| Drought is an important abiotic stress that adversely affects growth and yield of chrysanthemum(Chrysanthemum morifolium Ramat.),and it is necessary to understand the genetic model of target traits for genetic improvement.The complex background,i.e.,hexaploid(2n=6x=54)and sometimes many forms of aneuploidy,genetic complexity,high heterozygosity and self-incompatibility of cultivated chrysanthemum hinder the progress of genetic improvement for most traits including drought tolerance.Chrysanthemum originates in China where have diversified Chrysanthemum related species and especially the utilization of diploid species will facilitate dissecting genetic mechanisms of traits in chrysanthemum.In order to better understand the genetics of drought tolerance and other horticultural traits,the present study set out to examine hybrid authenticity and genetic diversity of interspecific C.nankingense X C.lavandulifolium F1 population by using molecular markers(SSR and SRAP)and morphological traits and to unravel the genetic pattern of some horticultural traits and drought tolerance in the segregating interspecific F1 population using the mixed genetic model of major gene and polygene.The findings of the current study will make clear the genetic variation of drought tolerance in interspecific C.nankingense × C.lavandulifolium F1 progenies and screen out some elite breeding materials with improved drought tolerance,and shed light on future genetic dissection by QTL mapping for drought tolerance in cultivated chrysanthemum.The main results are as follows:1.Three pairs of primers with paternal specific bands were screened out from 42 pairs of SSR primer combinations and 18 pairs of SRAP primer combinations.103,87 and 69 offspring with paternal specific bands were detected by SRAP primer M2E13,M16E19 and SSR primer 187,respectively.According to the amplification results of three pairs of primers,122 of 131 F1 hybrids were true hybrids,and the true hybrids rate was 93.13%.There were 123 polymorphic bands amplified by 42 pairs of SSR primer combinations in C.nankingense,C.lavandulifolium and 122 F1 hybrids,with an average of 3 polymorphic bands amplified by each pair of primers;55 polymorphic bands were amplified by 18 pairs of SRAP primer combinations,with an average of 3 polymorphic bands amplified by each pair of primers.The genetic similarity coefficient of F1 hybrids between C.nankingense and C.lavandulifolium was between 0.44 and 0.90,and the average genetic similarity coefficient was 0.58.The average coefficient of genetic similarity between maternal and interspecific hybrids(0.62)was higher than that of male parent(0.54).UPGMA cluster analysis based on SSR and SRAP molecular markers classified parents and 122 hybrid progenies into 7 groups.Most of the hybrid progenies were clustered with the female parent C.nankingense,while the male parent C.lavandulifolium and a few hybrid lines were clustered separately,which indicated that F1 hybrids was more similar to the female parent and had a longer genetic distance from the male parent.2.Variations of phenotypic traits in C.nankingense × C.lavandulifolium F1 population were abundant,with the coefficient of variation ranging from 10.16%to 16.67%.The heterosis of 9 phenotypic traits reached an extreme significance at P<0.01 level.The phenomena of transgressive segregation existed in all traits of hybrid progenies,among which ray floret number,ray floret width,tubular floret number,and center flower diameter formed the transgressive heterosis.The correlation analysis of the traits of offspring showed that 25 of the 45 traits were significantly correlated,most of which were highly significant positive correlated.UPGMA clustering classifies the two parents and 122 interspecific hybrids into 7 groups.Most of the hybrid progenies are clustered with the female parent C.nankingense.The clustering results show that the hybrid progenies are more similar to the female parent in phenotype.Mixed genetic analysis showed that plant height accorded with A-1 model,showing an additive-dominant effect controlled by a pair of major genes.The remaining traits accorded with B-1 model,showing an additive-dominant-epistatic effect controlled by two pairs of major genes.The heritability of major genes ranged from 67.27%to 99.65%.3.Drought tolerance of C.nankingense,C.lavandulifolium and their 122 hybrid progenies was examined by the method of withholding water.The results showed that the drought treatment caused a significant effect on the morphological traits and drought resistance index varied widely among different lines among which fresh weight stress index showed the largest variation.Drought tolerance traits showed different degrees of correlation.Principal component analysis was used to extract three principal components from nine stress indices,with the cumulative contribution rate up to 72.49%.Fresh shoot weight,fresh root weight,fresh shoot weight,root dry weight,plant height,and wilting index had a greater impact on drought tolerance,indicating that they were closely related to drought resistance.Principal component analysis and subordinate function method were used to evaluate the drought resistance of parents and offspring at cuttage seedling stage.The F1 hybrids were divided into five categories:extremely drought-sensitive,drought-sensitive,low drought-resistant,drought-resistant,and high drought-resistant,which included 21,57,39,6 and 1 lines,respectively.The genetic analysis of major gene plus polygene mixed inheritance model indicated that drought resistance was controlled by two pairs of main genes with additive-dominant inheritance rate of 43.9%.This study revealed an abundant variation of drought tolerance and identified excellent materials with improved drought tolerance for future parental selection in crossbreeding,and shed light on the future QTL mapping for drought tolerance of chrysanthemum. |
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