Analysis Of Growth Traits And Disease Resistance Of Grass Carp Genetic Parameters And QTL Mapping

Grass Carp is the main freshwater aquaculture fish in our country, but its germplasm resources with the large-scale artificial breeding in artificial breeding gradually degenerated, so there are plans to Grass Carp, science is very necessary, the researches related to the parameters of genetic research on the growth and disease resistance Grass Carp, through the different stages of growth traits between the correlation of age, April Grass Carp growth traits and disease resistance of heritability, LEAP-2 gene of SNP and Grass Carp growth and disease resistance of correlation analysis and Grass Carp growth and disease resistance of preliminary QTL mapping. The main results and major conclusion are as followings: 1.The relationship between morphological traits and body weight of grass carp at different month ages.we measured morphometric traits at 2-month-old stage,4-month-old stage,6-month-old stage,12-month-old stage, respectively in this study, The correlation analysis, path analysis and multiple regression were used to calculate correlation coefficient, path coefficient and the coefficient of determination between morphological traits and body weight. Correlation analysis showed that morphological traits and body weight of each month-old grass carp were significantly correlated(P<0.01). Path analysis showed that at 2-month-old stage and 6-month-old stage,the trait with strongest direct effect on body weight was the body height,but at 4-month-old stage,12-month-old stage, the trait with strongest direct effect on body weight was the body length, and all of stages the trait with strongest indirect effect on body weight was body width. The results of determinant coefficient analysis was consistent with that of path analysis. Partial regression coefficient significance test three morphological traits are highly significant, each stage can be established the multiple regression equation relating the body weight. Studies have shown that 4-month-old stage and 12-month-old stage adjusted coefficient of determination is greater than 0.85, the major morphometric traits affecting body weight of grass carp at different growth stages affect body weight have been identified. To provide the basic data for Grass Carp at different growth stages of breeding. 2. Grass Carp of 4-month-stage growth and disease resistance genetic parameters and family comparative analysis.Mixed family on 4-month-stage of grass carp, paternity test, determine the pedigree information. This study through 8 pairs of microsatellite in 1047 individuals of the STR type, the use of Genemapper Version 4.0 software to read the data of molecular weight of microsatellite amplification products, using the software Cervus 3.0 paternity analysis of 1047 offspring of 972 individuals, the results confirmed its male parent, determine the rate of 92.84%. According to the paternity test results obtained 237 full sib families from 22 female and 23 male, 92 full sib families including 779 individuals, individual numbers of each family in the range of 3-89. Heritability of grass carp’s body mass in April 0.3464, the heritability of body length is 0.3313, the heritability of body height is 0.3045, the heritability of body width for the heritability of resistance and survival time of 0.3033 to 0.0597. Usually, H2 <0.15 divided into low heritability levels, 0.15<H2 <0.3 classified as moderate heritability, H2 >0.3 is divided into high heritability, so in April the grass carp body weight, body length, body height and body width are high heritability; heritability of survival time in April of grass carp resistance is 0.0597, belong to low heritability. In April the old grass carp body length and body weight of the largest genetic correlation and phenotypic correlation were 0.9856 and 0.9766, and the length of the body and the survival time of phenotypic correlation and genetic correlation were 0.3482 and 0.3463. Genetic correlation between traits is an important basis for formulating the objective traits, heritability of resistance to the survival time for the low level of heritability, so in the fight against disease breeding performance can through the indirect breeding or molecular marker assisted breeding of body length to achieve the breeding goal. At the same time, the growth performance of good family and long survival time and survival rate high pedigree is a crossover, mainly is the 48 family and 54 family, the parents of the two families were F97832 and M51696, F51566 and M97893, at the same time, growth performance index lower family there the cross is the No. 72 and No. 84 family, the parents of the two families were F51593 and M51341, F97808 and M97846. Therefore, the rational selection of the parents and the elimination of the establishment of grass carp resistance groups to provide a new method. 3. SNPs of LEAP-2 gene and Their Association with the Growth Traits and Disease resistance of Grass Carp.Select the 1000 tails Grass Carp of 4-month-old stage for doing Aeromonas hydrophila challenge test,and record the survival time and growth data. Randomly selected 192 tails survival Grass Carp and 192 tails dead Grass Carp, then extract DNA.According to the LEAP-2 gene primers were designed for PCR amplification. By direct DNA sequencing, after sequence alignment,two SNP mutations were identified after sequencing the PCR prodcts. Site01:631(AGAGAGAGAGAGAGAGAA/-) located in the LEAP-2 gene Upstream of the transcription start point of the 717 bp regulatory sequences, the wild type DD gene type and its survival rate was lower than the mutant II gene type and heterozygous DI type, but the wild type DD gene type growth rate was higher than the mutant II gene type and heterozygous DI type. There were very significant differences in survival rate of different genotype of Site01(P<0.01), in addition to other growth indices of body length outside of the average value of the existence of significant differences(P<0.05). Site02 :1738(CA/-)located in the LEAP-2 gene second introns, the heterozygous gene type DI survival rate was higher than the wild type II gene type, but the heterozygous DI growth rate was higher than the wild type DD gene type. There were significant differences in survival rate of different genotype of Site02(P<0.01), average growth index in addition to body length outside there was significant difference(P<0.05). 5 kinds of double type consisting of Site01 and Site02, there were very significant differences between the survival rate of different double type(P<0.01),average growth rate were very significant difference(P<0.01). The experimental results show that the growth and disease resistance of 2 SNPs and Grass Carp Grass Carp LEAP-2 gene exists significant correlation, Therefore these SNPs can be used for growth and disease resistance breeding. 4. Preliminary mapping of QTL growth and disease resistance traits of Grass Carp.Using microsatellite markers such as developed in this study for the construction of genetic map, and the growth of related characters and carries on the preliminary QTL mapping and disease resistance, this study found that the 7 QTLs related to quality of grass carp body, 8 QTLs related to grass carp body length, four QTLs related to grass carp body length, 8 QTLs related to grass carp body length and four QTLs related to grass carp disease resistance. In the process of economic traits QTL mapping research, found that can explain the phenotypic variation of more than 20% of the QTL main effect for the traits QTL interval, Group19(CID0202-CID0513/CID1536), Group2(CID0223-CID0131A), and Group 24(CID0856-CID1534) can explain the phenotypic variation were 28.8%, 25.2%, 23.1%, is associated with a significant body of quality the main effect of QTL interval; Group19(CID0202-CID0513/CID1536) and Group24(CID0856-CID1534)can explain the phenotypic variation were 29.1%, 23.7%, is associated with a significant length of main effect QTL interval; Group21(CID1114-CID0382) and Group24(CID0856-CID1534) can explain the phenotypic variation were 24.2%, 23.1%, is associated with a significant wide the main effect of QTL interval; Group8(CID0257-EST0006) and Group19(CID0202-CID0513/CID1536) and Group24(CID0856-CID1435) can explain the phenotypic variation were 32.2%, 34.9%, 30.7%, is associated with a significant resistance to the main effect of QTL range. Detected in this study are in the 15 QTL, confidence intervals for 3 to 30 cm, less than 10 cm of seven, at the same time CID0223-CID0131 A, CID0202-CID0513/CID1536 and CID0856-CID1435 and body quality, the main effect of chain length and breadth traits closely QTL interval, which provides a basis for further breeding of grass carp. Closely chain in breeding, use these QTL marker assisted selection, can be modified at the same time for multiple traits, aggregated breeding, achieve the result of get twice the result with half the effort.The research provides sufficient basic data and theoretical basis for indirect selection of grass carp and the molecular marker assisted breeding.