by SSR technique were obviously higher than that of AFLP technique. The effected alleles number (Ne) of AFLP and SSR were 1.2026 and 2.1098, observed heterozygosity ranged from 0.0781 to 0.1137 across populations for AFLPs and from 0.4768 to 0.5982 for SSRs. There was a trend of heterozygosity excess in all the populations detected by SSR technique, with the observed heterozygosity and expected heterozygosity were 0.5249 and 0.5161, respectively. Although there were some distinctness between the two techniques, the trend of the genetic diversity parameters among four populations which computed by two techniques were difference: P8497>P1997>P2004> P1984 by AFLP, P2004>P1997>P8497>P1984 by SSR, P1984 population had the lowest genetic diversity among all the populations by both AFLP and SSR.The average value of Gst coefficient of the AFLPs was 0.0957. The coefficient of inbreeding (Fst) among the seven populations were 0.0196 of SSRs, which means that 1.96﹪genetic variation of the whole population came from the genetic differences among the seven populations. The Gst coefficient ranged from 0.0798 to 0.1192, and the Fst among all the populations ranged from 0.0054 to 0.0357. And the Gst and Fst statistics data by two methods revealed no significant divergence between all pairs of populations. The Nm in populations from Gst and Fst were 4.8404(AFLP) and 23.3290(SSR) which were proved well gene flow among populations.Genetic distance among the 4 populations ranged from 0.0079 to 0.0158 of AFLPs and 0.0066 to 0.0632 of SSRs, the phylogenetic trees of four populations suggested that,like the genetic distances, P1997 population was closer to P2004 population, and they were clustered together as the first group. P8497 population was clustered into the second group, the last one was P1984 population.Comparison of the two techniques SSR and AFLP in the study of genetic diversity and genetic structure between populations of Channel catfish has been taken. The AFLP marker system revealed lower polymorphism information content (PIC) and effective numbers of alleles per locus (Ne) than that of SSR. But it has a much higher polymorphic banding patterns and assay efficiency index highly correlated. The results indicated that both AFLP and SSR techniques are useful tools for the analysis of the genetic diversity of. Channel catfish.