To explore the physiological and biochemical differences between different ploidy Luculia pinceana Hook. varieties and to obtain germplasm resources with excellent horticultural characteristics and strong resistance, we analysed and compared the morphological characteristics, photosynthetic properties, and physiological indices of diploid and tetraploid L. pinceana. (1) Tetraploid L. pinceana exhibited distinct polyploid characteristics, including a smaller plant, rounder, thicker, and darker green leaves, as well as coarser and longer leaf and stem hairs. Moreover, the flowers of tetraploids are relatively large, and the diameters of the flowers, the lengths of the corolla tubes and the lengths of the pistils are all extremely significantly greater than those of diploids. Compared with those of tetraploids, the leaf width and thickness of the diploid plants increased by 16.38% and 14.71%, respectively, whereas the leaf length, leaf area, and plant height decreased by 21.20%, 3.46%, and 54.86%, respectively. (2) The diurnal variation curve of photosynthesis in L. pinceana was unimodal, reaching a maximum value at approximately 10:00. Compared with diploid plants, tetraploid plants presented a significantly greater maximum net photosynthetic rate (Pmax), light saturation point (LSP), and light compensation point (LCP). (3) Compared with diploids, tetraploid leaves presented significantly greater activities of antioxidant enzymes, including superoxide dismutase (SOD, + 51.61%), peroxidase (POD, + 6226%), and catalase (CAT, + 211.66%). Additionally, the concentrations of osmolytes [soluble sugar (SS, + 80.11%), soluble protein (SP, + 63.49%), and proline (Pro, + 57.40%)] were markedly elevated. Conversely, the malondialdehyde (MDA) content was substantially decreased (-46.16%). These results demonstrate that the tetraploid L. pinceana has greater ornamental value, fertility and resistance. It is an excellent breeding material for the germplasm resources of L. pinceana and provides a material basis for the cultivation of new varieties of L. pinceana.

Fragrant rhododendron varieties remain relatively limited in current germplasm resources, constraining the enhancement of ornamental and aromatic characteristics in rhododendron breeding—this limitation has emerged as a critical bottleneck in the genetic improvement of rhododendrons. This research takes fragrant flower breeding as the breeding objective and conducts hybridization between varieties of the subgenus Tsutsusi, which can flower in multiple seasons and exhibit relatively strong resistance, and the fragrant R. moulmainense. Parallel intraspecific hybridizations within the subgenus Tsutsusi were implemented as experimental controls to quantify hybridization affinity. This study combines floral tube ontogeny histomorphological analysis, ovary paraffin sectioning, and optimized pollination protocols to address hybridization constraints, providing new insights for rhododendron intersubgeneric distant hybridization to create fragrant varieties. The results showed varying fertility among combinations, with some showing sterility or weak fertility due to low pollen germination and abnormal embryo development. Both pre- and post-fertilization reproductive barriers were observed, and different pollination methods significantly influenced ovary expansion and fruit set rates. Regarding limitations, this study lacks an in-depth analysis of reproductive isolation mechanisms, only describing phenotypic characteristics through morphological and histological methods, and it does not employ molecular techniques. The fundamental causes of reproductive isolation between subgenera therefore remain unclear. Additionally, there was no long-term monitoring of seedling emergence rates, hybrid plant growth potential, or flowering traits. This limits the ability to comprehensively evaluate the breeding value and genetic stability of distant hybrids.

Background: Drought conditions limit the distribution of Bougainvillea varieties, reduce their ornamental value, and increase maintenance costs. Although the rhizospheric melatonin-mediated mechanisms of plant drought resistance have been extensively documented. its role in the drought stress response of Bougainvillea , especially the regulatory effect on rhizosphere microorganisms, remains unclear. Using Bougainvillea glabra ‘Cypheri’ as plant material, this study employed a pot-based natural drought experiment combined with physiological indicator measurement, rhizosphere microbiome high-throughput sequencing, microbial network analysis, PICRUSt2 functional prediction, and redundancy analysis (RDA) to systematically investigate the regulatory mechanisms of melatonin on aboveground-belowground synergistic drought resistance. Results: Compared with the control group, drought stress significantly enhanced the activities of superoxide dismutase (SOD), peroxidase (POD), and catalase (CAT), as well as the proline (Pro) content in Bougainvillea , while increasing malondialdehyde (MDA) accumulation. Conversely, leaf relative water content (RWC) and chlorophyll (Chl) content were markedly reduced. Simultaneously, the rhizosphere microbial community balance was disrupted, bacterial network robustness diminished, and carbon metabolic pathways were suppressed. Exogenous melatonin application further significantly enhanced antioxidant enzyme activities and Pro accumulation under drought stress, reduced MDA content, and improved the physiological status of plants. Simultaneously, it promoted the enrichment of Proteobacteria, modulated the abundance balance of Ascomycota, enhanced microbial network stability, and optimized carbon, nitrogen, and energy metabolic pathways. Collectively, these results demonstrate that melatonin enhances drought tolerance in Bougainvillea by regulating the structure and network stability of rhizosphere microbial communities, synergistically improving aboveground drought resistance physiology, and mediating aboveground–belowground synergistic interactions. Conclusion: This study provides a theoretical foundation for the application of melatonin in drought-resistant cultivation practices for Bougainvillea species.