Abstract
‘Minihyang’ mandarin bears fruits with small size and high sugar content. ‘Minihyang’ mandarin grafted on trifoliate orange (TO) tends to be vigorous and develops water sprout open. It is associated with insufficient floral differentiation and fruit set. Recently, the use of Flying Dragon (FD) as rootstock with a high dwarf effect has been proposed to improve this situation. Therefore, this study was conducted to evaluate the effect of two different rootstock genotypes on tree growth, fruit yield, and fruit quality at the physiological, biochemical, and molecular levels. As a result of the study, in FD, tree vigor was stably maintained, fruit size was large, and the sugar content was high compared to the TO. Fructose, glucose, and sucrose of fruit continued to increase from development to maturity. In particular, fructose and sucrose were significantly higher in the fruits of the FD than those in TO at 150 and 220 days after anthesis. The total sugar content was also significantly higher in the fruit of the FD. The activities of SPS and SS associated with sucrose synthesis tended to be increased during the fruit maturity season, but there was no significant difference between the two rootstocks. On the other hand, the activities of SS and AI breaking down sucrose were high in FD at 150 and 220 days after anthesis. These results suggest that the unloading of sucrose might be increased and affect the sugar content. However, the results of real-time PCR analysis of gene expression related to sucrose metabolism did not show an association with changes in enzyme activity affecting sugar content. Therefore, further detailed studies on the process after the regulation of gene expression are likely to be needed.
Highlights
The citrus is one of the most important fruit crops in Korea and the world
The difference of sugar content and composition in citrus was associated with the rootstock genotypes [7,8], which might be attributed to the degree of sucrose metabolismrelated enzyme activities and gene expression
Mandarin grafted on Flying Dragon (FD) was 1.4 m, whereas that grafted on the trifoliate orange (TO) was 4.0 m, which had a difference of about three times
Summary
Citrus fruits contain various nutrients, such as vitamin C, minerals, flavonoids, and fiber, playing a crucial role in improving health and preventing chronic diseases [1]. It accounts for about 32% of the total fruit production, which ranks first among the fruits in Korea [2]. The difference of sugar content and composition in citrus was associated with the rootstock genotypes [7,8], which might be attributed to the degree of sucrose metabolismrelated enzyme activities and gene expression. This study was conducted to evaluate the effect of the rootstock on the sugar content of ‘Minihyang’ citrus fruits and scion tree growth and yield and to analyze the relationship between the sucrose metabolism enzyme activity and gene expression patterns
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