| Chrysanthemum(Chrysanthemum morifolium Ramat.)is one of ten famous traditional flowers in China and one of the four leading cut flowers in the world,thus possessing high ornamental and economic values.Drought stress is one of the important abiotic stress factors that limit palnt growth and yield.Understanding the genetic model of drought resistance is crucial to its breeding improvement.Due to the narrow genetic base of cultivated chrysanthemum,it is difficult to improve resistance traits by intracutlivar hybridization.However,our country possess abundant chryanthemum related wild species or genera sharing many important resistance or ornamental traits,and distant hybridization proves to be an efficient way of transferring the important traits into cutlivated chyrsanthemum.Recently,the utilization of wild species with low ploidy is becoming an important point in chrysanthemum germplasm innovation.Whereas,few researches focus on the genetic pattern in chrysanthemum related species,and whether reciprocal hybridization brings about genetic difference remains unknow.In this study,we took the interspecific reciprocal F1 progenies derived from C.dichrum and C.nankingense as materials,and compared the genetic difference by SRAP markers,horticultral traits and drought tolerance-related traits,and finally created some excellent materials for future use in chrysnthemum breeding activities.The main results are as follows:(1)The hybrid authenticity and genetic diversity of the reciprocal F1 progenies derived from C.dichrum and C.nankingense were studied using SRAP markers and morphological traits.The results showed that the 271 hybrid F1 generations were all true hybrids with hybrid authenticity rate 100%.The 24 pairs of SRAP primers amplified 303 polymorphic bands with 13 polymorphic bands per pair of primers amplified on average.The genetic similarity coefficient of C.dichrum and C.nankingense was 0.45,indicating that the genetic relationship is relatively distant.The UPGMA cluster analysis divided the parent and 175 hybrids of C.dichrum × C.nankingense into 6 categories at the genetic similarity coefficient of 0.60,and 40%of the hybrids were clustered together with the female parent C.dichrum.At the genetic similarity coefficient of 0.62,the parents and the hybrids of C.nankingense ×C.dichrum were divided into 4 categories,and 33.33%hybrids were clustered with the female parent C.nankingense,while the male parents of the reciprocal crosses were grouped together separately.Eight of 12 investigated horticultural traits showed significant difference(P<0.01)between the reciprocal crosses.Results of the morphological traits-based clustering confirm that most hybrids were grouped with the corresponding female parent,pointing the presence of partial maternal inheritance.(2)The variation of the 12 leaf-and flower-related traits,i.e.,leaf length,leaf width,leaf length/leaf width,leaf area,petiole length,leaf tooth number,flower diameter,center flower diameter,ray floret length,ray floret width,ray floret number and tubular floret number was analyzed using major gene plus polygene mixed inheritance model.The results showed that the coefficients of variation of the 12 traits in the reciprocal progenies ranged in 8.81%～30.09%and 10.46%～55.78%,respectively.Heterosis ratio of the 12 traits varied in a range of-1.39%～53.02%and-13.21%～108.84%,most of which reached significance at 0.01 level.There were 26 and 37 significant pair-wise correlation(P<0.01)were observed in the reciprocal F1 progenies.Mixed genetic analysis showed that no major gene were detected for leaf tooth number,and different geneitc models were detected for leaf length,leaf width,leaf area,tubular floret number in the reciprocal F1 progenies;in addition,leaf length/leaf width,petiole length,flower diameter,center flower diameter,ray floret length,ray floret width,and ray floret number were all governed by B1 model,but the reciprocal F1 populations differed largely in genetic parameters of the former mentioned traits.Thus,leaf-and flower-related traits show genetic difference in the reciprocal F1 populations,and we should take the effect of reciprocal crosses into consideration in future breeding program involving with those wild species.(3)The drought tolerance in the reciprocal progenies of C.dichrum and C.nankingense were evaluated based on nine drought tolerance component traits,i.e.,wilting index,plant height,root length,fresh root weight,fresh shoot weight,root dry weight,shoot dry weight,fresh weight root/shoot ratio,dry weight root/shoot ratio,and the genetic difference were investigated.The results showed that dought stress caused a significant(P<0.01)variation of the nine investigated traits in the reciprocal progenies,and the stress index varied in a wide range,of which fresh weight root/shoot ratio show relatively large coefficient of variation 37.88%and 36.76 in the reciprocal progenies,and wilting index show largest coeffecient of variation 39.44%in C.nankingense ×C.dichrum.Principal component analysis extracted two principal components from the nine drought resistance indicators,which explained larger than 70%of the phenotypic variation.Comprehensive evaluation divided the reciprocal progenies into five categories:high drought resistance,drought resistance,low drought resistance,non-drought resistance and extremely non-drought resistance.There are 7 hybrid lines with higher drought resistance than resistant parent C.dichrum,namely Y80,Y38,Y66,Y59,Y65,Y34 in C.dichrum ×C.nankingense and J51 in C.nankingense ×C.dichrum.The major gene plus polygene mixed inheritance model analysis obvered that the drought resistance in the reciprocal F1 progenies was controlled by an pair of major genes with additive-dominant effect,and the heritability of the major genes of reciprocal crosses was 50.02%and 50.49%,respectively.The findings This study is the genetic improvement and drought resistance QTL mapping of chrysanthemum provided important basis for germplasm innovation and genetic breeding with emphasis on drought tolerance in chrysanthemum. |
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