Growth Adaptability And Genetic Diversity Of Germplasm Resources Of Liriodendron Chinense

Liriodendron chinense(Hemsl.)Sarg.is a national second-class endangered tree species,and it is also an excellent timber and landscaping tree species.It is of great significance to carry out germplasm resources evaluation and excellent germplasm breeding for the conservation and development of L.chinense.In this study,15-year-old L.chinense provenance experimental forest planted in the southern margin of L.chinense natural distribution area(Quanzhou,Guangxi)was used to evaluate the growth adaptability and genetic diversity of 15 provenance based on SSR markers;The core breeding population was established both from the excellent genotypes selected from the provenance trials and some excellent genotypes collected from the origin of excellent provenance,and its seedling growth adaptability(grafting survival rate,seedling growth and leaf phenotype)and genetic diversity(KASP-SNP and SSR)were evaluated.The main results are as follows:(1)There were great differences in growth adaptability among different provenances,which was obviously affected by longitude and latitude,temperature and humidity of provenance.The analysis of variance showed that there were significant differences in growth traits(tree height,DBH,volume and resistance)among provenances.Contingency table test showed a highly significant difference in the preservation rate among provenances(χ2=51.021,p<0.001).Correlation analysis showed that DBH and tree height were significantly negatively correlated with longitude(R2=0.421,p=0.005;R2=0.326,p=0.015)and latitude(R2=0.424,p=0.005;R2=0.319,p=0.017)of provenance sites.Significant positive correlations were observed between DBH and annual extreme minimum temperature(R2=0.265,p=0.029),tree height and annual mean relative humidity(R2=0.339,p=0.013),respectively;BLUP analysis indicated that the provenances from Jinping in Yunnan province and Liping in Guizhou province had higher comprehensive breeding values and better genetic performance in the test sites,which can be used as the preferred area for the collection of L.chinense genetic resources in Guangxi.(2)Based on 20 SSR loci,it revealed that the provenance test forest possessed a high genetic diversity.The average values of observed allele number(Na),allele richness(Ar),Shannon diversity index(H),allele evenness(E),observed heterozygosity(Ho)and expected heterozygosity(He)across 15 provenances were 8.73,6.22,1.69,0.72,0.83 and 0.72,respectively.Most of the SSR loci(82.67%)significantly deviated from the Hardy-Weinberg equilibrium within the provenance(p<0.05),implying that non-random mating commonly occurred in L.chinense population.AMOVA showed that the variation among provenances was 10.74%.The test of IBD(isolation by distance)showed an extremely significant positive correlation between genetic distance and geographical distance among provenances(R2=0.171,p<0.001).The analysis of population co-ancestry(genetic structure)showed that the provenances could be divided into 4 groups(K=4),and among them,Jinping in Yunnan is highly differentiated from other provenances.Lichuan in Hubei,Chengbu in Hunan,Changsha in Hunan and Zherong in Fujian possessed higher common ancestry;followed by Liping in Guizhou,Nanchang in Jiangxi,Lushan in Jiangxi,Xiuning in Anhui,Wuyi Mountain in Fujian,Anji in Zhejiang and Lishui in Zhejiang;as well as Huanjiang in Guangxi,Hefeng in Hubei and Songyang in Zhejiang.(3)Based on growth performance of the provenance trials,89 excellent genotypes(including 50 superior trees from provenance trials,26 superior trees from the origin of superior provenance and 13 L.sino-americanum)were grafted to form a fine core breeding population.Analysis of its growth adaptability at seedling stage showed that there were significant differences in grafting survival rate(χ2=67.515,p<0.001)and seedling height growth(F=243.2,p<0.001)among superior trees from different sources.Rich phenotypic variation of leaves of superior trees from different sources mainly reflected in the depth of top depression and side depression.The results of PCA(principal component analysis)showed that the leaf size and the cracking degree of leaves were the main factors for the variation among provenances.Cluster analysis also exhibited that the leaf phenotypes of L.sino-americanum,Jinping and Malipo provenances were significantly different from other provenances.(4)Based on 20 SSR markers and 17 SNP loci selected from the differential genes of L.chinense and L.sino-americanum,the genetic diversity of the core breeding population was analyzed in the study.The SSR-based genetic diversity of core breeding population was significantly higher than that of provenance trials(p<0.05).The clustering results based on SNP markers were significantly different from those based on SSR markers,suggesting that the two groups of markers were subjected to completely different selection effects.SNP-based individual heterozygosity was significantly positively correlated with DBH growth(R2=0.262,p<0.001),while not with height growth(R2=0.069,p=0.07),which presenting an increasing trend,still.Besides,no significant correlation was observed between SSR-based individual heterozygosity and tree height and DBH phenotype.It indicated that significant correlation was obvious between SNP loci and the growth of L.chinense.In conclusion,the study revealed the adaptability of L.chinense in its southern margin of natural distribution area,and a number of germplasm with superior growth performance were selected and bred,which provides an important reference for the conservation and utilization of L.chinense genetic resources.