| Chinese cabbage (Brassica campestris L. ssp. Pekinensis (Lour) Olsson), one of the major vegetables originates from China, plays an important role in supply of China vegetable market. In recent years, much progress has been made on its quality study. However, few reports were found on the quantitative analysis of volatile components and no reports on effects of its chewy degree. In order to develop a aroma evaluation system and provide scientific proof for high-quality breeding in Chinese cabbage, twelve cultivars including'Shandong No.7','Xibai No.4','87114','Qing Za Zhong Feng', and their parents, respectively, were used to study the volatile components. Moreover, sixteen capsicum combinations were made with four Chinese cabbage inbred lines, i. e.'Hua273','114 Fushan','114Chengyangqing'and'Weigu', by complete diallel crossing to study the effects on chewy degree, the genetic parameters of major volatile components and factors correlated with chewy degree of Chinese cabbage. The results were as following:1.Volatile components of twelve Chinese cabbage materials including'Shandong No.7','Xibai No.4','87114','Qingzazhongfeng'and their parents, were analyzed by head space-solid phase microextration and Gas Chromatography-Mass Spectrometry (GC-MS). The identification and quantification of volatile compounds were performed at a Finnigan Trace MS using a polyethylene glycol (PEG) capillary column (30 m×0.25 mm×0.25μm), and a Carboxen-polydimethylsiloxane (CAR-PDMS) 100μm extraction fibers were used. Helium was used as the carrier gas; the flow rate of the mobile phase was 1 ml·min-1. The initial oven temperature was 35℃, held for 3 min, ramped at 8℃·min-1 to 45℃, then ramped at 6℃·min-1 to 140℃, and ramped at 10℃·min-1 to 230℃and held for 6 min. The mass spectrometer was operated in the electron ionization mode at 70 eV, a source temperature of 200℃, interface temperature of 250℃. The detector voltage for MS was 350 V, and the filament emission current was 200μA.More than 170 compounds belonging to 14 varieties via GC-MS were identified. The majority of compounds detected in Chinese cabbage were nitrile, esters, aldehydes, ketones, alcohols, hydrocarbons and heterocycles. Even the volatile components were complex and varied greatly in different years, 2-cyclohexen-1-ol, 2-hexenal, 3-hexen-1-ol(Z/E), benzene, (2-isothiocyanatoethyl) and benzenepropanenitrile were always detected with relatively high content and considered as the characteristic aroma volatiles of Chinese cabbage.In the two-year trails, 45 compounds could be detected in both years. Principal component analysis was made on those major components according to their relative content. Seven aroma compounds, e.g. 2-penten-ol, hexanenitrile, 2,4-hexadienal, hexanenitrile, 5-methyl, 2-hexenoic acid, thiocyanic methyl ester and 2,4-heptadienal(E,E), were determined to be the major compounds affecting Chinese cabbage flavor based on the criteria that accumulative variance reached over 85%.2. Sixteen capsicum combinations were made with four Chinese cabbage inbred lines including'Hua273','114Fushan','114Chengyangqing'and'Weigu'by complete diallel crossing. Genetic analysis of major volatile components was studied using Zhujun's (1997) additive-dominant-maternal model and the MINQUE method. The results showed that 1-hexanol, 2,4-hexadienal , hexanenitrile, 5-methyl, 2-hexenoic acid and 2,4-heptadienal(E,E) were controlled by additive-dominant-maternal effects, while 2-penten-ol and thiocyanic methyl ester were controlled by the additive-dominance effect.The narrow sense heritability of these seven major compounds reached an extremely significant level, indicating that generation selection of parental lines and parent selection were effective to these traits. Therefore genetic improvement could be applied for these traits in the early generations. Due to high residue variance, hexanenitrile, hexanenitrile, 5-methyl, 2-hexenoic acid and 2,4-heptadienal (E,E) could not be selected in the early generations, however selection on high generations would be appropriate. Moreover, the broad sense heritability was significantly higher than their narrow sense heritability, showing that the dominance effects were significant. These indicated that they were suitable for heterosis breeding.The correlation analysis among volatile components revealed that there were significant negative correlations among the contents of nitriles and no significant correlations among the contents of aldehydes. As to other pairs of aroma compounds, there were significant positive correlations.3. Six Chinese cabbage materials were used to study the effects of agronomic traits, cell wall components and correlated enzymes on chewy degree. The testing materials included two easy-chewed cultivars ('114Chengyangqing'and'Hua273×114 Chengyangqing'), two hard-chewy cultivars ('114Fushan'and'Weigu'), and two middle-chewy cultivars ('114Fushan×114Chengyangqing'and'Weigu×114Fushan'). The results showed that there were extremely significant or significant negative correlations between chewy degree and dry matter content, proto pectin (PP) content, and PP/TP (total pectin). There were significant or extremely significant positive correlations between chewy degree and WSP (water soluble pectin) /PP, PG activity. As of these correlations, we could evaluate chewy degree of Chinese cabbage by dry matter content, PP content or WSP/PP.4. Sixteen capsicum combinations were made with four Chinese cabbage inbred lines including'Hua273','114Fushan','114Chengyangqing'and'Weigu'by complete diallel crossing. Genetic analysis of dry matter content, WSP content, PP content, TP content and WSP/TP ratio was studied using Zhujun's additive-dominant- maternal model. The results showed that dry matter content was controlled by additive-dominance effect, while WSP/TP was controlled by additive-dominant- maternal effects, and WSP content was controlled by additive and maternal effects. To these three traits, the additive effects were more important than other effects. But to PP content and TP content, dominance effects were more important. The narrow sense heritability of dry matter content, WSP content, WSP/TP reached an extremely significant level.The correlation analysis revealed that there were significant positive correlations between the contents of dry matter and PP content (r =0.441; P< 0.01), and highly significant correlation between the contents of PP content and WSP content.5. An F2 population from'Hua273'and'114Fushan'hybridization was used to study the molecular marker linked to chewy degree of Chinese cabbage via RAPD technique. The optimal PCR system for RAPD analysis was as follows: 60 ng template DNA, 1.5 mmol·L-1 Mgcl2, 200μmol·L-1 dNTP, 0.4μmol·L-1 primer, 1 unit Taq DNA polymerase.By BSA method, 1621 electrophoretic bands were analyzed with 264 primers, and there were 6.14 bands per primer. Of 14 polymorphic primers, OPA06-1400 was identified to be linked with chewy degree gene of Chinese cabbage. The genetic distance between the chewy degree gene and the RAPD marker was 24.8 cM.
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