Analysis of genetic variation of sugar and acid contents in F1 population of apricot derived from ‘Chuanzhihong'בLuotuohuang'

Abstract: 【Objective】The objective of present study is to analyze the genetic variation of sugar and acid contents in apricot F1 population in order to provide a basis for selecting parents in cross breeding of apricot.【Methods】Crossing was carried out between‘Chuanzhihong'and‘Luotuohuang'in Beijing.The contents of sucrose, glucose and fructose of the fruits of two parents and their progenies were investigated with ion chromatography, and malic acid and citric acid were determined by high performance liquid chromatography (HPLC) method. About 1 kg fruits with the same maturity for each hybrid individual were randomly taken from the middle of the peripheral crown in four directions on 9 :00—11:00, and then put into a 4 ℃ box and brought back to the laboratory. The fruits were kept at 4 ℃ in a fridge and evaluated within 1 day. The samples for each hybrid were divided into 3 portions as three replicates. The middle of pulp was homogenized and divided into 2 parts and stored in the refrigerator at -70 ℃. One part was used to determine the contents of sugars, and the other to determine the contents of acids. Five trees of each parent were selected to determine the content of sugar and acid components, and the sampling method was the same as above. The contents of sugar and acid componentswere used to calculate the variance of the parents. The solutions of the apricot hybrids containing released sugars were detected by Dionex ICS-3000 Ion chromatograph. Sucrose, glucose and fructose were separated on Carbo Pac PA1 4 mm×250 mm (with a Carbo Pac PA1 4 mm×50 mm guard column) at 30 ℃ with injection volume of 10 μL using 200 mmol·L^-1 sodium eluting hydroxide as leaching liquid at the rate of 1 mL·min-1 detected by pulsed amperometric detector (Au electrode) . The organic acids of apricot hybrids were analyzed by Dionex P680 High-performance liquid chromatography. Malate and citrate were detected with a DIONEX PAD-100 detector. The Agilent poroshell 120 SB-C18 column (250 mm × 4.6 mm i.d., 2.7 μm particle size) with a guard column cartridge (Sunchrom C18 cartridge) was used to maintain at 30 ℃. Samples were eluted with 0.02 mol∙L-1 M solution (M indicated A∶B=99.5∶0.5, A indicated that 2.28 g K2HPO4· 3H2O dissolved in 1 L of water, adjusted with H3PO4 to pH=2.7; B indicates methanol) at the rate of 1 mL · min-1 at pH=2.4 and detected by UV absorbance at 210 nm.【Results】The sucrose was the main sugar in soluble sugars of the fruits of apricot hybrids, whose variation range was 67.60-109.10 mg∙g-1 and 19.50-92.60 mg∙g-1 in 2015 and 2016, respectively. Sugar and acid components (except for the citric acid) , total sugar and total acid showed a normal distribution, indicating that they were quantitative traits controlled by multiple genes, while citric acid presented a skewed distribution, implying that acid contents were qualitative traits and might be controlled by both major gene and polygenes. The extreme values of different sugars, acid components and total sugar and total acid indicated that there were some promising individuals in the progenies which could be potentially used as parent for breeding high sugar or high acid apricot varieties. The populations exhibited a wide phenotypic variation in fructose, glucose, total sugar, tartaric acid, and total acid contents where the coefficient of variation (CV) of sugar and acid contents were over 20%, and the range of acid contents was higher than that of sugar contents, indicating that there was a larger selecting potential for acid content. The content of sucrose, citric acid and total acid of the hybrids were lower than the medium value, representing a decline variation. The broad sense heritability (H2) of fructose, glucose, total sugar, citric acid and total acid contents were over 0.70, in which the H2 of sucrose was higher than that of glucose, fructose and total sugar and citric acid was higher than that of malic acid, indicating that variations of these traits mainly resulted in inheritance.【Conclusion】Sucrose, glucose, fructose and malic acid were the quantitative traits controlled by the multiple genes, while citric acid might be qualitative traits and might be controlled by both major gene and polygenes in the F1 population of‘Chuanzhihong'and‘Luotuohuang'.