A study of genetic trend of sugar and acid components in the fruits of apple hybrid progeny of ‘Jonathan’ × ‘Golden Delicious’

Abstract: 【Objective】Sugars and acids are the main components determing fruit eating quality in apple.Sugar and acid composition is also related to the flavor of the fruits. Previous study showed that the totalsugar content of apple fruit was controlled by multiple genes and total acid content was controlled by ma⁃jor gene although the cases were not always the same. There were a few reports on genetic trend of sugarand acid components. Therefore, it is necessary to carry out further research on the inheritance of sugarand acid components for providing more reference for quality breeding in apple.【Methods】The parentsand hybrid progeny of‘Jonathan’בGolden Delicious’were used as materials. The sugar and acid components of the fruits of the parents and the 186 hybrid seedling trees were measured by using high performance liquid chromatography (HPLC). The flesh of matured fruit was cut into small pieces and put in liq⁃uid nitrogen. Then they were ground by SPEX6870 frozen mill into pulp and were stored at -20 ℃. Onegram pulp was put into the 10 mL centrifuge tube, adding 4 mL redistilled water for mixing, and it waskept static at room temperature for 10 min for sugar components extraction. The samples were centrifugedat 10 000 g for 15 min at 4 ℃. The supernatant was filtered through a 0.45 mm filter to 1.5 mL tube, andwere stored at -20 ℃ for test. Sugar components were measured by LC-10ATVP HPLC. The column wasCLC-NH2, column temperature was 40 ℃. The mobile phase was 80% acetonitrile. The flow rate was 0.7mL·min- 1. The samples were injected by automatic sampling device. The injection volume was 10 μL.The samples were detected with RID-10A refractive index detector. For acids extraction, two grams ofpulp were put in 10 mL volumetric flask, and extracting solution (0.2% metaphosphoric acid) was added toconstant volume. After ultrasonic extraction for 15 min, the solution was transferred to 10 mL centrifugetube, and was centrifuged at 10 000 r·min^-1 for 15 min at 4 ℃, the supernatants were decanted and filtered through a 0.45 mm filter to 1.5 mL tube, and were stored at -20 ℃ for test. Acid components weremeasured by Dionex U3000 HPLC, with VWD UV detector. Chromatography column was Welch materialsC18 column (250 mm×4.6 mm). The mobile phase was 0.2% metaphosphoric acid. The flow rate was 1mL·min-1, column temperature was 35 ℃. The injection volume was 20 μL. The histogram and normal distribution of sugar and acid components were mapped with Excel. All statistical analyses were performedby Excel.【Results】The sugar components of the fruits of the hybrid progeny were quantitative characters according to the normal distribution. Fructose, glucose and sucrose were main sugar components in the fruits of parents and their F1 offsprings. The ratio of fructose and glucose was lower in the parents than that in the offspring. The average content of fructose, glucose and sucrose in the fruits of hybrids were 39.86, 15.46 and 23.02 mg·g^-1. The genetic transmitting ability（Ta）were 71.59%，65.56% and 182.55% respectively. Fructose and glucose were mainly controled by additive effect although they were partially controled by non-additive effect. Malic acid, sitric acid, succinic acid and oxalic acid were main acid components in the fruits of parents and their F1 offsprings. The content of malic acid in F1 generation displayed a continuous distribution and was probably governed by polygenes. The content of oxalic acid, succinic acid and citric acid displayed a noncontinuous distribution. The ratio of individuals with lower content (<0.04 mg·g^-1) and higher content (>0.04 mg·g^-1) of oxalic acid in the progeny was 177∶9, close to 15∶1. The ratio of individuals lower content (<0.03 mg·g^-1) and higher content (>0.03 mg·g^-1) of succinic acid content in the progeny was 106∶80, close to 9∶7. The ratio of individuals lower with lower content (<0.03 mg·g^-1) and higher content (>0.03 mg·g^-1) of citric acid in the progeny was 105∶81, close to 9∶7. The average contents of malic acid, citric acid, succinic acid, oxalic acid in the fruits of hybrid progeny were 0.55, 0.04, 0.03 and 0.02 mg·g^-1and the values of Ta were 90.09%, 57.62%, 84.26% and 91.57% respectively. 【Conclusion】Fructose, glucose, sucrose and malic acid were quantitative characters governed by polygenes. The content of oxalic acid, succinic acid and citric acid were mainly governed by two major genes and partially by polygenes. The two major genes had complementary effect on controlling succinic acid and citric acid content respectively.