| Blueberry belongs to the genus Vaccinium of family Ericaceae, and has recently received much attention as blueberries have high contents of anthocyanins, flavonols, procyanidins and other types of phenolic compounds, which can improve night vision, provide anti-cancer activity and reduce the risk of heart disease. The taste quality greatly depends on both the content and composition of sugars and acids but also on individual sugar and acid content that are well correlated with fruit flavor characteristics such as sweetness and sourness, these are important factors in the evaluation of fruit quality and selection of a new cultivar. At present, crossbreeding is the general strategy for developing new cultivars in blueberry, it is important to know well the component of sugars and acids and acquire inheritance information when choosing the parents in crossbreeding. In present study, the main sugar and acid component in mature blueberry fruit, including sucrose, glucose, citrate acid and tartaric acid were analyzed in four cross populations in two successive years to study the inheritance of sugars and acids using four cross combinations. A progeny with 94 individuals derived from south highbush blueberry ’Sapphire’ and north highbush blueberry ’Berkeley’ was used as plant materials to construct genetic linkage map. Sugar and acid content were measured by HPLC, and QTL mapping for sugar and acid traits were studied by inclusive composite interval mapping (ICIM). The main results are as follows:1. Glucose and fructose were the main sugar components in matured fruit of blueberry, the content increased during fruit maturation and the contents of them accounted for 97.90%-99.47% of total sugarcontent, the ratio of them was 1:1.Citric acid was the main organic acid, accounted for 76.94% of total acid whichincreased at early stage, and decreased quickly till fruit maturity, quinic acid and malic acid contents decreased gradually. In both lowbush cultivars’Blomidon’and half-highbush cultivar ’North country’, with quinicacid being the main acid and it presented a decline tendency during the fruit development stage, citric acid and tartaric were the minor components. Sorbitol accounted for 67.28% of total sugar in leaves,and the content reached top at 42 d after full bloom (around 15 d before harvest), then decreased quickly. Sorbitol was the main soluble sugars in leaves.2.In the reciprocal populations of high sugar-high acid blueberry’Sapphire’and middle sugar-low acid blueberry’Berkeley’, fructose and glucose were the major components of sugar, while citric acid and tartaric acid were the major components of acid. The reciprocal populations exhibited wide phenotypic variation in fructose, glucose, total sugar, tartaric acid, citric acid and total acid contents where the coefficient of variation (CV) of sugar and acid contents were more than 15% and 30%, respectively, and the range of acid contents were higher than that of sugar contents, indicated that there was a bigger selected potential for acid content. Mean sugar and acid contents of reciprocal cross progenies were lower than mid-parental values, showing a tendency of depression. The mean sugar contents of progenies inclined to low sugar parent, there exist maternal inheritance on the sugar contents, whilethe mean acid contents inclined to paternal parent value, indicating that the acid contents were mainly affected by paternal parent.. The individual and total sugar contents present a normal distribution, implying sugar contents were quantitative trait and controlled by polygenenes, while individual and total acid present a skewed distribution, implying acid contents were quantitative traits and may be controlled by both major gene and polygenes. The broad sense heritability (H2) of fructose, glucose, total sugar, citric acid and total acid contents were ranged from 0.66 to 0.86, the highest in fructose (0.84 and 0.86 in the reciprocal populations, respectively), indicating that the variations of these traits mainly resulted from inheritance, and they were mainly affected by additive effect, while the H2 of tartaric acidwere lowest (0.22 and 0.30 in the reciprocal populations, respectively), indicating that the variation of tartaric acid was greatly affected by environmentfactors.3. Fructose and glucose were the predominate sugar in both parents and progenies. The broad sense heritability (H2) and genetic transmitting ability (Ta) of total sugar were 0.74 and 0.93, respectively. The segregation of individual and total sugar shown a normal distribution and mean value of progenies were to different degree lower than or similar to mid-parental values, sugar content show additive inheritance. Citric acid was the most abundant acid and the second was the tartaric acid. The H2 and Ta of total acid was 0.73 and 0.90, respectively. Citric acid were the quantitative trait that governed by major gene and additive polygenes. Tartaric acid, however, was mainly controlled by non-additive effect.4. A total of 54 EST-SSR markers were characterized from 120 primer pairs designed by assaying 12 samples of the Vaccinium genus section Cyanococcus. The markers exhibited a high degree of polymorphism and polymorphic information content (PIC) value ranged from 0.430 to 0.912 with an average of 0.772. The cross-species transferability of 54 new EST-SSR markers ranged from 68.5%(V. corymbosum) to 88.9%(V. august ifolium and V.bracteatum). Cluster analysis and Principal Coordinate Analysis (PCoA) based on 54 EST-SSR markers were largely consistent with the traditional taxonomy among the materials tested and indicated that shese primer pairs were effective. Those EST-SSR markers displayed considerable polymorphism and high transferability in both cultivated and wild species of Vaccinium, and will contribute to the studies of genetic diversity, linkage mapping, QTL and molecular assisted breeding of Vacciniumcrops.5.Molecular genetic maps for ’Sapphire’ and ’Berkeley’ were constructed using all separation loci and non deflection loci. The ’Sapphire’ genetic map (including deflection loci)consisted of 12 linkage groups, and covers 12108.72 cM with an average genetic distance of 17.47cM, non deflection loci genetic map covers 2602.54 cM with an average genetic distance of 25.52cM. The ’Berkeley’ genetic map (including deflection loci)consisted of 12 linkage groups, and covers 4039.74 cM with an average genetic distance of 17.34cM, only have 22 non deflection loci. By Chi-square (χ2=0.05). The polymorphic marker segregation ratio of ’Sapphire’ and ’Berkeley’ were 85.28% and 90.56%. respectively.6. Sugars and organic acid content of’Sapphire’.’Berkeley’and their 94 Flprogenies were determined by HPLC, and than scan QTLs for six sugar and acid traits by using inclusive composite interval mapping (ICIM). Through interval mapping,4 QTLs were found when LOD>3 on ’Sapphire’ loci genetic map (including segregation distortion loci), while 3 QTLs were found when LOD>1.5 on ’Sapphire’ non-segregation distortion locigenetic map, the phenotypic variations explained by each QTL more than 10%, all of these QTLs were related with acid content, no sugar QTLs were scanned. There was no related QTLs with sugar and acid content in’Berkeley’. |
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