Association Analysis And QTL Mapping For Aphid Resistance In Cut Chrysanthemum

Chrysanthemum(Chrysanthemum morifolium Ramat.),one of the ten traditional famous flowers in China and one of the world's four popular cut flowers,is of high ornamental and commercial value.Aphid,Macrosiphoniella sanbourni,injures the chrysanthemum seriously,and has become an important issue to be solved in chrysanthemum production.The only way to solve this problem is to clarify the genetic mechanism of chrysanthemum aphid resistance,and to develop new cultivars resistant to aphid.However,the genetic mechanism governing aphid resistance is thus far not thoroughly investigated in chrysanthemum.This study aimed to characterize the genetic variation of the aphid resistance in a global collection of 80 chrysanthemum entries,to excavate excellent parental aphid resistance materials and to identify the molecular markers for aphid resistance by association mapping;To analyze the genetic mechanism of the resistance to aphid in different hybrid combinations of chrysanthemum,we use the major gene plus polygene mixed inheritance model through the hybridization design of aphid resistance germplasm;Finally,through single marker analysis and QTL mapping based on the genetic linkage maps,study the QTL controlling the chrysanthemum resistance of chrysanthemum.This study revealed the genetic mechanism of chrysanthemum resistance in terms of quantitative genetics and obtained the allelic allelic variation(QTL)and high-resistance parental material of chrysanthemum,which is highly resistant to the genetic improvement of chrysanthemum resistance in the future.The new chrysanthemum varieties have important theoretical and practical significance.The main results are as follows:(1)This study aimed to characterize the genetic variation of the aphid resistance in a global collection of 80 chrysanthemum entries,during summer and autumn under greenhouse condition,and to identify the molecular markers for aphid resistance by association mapping.The performances of aphid resistance,quantified by the average damage index of aphid,was significantly correlated(r=0.93,P<0.01)between two seasons.The coefficients phenotypic and genetic variation was calculated around 26%-27%;and a high magnitude(0.93)of broad-sense heritability,together with a moderate relative genetic advance(68%),was estimated for aphid resistance.By using the MLM model that integrates population structure and kinship matrix as covariates association mapping identified 11 markers related to aphid resistance,with the individually explained phenotypic variation ranging from?11%to?57%.Of the three markers predicted in both seasons,SSR184-1 and E1M5-1 were identified as favorable alleles for aphid resistance.Seven cultivars harboring the two favorable alleles were identified as potential donor parents for future improvement of resistance against aphid.These findings add further understanding of the genetic determination of aphid resistance,and the identified favorable alleles and donor parents open a possibility to produce chrysanthemums with enhanced aphid resistance in future.(2)The aphid resistance traits of;Nongong Xuefeng'×'Monalisa'(NM),'Nongnong Xuefeng'×'QX096'(NQ)and 'Nongong Xuefeng'×'QX098'(NX)shows heterosis in all crosses.The rate of mid-parent heterosis respectively are-30%,-2.28%,and 9.30%respectively.All the cross except the NM cross have positive and negative heterosis,whereas the NM cross expresses positive heterosis for aphid resistance.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.The NM cross fits into B2 mode,and the major gene heritability is 91%;The NQ and NX cross fits into A1 mode,and the major genes heritability is 61%and 62%;The findings confirm that the heterosis and major gene effects vary in different genetic backgrounds.The average mean damage index of the offspring of the same female parent and different male parent combinations had differences,but the difference was not significant and showed a weak paternal effect.More attention should be paid to maternal effects when selecting high photosynthetic efficiency parents which are used for breeding for aphid resistance of chrysanthemum.(3)The chrysanthemum 'Nongong Xuefeng'×'Monalisa' Fi generation was used as the material to carry out anti-convulsive QTL mapping studies by Single marker analysis and the genetic map-based QTL analysis.Single marker analysis identifies a total of 15 SRAP marker loci for aphid resistance,with individually explained contribution ratio ranging between 3.57%?7.68%.The genetic map-based QTL analysis uncovers 4 QTLs underlying aphid resistance,mainly distributing on the X3,X4 and X30 linkage groups of 'Nannong Xuefeng' map and the M9 linkage groups of 'Monalisa' maps,with the phenotypic variation explained by an individual QTL varying between 5.9%?9.38%.The findings dissect the dynamic QTL for aphid resistance,and the identified molecular markers tightly link to aphid resistance will be useful for future molecular marker assistant selection breeding.