| Abundant walnut germplasm resources in Sichuan Province and mature breeding techniques in recent years have greatly improved the number of walnut varieties recognized in Sichuan Province.However,due to the lack of efficient walnut variety identification technology,which is not conducive to the protection of breeders' intellectual property rights,it may lead to the phenomenon of "shoddy" in the walnut seedling trading market,potentially restricting the development of walnut industry.Hence,in this study,SSR markers combined with walnut nut phenotype were used to construct the identification system of Sichuan walnut improved varieties,and cluster analysis was used to explore the genetic relationship between Sichuan walnut improved varieties.The main results are as follows:(1)PCR products of 11 SSR loci of 43 walnut varieties were sequenced by capillary electrophoresis fluorescence labeling detection technology,and 84 alleles were obtained,with an average of 7.6 and good polymorphism.Genetic diversity analysis using GenAlEx 6.5 software showed that the polymorphism information content(PIC)of 11 pairs of SSR primers ranged from 0.564 to 0.803,with an average value of 0.699.The primers were highly informative(PIC>0.5)and were suitable for molecular genetic research of Sichuan walnut resources;Apparent heterozygosity(Ho)is 0.349~0.857(average value: 0.636);The expected heterozygosity(He)is 0.609~0.822(average value: 0.736),and the genetic diversity of improved walnut varieties in Sichuan is rich.(2)The genetic similarity coefficient among 32 common walnut varieties(Juglans regia)is 0.580~0.988.UPGMA cluster analysis showed that 32 walnut varieties were clustered preferentially according to variety types(Sichuan local variety type,hybrid variety type,northern introduction and Yunnan introduction).The clustering results of Sichuan local varieties showed no obvious correlation with geographical sources.(3)The genetic similarity coefficient among 11 walnut cultivars(Juglans sigillata)ranged from 0.525 to 0.932.The results of UPGMA cluster analysis show a certain regional correlation.Taking the lower reaches of Yalong River,Daxiangling and Xiaoxiangling as the boundary,the varieties bred in the areas north and west of the boundary are grouped into one category,which is the natural distribution area of Juglans sigillata;Varieties in the areas east and south of the boundary are grouped into one category,which is the area where the natural distribution of walnuts is in transition to the suitable growth area of common walnuts.The classification status of asbestos megakaryocytes is controversial,and this study tends to classify them as common walnuts.(4)A total of 43 walnut varieties are rich in nut shape characteristics,including 20 characteristics of nut shape in the Walnut Plant Test Guide.In the two classification groups of the shape of the longitudinal section passing through and perpendicular to the suture line,the proportion of broad ellipse shape is the highest,74.4% and 55.8% respectively;.The shape of base and apexperpendicular to suture are the most common in emarginate and rounded,accounting for 36.2% and 46.5% of the total,respectively.A total of 62.7% varieties have prominent nut tips.(5)Four core primers including wga001,wga004,wga070 and zmz22 were used to combine and combine the five characteristics of walnut nuts(along the longitudinal section shape of the suture line,perpendicular to the longitudinal section shape of the suture line,the shape of the fruit shoulder,the shape of the fruit base and the protruding degree of the fruit tip)to successfully construct the identification map of 43 walnut varieties.In conclusion,the combination of SSR marker technology and nut phenotype can be used for identification and genetic diversity analysis of walnut varieties,which can provide reference for identification and selection of improved walnut varieties in Sichuan Province. |
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