Aroma Volatiles Analysis And QTL Mapping In The F₁ Progeny Fruits Of ‘Honeycrisp’ × ‘Qinguan’ Apple Cross

Aroma is an important attribute of apple fruit quality.Fruit aroma,a complex trait controlled by multiple genes,is closely related to genetic factors and environmental factors.QTL mapping based on the linkage map is the major method to study quantitative traits in plants.In this study,the F₁ progeny fruits（2014-2016）of‘Honeycrisp’בQinguan’were used as experimental materials.Fruit aroma volatiles content and distribution characteristics were analyzed by gas chromatography-mass spectrometry.Based on the established SNP map,QTL mapping for fruit aroma volatiles was carried out to obtaining the stable genetic QTLs.These will lay foundations for understanding molecular mechanisms of apple fruit aroma volatiles synthesis.The main results are presented as follows:1.Aroma volatiles in the F₁ progeny fruits of‘Honeycrisp’בQinguan’were analyzed based on standard substances,using gas chromatography-mass spectrometry.A total of 42aroma volatiles were detected in F₁ fruits,including 21 esters,5 alcohols,7 aldehydes,4organic acids,2 benzene series and 3 terpenes.In F1 progeny fruits,the number of esters was the richest,among which hexyl acetate had the highest average content.The same as,the content of aldehydes was the most abundant,and C₆ aldehydes were the main components.2.The distribution of different aroma volatiles in F₁ progeny fruits of‘Honeycrisp’בQinguan’was different,showing different genetic patterns.The content of twenty-four volatiles showed continuously skewed distribution to the lower value,including hexyl acetate,hexyl hexanoate,hexanol,hexanal,and so on.The content of eighteen volatiles showed discrete distribution and complied with Mendelian inheritance,including ethyl butyrate（1:3）,E,E-2,4-hexadienal（1:3）and estragole（1:1）and excluding butyl2-methylbutyrate and 1,3-Octanediol.3.The correlation analysis of aromas in F₁ progeny fruits of‘Honeycrisp’בQinguan’showed that,pentyl 2-methylbutyrate had significant positive correlation with pentyl pentanoate in 2014-2016（r≥0.85）.There were also significant positive correlations between butyl 2-methylbutyrate and pentyl 2-methylbutyrate（r≥0.82）,and between hexyl hexanoate and hexyl caprylate（r≥0.89）in 2014-2015.Results of cluster analysis showed that,42 aromas were clustered into four groups.Group A was dominated by esters other than ethyl esters and alcohols,and this group could be subdivided into two subgroups including branched esters and linear esters,respectively.Group B was mainly ethyl ester.Group C was dominated by aldehydes and terpenes.And the others volatiles failed into group D.4.QTL mapping for fruit aromas was carried out based on the SNP genetic linkage map of‘Honeycrisp’בQinguan’.A total of 569 QTLs related to fruit aromas were obtained,including 82 stable genetic loci.They were located in 12 linkage groups of LG1,2,3,4,5,6,8,10,12,13,15 and 16,respectively.The QTLs of some correlations and clustered aroma substances overlapped or linked.The QTLs of 2-methyl butyl acetate,hexyl acetate,ethyl butyrate,propyl butyrate,pentyl acetate,ethyl hexanoate,hexyl 2-methylpropionate,hexyl caprylate,E-2-hexenal,α-farnesene and estragole were interlinked and located at LG3.Butyl2-methyl butyrate,pentyl 2-methyl butyrate and 2-methylbutyric acid were co-located at LG5.