The type and content of organic acids in fruits are important factors that determine the traits, such as the nutrition and flavor of fruits. Fruit weight and size are also very important economic characters in fruit breeding research. To investigate the inheritance patterns in longan, fruit organic acid contents, weight, and size were measured in the distant hybridization progenies of longan ‘Huanongzao’ and lychee ‘Ziniangxi’. The results revealed that the malic acid accumulation exhibited mid-parent heterosis, citric acid content showed a tendency towards depression, and oxalic acid, ketoglutaric acid, fumaric acid, gallic acid, and total acid contents exhibited transgressive inheritance. The inheritance patterns in fruit weight, length and diameter tended towards smaller and degraded. The coefficient of variation (CV) for the organic acids ranged from 35.77–90.20%, and the heritability (H²) was 72.35–97.44%. High CV (55.44%) coupled with medium H² (28.72%) were observed in fruit weight, however, low CV (12.29% and 12.50%) coupled with high H² (68.95% and 69.25%) were shown in fruit length and diameter. In this study, the genetic variation of acid contents, fruit weight and size in the F₁ population of longan and lychee were analyzed for the first time, providing an informative and theoretical basis for the selection and breeding of longan cultivars.

Dragon fruits have abundant nutritional and antioxidant properties. High temperatures limit the growth and production of dragon fruits. Hemin can effectively alleviate abiotic stress in plants. However, the regulatory effect of Hemin on dragon fruit under heat stress remains unclear. In this study, we explored the impacts of foliar application of Hemin on dragon fruit size, yield and quality during the high temperatures of the summer season. In this experiment, dragon fruit variety ‘Jindu No. 1’ was used as material and treated with three Hemin concentrations, i.e., H1: 1 μmol.L⁻¹, H2: 10 μmol.L⁻¹, H3: 100 μmol.L⁻¹, compared with CK: control. The results show that exogenous Hemin increased the single fruit weight, yield, fruit shape index and edible rate. It also improved pericarp L* value, a* value, C* and decreased h^o, improving the peel colour; exogenous Hemin enhanced soluble solids content and phenolic compounds content and antioxidant enzyme activities in the pulp of dragon fruit. In addition, exogenous Hemin increased the content of chlorophyll content in dragon fruit stems. Differential metabolites determined by metabolomic assay also indicated that Hemin significantly increased the content of active substances such as selagin. Additionally, the Hemin treatment H2 also activated the activity of antioxidant enzymes such as superoxide dismutase (SOD), peroxidase (POD), catalase (CAT), and ascorbate peroxidase (APX), which helps to mitigate the effects of high temperatures on dragon fruit. The current findings strongly advocate that H2 treatment may effectively counteract the adverse effects of heat stress by regulating the morph-physiological and antioxidant traits.