| Chrysanthemum(Chrysanthemum morifolium),among the ten traditional famous flowers in China and the four leading cut-flowers worldwide,is of great ornamental and commercial values.Low temperature is one of the major abiotic stresses that adversely affect growth and year-around production of chrysanthemum,so to develop new cultivars with enhanced cold tolerance is an important approach to solving th problem.However,the genetic mechanism govering cold tolerance is rarely investigated in chrysanthemum.In the present study,the genetic variability,heterosis and major gene effect of cold tolerance are investigated in the F1 progeny derived from a cross between a strong cold-tolerant cultivar'Nannong Xuefeng' and a low cold-tolerant cultivar 'Monalisa' at seedling,budding,flowering and rhizome stages,and from a view of molecular quantitative genetics,the QTLs controlling cold toleranc at different growth stages were dissected in the interest of identifying the dynamic modes of the cold tolerance QTLs.The main results are as follows:1.The coefficients of variation(CV)for cold tolerance range from 22.17%to 46.14%at the four growth stages,and the phenomena of heterosis and extra-parent segregation existed widely for cold tolerance in the Fi progeny.The mixed genetic analysis suggested that cold tolerance was fitting into B-1 model,governed by two pair of major genes expressing additivity-dominance-epistasis effect,and the heritability of major gene was,respectively,88.56%and 65.86%at Seeding stage and flowering stage;whereas,few major gene is detected for cold tolerance at bot budding and rhizome stages.The results help understand the genetic variation and major gene effect of cold tolerance at different growth stages,and provide an important guide for future efficient crossbreeding program targeting cold tolerance in chrysanthemum.2.The LT50 of ray florets is-5.37 and-2.2 ?,respectively,for 'Nannong Xuefeng'and 'Monalisa White',and that of the F1 progeny varies between-8.92 ? and 1.31 ?,with a mean of-4.61 ?,thus to an extent suggesting the presence of maternal inheritance for cold tolerance.The cold tolerance of the F1 progeny fits basically into a normal distribution and the CV is 43.60%,confirming its quantitative nature.No major gene effect is detected for cold tolerance of ray florets at flowering stage.The Pearson correlatin analysis reveals a significant positive correlation between cold tolerance of ray florets and flowering time.The findings unravel the genetic variability of cold tolerance of ray folorets,and lay a foundation for later breeding program.3.Single marker analysis identifies a total of 97 SRAP marker loci for cold tolerance at the four growth stages,with individually explained contribution ratio ranging between 4.32%?14.99%.The genetic map-based QTL analysis uncovers 15 QTLs underlying cold tolerance at all the growth stages,mainly distributing on the X1,X11 and X19 linkage groups of 'Nannong Xuefeng' map and the M12,M22 and M33 linkage groups of'Monalisa White' maps,with the phenotypic variation explained by an individual QTL varying between 6.47%?68.89%.Of the 15 QTL,three cluster QTLs harboring on X4,X9,M12 and M3 3 linkage groups are simultaneously responsible for cold tolerance at more than two stages,and moreover,the qBdsCTM33 and qFfsCTM33 that govern cold tolerance respectively at budding and flowering stages on M33 linkage group should be major genes,in the light of their high explained variations of 65.78%and 68.89%.The findings dissect the dynamic QTL for cold tolerance at different growth stages,and the identified molecular markers tightly link to cold tolerance will be useful for future molecular marker assistant selection breeding. |
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