| Chrysanthemum(Chrysanthemum morifolium Ramat.),one of the traditional famous flowers in China and the world's popular cut flowers,is of high ornamental and commercial value.In recent years,since the benefit of chrysanthemum is highlighted in urban landscaping and beautiful countryside construction,the demand for new novel varieties is increasing.Crossbreeding is the most efficient approach to developing new chrysanthemums,and understanding the genetic basis of the major horticultural traits is critical to enhanced breeding efficiency in chrysanthemum.With the deepening of chrysanthenmum breeding and as a result of the complex backgrounds,the kwowledge regarding crossbreeding in chrysanthemum cannot meet the demand of modern chrysanthemum breeding research,thus depressing the breeding efficiency.In the present study,eight horticultural traits,i.e.,plant height,stem diameter,leaf length and width,flower diameter,and ray floret number,length and width of twelve F1 progenies derived from a 4 × 3 diallel design(NC?)are investigated in two successive years,with an intention of dissecting the combining ability,heterosis and major gene effect of the horticultural traits in cut chrysanthemum.The findings of this study will add new understanding to genetic determinism of the investigated traits and enrich the breeding knowledge in chrysanthemum.The main results are as follows:(1)Presence of heterosis,though variable among or between crosses and traits,is found generally for the eight traits.'Monalisa White' expresses positive general combining ability(GCA)effects on the eight investigated traits,and QX096,QX097 and 'Nannong Xuefeng'on most of the investigated traits.The special combining ability(SCA)analysis reveals several crosses,i.e.,A1B3?A2B2?A3B1,demonstrating positive SCA effects on most of the investigated traits.High narrow heritabilities in a range of 86.30%?95.24%are estimated for all the eight traits,which were found to be controlled by both additive and non-additive effects.In addtition,maternal inheritance is found for plant height,flower diameter,ray floret length and width,while paternal inheritance for stem diameter,leaf length and width,and ray floret number.The correlation analysis detects a significant correlation between heterosis and SCA effects for leaf width and ray floret width,whereas few significant correlations are estimated between SRAP-based parental genetic distance vs heterosis or combining ability effects.The findings help understand the genetic mechnisms of important traits in chrysanthemum,and guide future parent selection in crossbreeding.(2)Genetic relationship amongst the six cultivars of cut chrysanthemum and their 38 F,hybrids derived from a 2×4 incomplete diallel cross was unraveled by SRAP markers.The SRAP genotyping suggested that of the 229 fragments produced by 17 SRAP primer combinations 127 were polymorphic,with an average of 7.5 polymorphic fragments per primer combination,thus indicative of a moderate molecular diversity present in the entries.The Nei's genetic distances were estimated between 0.11?0.25 and averaged at 0.19,denoting a close genetic relationship among the parental cultivars.The SRAP-based genetic similarity was calculated at 0.42?0.72 and 0.40?0.85,respectively,for the parental cultivars and the F1 hybrids,and the median of genetic similarity(0.61)for the hybrids were higher than that(0.55)for parental cultivars.This suggests a narrowing genetic base or homogenization during hybridization in chrysanthemum,despite the occurrence of some variant lines.Based on genetic similarity matrix,the UPGMA clustering classified the investigated entries into two major groups well congruent with female parents and cross combinations,reinforcing the reliability of SRAP markers in distinguishing F1 hybrids resulted from different combinations in chrysanthemum.(3)The six vegetative traits,i.e.,plant height,stem diameter,leaf length and width,and internode length and number of 'Monalisa White' × 'Hanxiaobai'(MH)and 'Monalisa white' × QX097(MQ)showing constrasting growth potentials are investigated and heterosis are found for all the vegetative traits in both crosses.MH crosses shows positive heterosis for all the traits except internode length,and a relative high mid-parent heterosis effects are found for leaf width,internode number and plant height,with rate of mid-parent heterosis respectively at 16.04%,12.27%,and 11.13%;whereas the MQ cross expresses negative heterosis for all the vegetative traits.The analysis of mixed inheritance model of major gene plus minor gene demonstrates that different inheritance modes are estimated for the traits in different crosses,but all the identified major genes are additive.Plant height of MH cross fits into B3 mode,and the major gene heritability is 97.12%;leaf width and intemode length of MQ cross fit into A2 mode,and the major gene heritability is 68.71%and 70.76%,respectively;leaf length and stem diameter of MQ cross are accorded with B3 mode,with the major gene heritability at 92.79%and 9.33%,respectively;and no major gene is found for other traits.The findings confirm that the heterosis and major gene effects vary in different genetic backgrounds.(4)By investigating the stem related traits,i.e.,plant height,stem diameter,and internode number of the cut-chrysanthemum crosses `Monalisa White' x 'Hanxiaobai'(MH)and 'Monalisa White' x Qx097(MQ)with contrasting segregating patterns at 15,30,45,60,and 75 days after planting,the present study was set up to dissect the growth dynamics,heterosis and major gene effect of stem traits in chrysanthemum.The results showed that the stem traits of the two crosses expressed a similar dynamic growth trend,likely not affected by the difference of the parent performance on these traits.The accumulative growth curve shaped like S-type for plant height and stem diameter rather than internode length,and the relative growth rate for all stem traits increased relatively higher within 45 days after planting.The averages of all stem traits in MQ cross were higher than in MH cross at most investigated stages,while the coefficients of variations of plant height and internode number in MH cross were higher than in MQ cross at every investigated stage,with no clear pattern found for stem diameter.The stem traits demonstrated a positive mid-parent heterosis rate at most investigated stages in MH cross,whereas a negative heterosis rate was estimated for all stem traits at every investigated stage except stem diameter at 15 days after planting,thus indicating a significant correlation between the performance of heterosis and the heterogeneity of the parents. |
PDF Full Text Request