Study On Genetic Diversity And Correlation Of Hybrid Parents And F₁ In Walnut

Walnut(Juglans regia L.) is the world's famous nuts and oil plant.Sichuan is the main distribution of walnut populations and has unique advantages of breeding resources.Through hybridization,breeding precocious and high-quality new walnut varieties has long-term and significant meaning of social,ecological and economic. RAPD were applied to study genetic diversity,genetic structure of inter-population and intra-population for 'Yunxin' walnut(J.sigillata×J.regia),'Sichuan' walnut(J. sigillata) and hybrids F₁.Combined with the heterosis of main shape and quality indicators,the feasibility of using RAPD to prediction the heterosis percentage was disscussed.The main results were as follows:1.Traditional CTAB and improved CTAB methods were used to extract DNA from walnut young leaves,and through agarose gel electrophoresis and ultraviolet absorbance spectrophotometer tested the DNA samples.The later method was more suitable for RAPD analysis which obtained high quality DNA which had a good structural integrity and high molecular weight,with the OD260/OD280 value 1.8～1.9.2.By orthogonal test,the most suitable reaction system(20μL) for walnut DNA of PCR amplification was:10×PCR buffer 2.0μL,dNTPs(2.0mmol/L) 1.8μL,MgCl₂ (25mmol/L) 1.2μL,TaqDNA polymerase(5U/μL) 0.4μL,10 -code primer(2μmol/L) 0.3μL,template DNA(20ng/μL) 1μL.3.RAPD were used to detect the genetic diversity among 28 materials of Juglans, and 26 primers were screened out of 200 random primers.250 DNA fragments which ranged from 200bp to 2100bp were amplified,while the average number of DNA fragments per primer was 9.62.And 181 polymorphic fragments(72.4%) were detected, and the average number of DNA fragments per primer was 6.96.From the analysis of polymorphic loci percentage(P),Nei's genetic diversity(H) and Shannon's information index(I) on three groups,the genetic diversity of hybrid generation F₁ was the highest (P=69.2%,H=0.2771,I=0.4033),followed by the genetic diversity of the female parent(P=41.2%,H=0.1610,I=0.2356),and the paternal genetic diversity was the lowest(P=32.8%,H=0.1280,I=0.1878).4.Based on the analysis of the genetic structural parameters(coefficient of genetic differentiation and gene flow),genetic differentiation coefficient(Gst) of three groups was 0.2370.indicating little genetic differentiation of inter-population,and the genetic variation main existed in intra-population,accounting for 76.3%.AMOVA analysis also showed that inter-population difference was significant(P＜0.001),and genetic variation of intra-population was greater than that of inter-population.The average of gene flow(Nm) estimated indirectly by Gst is 1.6101,indicating that inter-population differentiation had taken place,and there were certain gene flow of inter-population. Controlled-Pollination for walnut's hybrid was the main reason of the gene flow.5.From UPGMA cluster analysis based on the Nei's genetic distance,genetic distance between F₁ and parents was non-equivalent,but biased in favor of the female parent.From the individual point of view,the female parent and male parent were classified two clusters,with 83.3%of F₁ biased in favor of the female parent while 16.7 percent biased in favor of the male.The genetic similarity index and genetic distance for different combinations of hybrid parents were different.6.The correlation analysis between heterosis percentage of 4 nuts quality and genetic distance of parents showed that the genetic distance between parents was negatively correlated with shell thickness,while positively correlated with kernel rate. Correlation coefficient between genetic distance and heterosis percentage of shell thickness was significant(P＜0.05),but the correlation coefficient between the parental genetic distance and heterosis percentage of nut diameter,nut weight was very small. Results of variance analysis showed that variations of shell thickness between hybrids and parents were small and not obvious,suggersting that genetic capacity of shell thickness was very stable,the correlation degree between genetic distance and heterosis percentage varied with different traits.Using RAPD to estimate genetic distance and prediction heterosis percentage of the main quality traits for walnut had important reference value.