QTL mapping of fruit sugar and acid traits in the F₁ generation of jujube (Ziziphus jujuba Mill.)

Jujube (Ziziphus jujuba Mill.) is one of China’s important specialty fruit trees with high nutritional and medicinal values. With the growing demand for high-quality jujube fruit, genetic improvement of fruit quality has become a key focus of the jujube industry. Fruit flavor is critical for market competitiveness, and soluble solids, soluble sugar and titratable acid are the main components determining fruit flavor quality.

To analyze the genetic inheritance of sugar and acid traits in jujube fruits, the F1 generation of 140 progeny from the cross between jujube ‘Yuhong’× ‘Jiaocheng 5’ was established and used for the measurement of sugar and acid contents for a period of 3 years. Thereafter, based on a well-constructed, high-density genetic map of jujube, quantitative trait locus (QTL) localization analysis was carried out. The results showed that a total of 11 QTLs were detected across the sugar and acid traits, which distributed across 6 chromosomes, with LOD values between 3.01 and 4.64, and phenotypic variance explained (PVE) ranged from 12.84% to 23.34%. When the LOD was ≥ 3.5 and PVE ≥ 10%, a total of 5 major QTLs were detected. In the LG1 chromosome, there was one overlapping interval for the traits of soluble solid content and soluble sugars between 35.33 cM and 43.02 cM. In the region from 162.86 cM to 217.25 cM, one overlapping interval for the titratable acidity trait was detected in both 2021 and 2023, with PVE values all above 15%. In addition, within the stable QTL intervals, the candidate genes related to the accumulation of sugar and acid were first screened. Quantitative real-time PCR (qRT-PCR) was employed to analyze the expression patterns of these candidates, leading to the identification of two genes (LOC107416407, LOC107409930) potentially associated with sugar content trait. Bioinformatics analysis revealed that LOC107416407 contains a conserved PFK domain, suggesting it encodes phosphofructokinase, a key regulatory enzyme in glycolysis. LOC107409930 harbors a TPT domain and belongs to the triose-phosphate transporter family. These findings provide a crucial theoretical basis for further investigating the functions of these two genes in sugar accumulation of jujube fruit.

In summary, eleven QTLs and two stable overlapping intervals were detected on the LG1 chromosome. The sugar-related QTL interval is unreported previously and may contain novel genes for sugar accumulation. 2 candidate genes were identified, whose functions are related to sugar metabolism. This study provides theoretical basis, molecular markers and gene resources for exploring sugar metabolism mechanisms and quality-oriented breeding of jujube.