Calcium (Ca) in flesh fruits is important for quality formation and maintenance. Most studies on fruit Ca focus on one species. This study attempted to understand some universal relations to fruit Ca uptake across species. Calcium contents in fruit tissues were analyzed in different fruits, including three cultivars of litchi, two cultivars each of grape and citrus, and one cultivar each of loquat, apple, pear, Indian jujube, and longan. In situ Ca distribution was revealed with electron probe and xylem functionality visualized by dye tracing. Fruit Ca uptake rate and activity were calculated and correlated with fruit growth and pedicel anatomy. The results showed that fruit Ca uptake rate was the highest in pomes (loquat, apple, and pear), followed by Indian jujube drupe, arillate fruits (litchis and longan) and citrus, while grape berries were the lowest. Fruit Ca uptake rate showed a strong positive correlation to growth rate. However, Ca uptake activity, reflecting Ca uptake rate relative to growth, was the highest in arillate fruits and loquat and lowest in grape berries, and had a poor correlation with fruit growth rate. In all fruits, Ca concentration in the pedicel was higher than in the fruit, and they displayed a good positive correlation. In the pedicel, Ca was most abundant in the phloem. Dye tracing showed that xylem function loss occurred with maturation in all species/varieties. Apple had the poorest xylem functionality with the least development of secondary xylem, but its Ca uptake rate was among the highest. Vessel density, size and area in the pedicel showed no correlation with fruit Ca uptake rate. It is concluded that: (1) fruit growth may be a key determinant of Ca uptake; (2) the universal pattern of Ca being higher in the pedicel than in the fruit indicates existence of a pedicel-fruit “bottleneck” effect in Ca transport across species; (3) xylem functionality loss with fruit maturation is also a universal event; (4) in the pedicel, Ca is more distributed in the phloem; (5) vessel morphology in the pedicel is not rate-limiting for fruit Ca uptake; (6) phloem pathway might contribute to fruit Ca uptake.

Calcium (Ca) deficiency in fruit causes various physiological disorders leading to quality loss. However, disorders related to Ca deficiency are not simply caused by a shortage of calcium supply. Ca distribution is also an important relation. This study examined Ca distribution pattern in fruit and pedicel in litchi (Litchi chinensis Sonn.) and the influence of Ca channel inhibitor La3+ on fruit Ca uptake and distribution. In situ distribution of Ca in the phloem and xylem tissues of the pedicel was visualized by Ca mapping with X-ray microanalyzer. Ca2+ analogy Sr2+ was used to trace Ca2+ transport pathway to fruit as well as distribution pattern. The results showed Ca was more distributed in the pericarp, especially the distal part. Ca level in the bark/phloem was always significantly higher than in the xylem and increased with stem age, suggesting constant influx of Ca into the phloem from the xylem. La3+ increased the ratio of Ca in the xylem to that in the bark in the pedicel and significantly reduced Ca accumulation by 55.6% in fruit, suggesting influx of Ca into the symplast was involved in fruit Ca uptake. Sr2+ introduced from fruit stalk was found to be transported to fruit through the phloem as Sr was largely distributed in the phloem, and fruit stalk girdling significantly reduced Sr accumulation in the pericarp. Ca mapping across the pedicel revealed Ca-rich sites in the parenchyma cells in the phloem and along the cambium, where abundant Ca oxalate crystals were found. The results suggested extensive influx of Ca from xylem/apoplast pathway into the phloem/symplast pathway in the pedicel, which enables phloem/symplast pathway to contribute a considerable part to Ca uptake in litchi fruit.

Since ancient times, grafting has been utilized to develop horticultural crops to increase plant vigor, yield potential, and tolerance to various environmental stresses. Grafting employs selected rootstocks of the same species or near relatives. Moreover, dwarfing is desirable for intensive cultivation and efficient orchard management. However, information on the regulatory mechanisms regulating rootstock-induced vigor remains unclear. Numerous studies comprehend the physiological and molecular mechanism of rootstock control scion vigor, which has significantly improved our understanding regarding vigor control processes in apple, litchi, pear, citrus, etc. This review summarizes the current knowledge on the impact of rootstocks on scion vigor and hormonal mechanisms involved in dwarfing, such as auxin (IAA), cytokinins (CK), abscisic acid (ABA), gibberellic acids (GAs), and brassinosteroids (BR). This study will provide fascinating information for future studies on rootstock-induced dwarfing effects and accelerate the breeding of dwarfing rootstocks.

Dwarfing rootstocks are a valuable genetic resource for managing high-density plantations. The selection of the appropriate scion/rootstock combination is key to improving crop performance and sustainable production in a particular environment and specific training systems. ‘Shatangju’ mandarin scion cultivar grafted onto ‘Flying Dragon’ rootstock tends to be dwarfing and develops short stature plants. To obtain insight into potential mechanisms underlying rootstock-induced dwarfing effects, we conducted a rootstock trial to examine the influence of 11 different rootstocks based on their growth vigor, antioxidants, and hormonal levels of the scion cultivar. The phenotypic observations revealed that size reduction in the ‘Flying Dragon’ rootstock is due to lower node number, shorter internodal length, and a reduced trunk diameter of the scion compared with more vigorous rootstocks. Antioxidant analysis showed that ‘Shatangju’ mandarin grafted onto ’Flying Dragon’ and ‘Trifoliate Orange’ rootstock had significantly lower peroxidase (POD) activity than other tested rootstocks. The hormonal analysis indicated that there were markedly lower amounts of abscisic acid (ABA) in ‘Shatangju’ mandarin grafted with ‘Flying Dragon’ rootstock. In addition, trees grafted with ‘Sour Pummelo’ and ‘Flying Dragon’ depicted minimum amounts of gibberellins (GA24). Moreover, several metabolites associated with organic acids, flavonoids, amino acids, and alkaloids responded differently in plants grafted with ‘Flying Dragon’ (dwarfing) and ‘Shatang Mandarin’ (vigorous) rootstocks. This study concluded that ‘Flying Dragon’ rootstock with a strong dwarfing effect has been proposed to improve high-density cultivation methods. These findings will provide useful insights for future research associated with rootstock-mediated dwarfing mechanisms of citrus rootstocks.

Kalimantan Island is rich in genetic resources and species diversity of Durio spp. plant. The large number of Durio species that grow in Kalimantan illustrates that this area is the most important distribution center for durian relatives. The best-known edible durians are Durian (Durio zibethinus). However, Kalimantan also has various types of Durian that are not yet widely known and have superior potential. One of the unique and exotic plants is the red flesh Durian in East Kalimantan, Indonesia. The fruit of this plant is unique because it has red flesh. At present, there is no morphological identification of this East Kalimantan Durio graveolens plant. The study aimed to identify the morphological character of Batuah D. graveolens from East Kalimantan, Indonesia. This research was carried out by collecting data and information about the morphological characteristics of the plant and fruits. The results of the study successfully identified Batuah D. graveolens from East Kalimantan as a plant diverts from another Durio spp. plant known like D. zibethinus and D. kutejensis especially for red flesh character.