Germplasm Diversity Of Michelia Macclurei Dandy In Guangxi

Michelia macclurei Dandy is an important rare tree species native to Guangxi Zhuang Autonomous Rigion with multifunctional benefits,such as timber and ornamental value,etc.In view of the fact that utilization of seed was confused,seedling quality was uneven and promotion of planting was limited due to the lack of systematically investigation and analysis on germplasm resources status quo of Michelia macclurei in Guangxi,variation and diversity on germplasm of Michelia macclurei were systematically studied from aspects of phenotype of parental tree,phenotype and germination characteristics of seed,growth and physiology as well as resistance to insect of seedling,and AFLP molecular marker,basing on the materials of the parental trees,seeds and their seedlings of the existing 8 natural populations in Guangxi aiming to provide theoretical basis for collection,preservation,evaluation,breeding and utilization of germplasm resources of Michelia macclurei in Guangxi,and promote cultivation of the fine germplasm resources of Michelia macclurei.The main results from this study are summarized as follows:(1)There were abundant phenotypic variations in Michelia macclurei in Guangxi.Among the 24 tested phenotypic traits,18 were extremely significantly different(p<0.01)among populations,namely,fullness of stem(TR),straightness of stem(TS),length of leaf(LL),width of leaf(LW),petiole length of leaf(PL),length of seed(SL),width of seed(SW),thickness of seed(ST),thousand grain weight of seed(TSK),water content of seed(WC),days for radicle emergence(DSG),days for cotyledon unfolding(DC),days for the first true leaf unfolding(DL),germination rate(GR),length of axial root(RL),length of hypocotyl(HL),length of cotyledon(CL)and width of cotyledon(CW),which indicated that there were rich variations among populations.Average coefficients of variation within and among populations for 10 traits,for example,HL,were 19.3%and 12.1%,respectively,variation within population was richer than that among populations;however,average coefficients of variation within and among populations for other 6 traits,for example,TR,were 9.6%and 15.0%,respectively,variation within population was less than that among populations.Average diversity indexes within and among populations were 1.184 and 1.537,respectively,in general,diversities of phenotypic traits within population were lower than that among populations.(2)There were obvious differences in seedling growth among natural populations of Michelia macclurei.Extremely significant differences(p<0.01)or significant differences(p<0.05)in height and ground diameter of seedling among populations were found in most months.In December of the year of seedling transplantation,coefficients of variation among populations were 9.7%for height and 8.8%for ground diameter,and average coefficients of variation within population were 8.5%for height and 5.2%for ground diameter,variations of these 2 traits among populations were richer than that within population.Diversity indexes among populations were 1.464 for height and1.439 for ground diameter,respectively.The highest selection rate of super seedling based on average ground diameter as well as average height and ground diameter all appeared in population BBDP-1.(3)There were dramatic differences in many physiological traits about photosynthesis of Michelia macclurei seedling from different natural populations.Extremely significant differences(p<0.01)or significant differences(p<0.05)were found in 5 of 9 physiological traits of seedling among populations,including net photosynthetic rate(PR),chlorophyll a content(CCa),chlorophyll b content(CCb),total chlorophyll content(CCT),stoma density(SD).Great differences among populations in these 4 traits,namely,stomatal conductance(SC),intercellular CO₂concentration(ICC),transpiration consumption rate of water(CRW)and ratio of chlorophyll a to chlorophyll b(RCC)were also found.The average value of diversity index among populations of 9 physiological traits was 1.502,showing a high level of diversity.(4)Remarkable differences in seedling resistance to insect(Graphium agamemnon)among natural populations of Michelia macclurei were detected.There were extremely significant differences(p<0.01)in both number of seedling attacked by Graphium agamemnon larva(SS)and number of larva of Graphium agamemnon(SN)among populations.Variations of SS(CV_B=70.1%)and SN(CV_B=73.6%)among populations were all great,among all populations,BBDD-1 was the slightest in terms of seedling attacked by Graphium agamemnon.SS and SN had the same average value of 1.561 for diversity index among populations in 2 years.(5)Correlation analysis of tested traits of Michelia macclurei showed that CCb was significantly(p<0.05)positively correlated with HL;LL,LW,SL,SW,TSK,DSG,DC were extremely significantly(p<0.01)or significantly negatively correlated with SS and SN respectively;H was significantly negatively correlated with GR.Longitude,latitude and elevation were significantly positively or negatively correlated with SS and SN respectively;longitude was extremely significantly positively correlated with RL and significantly negatively correlated with CL;there was a significantly negatively correlation between elevation and TSK.(6)Principal component analysis indicated that phenotype of parental tree,phenotype and germination of seed,growth,physiology and resistance to insect of seedling from 8 natural populations of Michelia macclurei had their own characteristics.Accumulative contribution rate of the first three principal components was up to67.82%,totally 22 traits contributed to these 3 principal components,such as TR,LL,SL,DSG,CL,PR,etc.Population BBDP-1 was better in TR and TS,greater in PL,SL,SW,and ground diameter of seedling;population BBJN-2 was better in TR,higher in PR,ground diameter and height of seedling;population BBDD-1 and BBDD-2 had bigger values of LL and LW,slower germination speed,longer HL;population BBJN-1had lower resistance to insect;population PBDC-1 was higher in SD.(7)Genetic diversity analysis based on AFLP markers showed that the average ratio of polymorphic band of Michelia macclurei from natural populations was up to41.94%,average Nei's genetic diversity index(H)and shannon's index(I)were 0.129and 0.199,respectively.Among all populations,BBDD-1(H=0.142,I=0.221)and PBDC-1(H=0.141,I=0.217)presented relatively high level of genetic diversity.Genetic variation within and among populations accounted for 71%and 29%,respectively,revealing that the genetic variation mainly existed within population,which was consistent with the results of phenotypic trait analysis.(8)Results of cluster analysis indicated that the 8 natural populations of Michelia macclurei were all clustered into 3 groups based on both phenotypic trait and molecular genetic distance,but the results were not completely the same,possibly because of some phenotypic traits were greatly affected by the environment,which made deviations in phenotypic clustering results.Looking at geographic distance and genetic distance between populations,although some of the geographically nearer populations were clustered into a group,populations were not isolated by distance,probably due to some of the tested populations were strongly disturbed by human activities.In conclusion,the natural populations and their progenies of Michelia macclurei in Guangxi had abundant variations in many phenotypic,physiological and insect resistant traits.At the same time,the analysis of population genetic diversity showed that there was high genetic diversity among and within populations,which indicates that the wild resources of Michelia macclurei in Guangxi have great potential for collection and genetic breeding.Based on phenotype and genetic distance,the germplasm resources of Michelia macclurei in Guangxi can be roughly divided into three groups.The results provide an important reference for the collection,management and utilization of Michelia macclurei germplasm resources in Guangxi.