Hydrangea macrophylla (Thunb.) Ser., an important genetic resource for the development of hydrangea cultivars, is endemic to a limited number of regions in Japan; however, there is a lack of comprehensive phytogeographical information essential for the conservation and effective utilization of this valuable genetic resource. In this study, we investigated the occurrence of natural hybridization between H. macrophylla and H. serrata within the distribution range of H. macrophylla by analyzing the internal transcribed spacer (ITS) regions of nuclear ribosomal DNA. Analysis of the H. macrophylla genome database revealed approximately 300 tandem repeats of ITS sequences in the genome. Two major ITS sequences, accounting for 55% to 59% of the total ITS sequences in the genome of H. macrophylla Aogashima-1 (the individual used for genome assembly), appeared to be inferable from electropherogram data obtained by direct sequencing of PCR products. From a total of 320 samples of H. macrophylla and H. serrata, 10 ITS types were identified. As a result of phylogenetic analysis, the ITS sequence types of H. macrophylla, H. serrata var. yesoensis, var. serrata, var. angustata, and some var. acuminata samples were grouped into a single cluster. Samples were collected from four of the Izu Islands, 16 populations on the Izu Peninsula, and 12 populations on the Boso Peninsula to estimate the occurrence of interspecific hybridization within the H. macrophylla distribution range. Direct sequencing results for PCR products of ITS sequences and morphological data showed that little interspecific hybridization had occurred in the Izu Islands; however, hybridization had occurred in many populations on the Boso and Izu Peninsulas. Furthermore, our findings suggest that habitat topography influences the frequency of interspecific hybridization among H. macrophylla populations. To conserve H. macrophylla genetic resources in the Boso and Izu Peninsulas, it is important to consider not only population decline, but also the impact of natural interspecific hybridization.

Drought and global warming affect the photosynthesis and various physiological processes of plants in Asian forest ecosystems. Improving physiological responses is the best way to overcome challenges to survival under drought and higher temperatures. This study was conducted to appraise the role of silicon (Si) in enhancing the drought tolerance and chlorophyll fluorescence response in banyan trees (Ficus annulata) in a pot experiment for 18 days. Three treatments were tested: control (CF), drought (DT), and drought stress sprayed with Si (DS). At the end of the trial, Si foliar spray at a concentration of 15 mM significantly increased (P < 0.05) the leaf relative water content (RWC) by 90%, total chlorophyll by 3.3 mg·g−1 FW, photosynthetic rate by 6.7 μmol CO2·m−2·s−1, stomatal conductance by 0.26 mol H2O·m−2·s−1, and transpiration rate by 2.7 μmol H2O·m−2·s−1. Moreover, ABS/RC, DIo/RC, TRo/RC, and ETo/RC were significantly lower than those under drought stress, while Fv/Fm and Pi were substantially higher than those under drought stress (P < 0.05). The levels of hydrogen peroxide (H2O2) production, electrolyte leakage (EL), and malondialdehyde (MDA) were considerably reduced during the drought stress experiment with Si spraying (P < 0.05). Foliar Si spraying did not enhance TSS content, but positively affected proline content (P > 0.05). The findings suggest that Si supplementation effectively improved the physiological responses, photosynthetic pigment content, and photochemical efficiency of F. annulata under drought conditions.

Double fertilization is essential for sexual reproduction in flowering plants. However, with ongoing global climate change, the increasing frequency of abiotic stresses such as extreme heat and cold has posed significant challenges to plant reproductive development. Temperature fluctuations significantly impact key stages of male gametophyte development, including pollen germination, pollen tube growth, and generative cell division. Disruptions to these processes can lead to reduced fertilization efficiency, thereby impairing fertility and crop yield. Although polyploid plants generally exhibit enhanced tolerance to abiotic stress, the mechanisms by which pollen from polyploid plants regulate reproductive cell division under temperature stress remain poorly understood. In this study, we investigated the dynamics of pollen tube development and generative cell division in diploid and tetraploid Lilium leichtlinii ‘Hakugin’ under various temperature treatments including 12°C, 17°C, 22°C, 27°C, 32°C, and 37°C. Flow cytometry was employed to monitor changes in nuclear DNA content during pollen tube elongation, allowing assessment of generative cell division. The results revealed that high-temperature exposure at 37°C markedly suppressed the generative cell division process in diploids, suggesting possible heat-induced cell cycle arrest. In contrast, after 24 h of incubation at 37°C, the completion rate of generative cell division in pollen tubes from tetraploid plants was consistently higher than that in their diploid counterparts. These findings demonstrate that polyploid plants have advantages in cell cycle regulation under heat stress. This trait may help them better cope with heat conditions during reproductive development. Our results provide new insights into the robust reproductive development of polyploid plants under heat stress.

Vegetable plug seedlings have a short optimal transplanting period. Fertilizer restriction can extend this period, but the effect on later growth remains unclear. We investigated the effects of long-term storage of broccoli plug seedlings (Brassica oleracea L. var. italica) with fertilizer restriction on leaf number increase, leaf expansion, and the timing of flower bud differentiation in spring and autumn crops. In addition to conventional one-month seedlings (1 MS), we prepared 2- and 4-month seedlings (2 MS, 4 MS) and planted them all out on the same day. Seedling storage had no effect on the rate of leaf number increase or the timing of flower bud differentiation. These results suggest that the transition from vegetative to reproductive growth is not affected by seedling storage, and is instead determined by the leaf number increase after transplanting (regardless of storage period, the plants developed about 13 leaves after transplanting in autumn). However, longer storage suppressed the expansion of leaves that had appeared before transplanting, particularly during the first 20 days after transplanting, resulting in a lower relative expansion rate. This difference was more pronounced in the autumn crop, and was thought to be due to differences in temperature during the early stages after transplanting between spring and autumn crops. We found no significant relationship between seedling storage and head diameter or weight at harvest, but we found a positive correlation between leaf area during the growth period after transplanting (except for a certain period immediately after transplanting) and head weight, particularly during the flower bud differentiation stage. Therefore, seedlings stored for longer tend to exhibit suppressed leaf expansion. As a result, differences in leaf area after transplanting may mediate the effect of seedling storage on head weight.

Fruit cracking is a fruit peel physiological disorder. In citrus, it typically results in fruit splitting and abscission. Cracking is related to plant water factors and the irrigation regime; heavy or non-regular irrigation is correlated with elevated cracking incidence. In addition, cracking is more common in larger fruit than in smaller ones. Some cultivars are more prone to cracking, suggesting that the phenomenon has a genetic background. However, it has become evident that climatic conditions also affect fruit cracking. As a result, some years are characterized by heavy cracking incidence, and this may be associated with yearly climate variations. Top netting is a useful tool to mitigate microclimates, and it can potentially reduce cracking intensity. We conducted a five-year experiment in a commercial ‘Valencia’ orange orchard, using three different photoselective nets and three distinct irrigation regimes: the recommended level (100%), and two reduced regimes (80% and 60%). Out of the five experimental years, cracking occurred in three years with various intensities. As expected, reduced irrigation in control trees resulted in decreased cracking intensity, and there was a positive relationship between the fraction of cracking and larger fruit size. In netted trees, the cracking intensity was reduced regardless of net color, irrigation regime or fruit size. During the summer, canopy temperature was reduced under the nets, and relative humidity increased. The possible involvement of climatic parameters, modified under the nets, in altering cracking intensity is discussed. Results of this experiment demonstrate the potential of top-netting technology to mitigate cracking intensity in citrus.

Kiwifruit flowers have approximately 40 stigmas. Artificial pollination is essential for dioecious kiwifruit production. We investigated the effect of the pollination site on seed distribution, fruit size and quality. We found that seeds should be evenly distributed in the fruit to improve fruit shape and that seed number and total soluble solids (TSS) were not positively correlated. We also noted that seeds were distributed in a spreading manner away from pollinated stigma. This indicated that the stigma and carpel had a similar one-to-one like connection. However, the connection was not exact, and seeds were distributed not only in a particular carpel, but also slightly the outside the carpel. Seeds were distributed uniformly in the fruit even when pollination was limited to the two most distant stigmas, and the number of seeds increased when the number of pollinated stigmas increased. These results indicated that it was not necessary to pollinate all stigmas, but only several stigmas, in order to achieve larger fruit size.

Fruit consumption is highly recommended due to its health benefits. Passiflora species are a good source of vitamins and antioxidant compounds such as carotenoids that are associated with a reduction in cellular oxidative processes, as well as against cardiovascular diseases and cancer development. As a result, purple passion fruit (P. edulis) and yellow passion fruit (P. edulis f. flavicarpa) are economically important crops that are cultivated based on the demand for their flavor and nutraceutical properties. The objective of this study was to determine the components of carotenoids and sugars in the pulp juice of passion fruit. Two Ecuadorian yellow passion fruit strains (‘INIAP 2009’ and ‘POR1’), one Ecuadorian purple passion fruit variety (‘Gulupa’) and two Asian hybrid cultivars (P. edulis × P. edulis f. flavicarpa; ‘Summer Queen’ and ‘Ruby Star’) were used for this research. The results showed that ‘POR1’ had high acidity and contained all carotenoids, but had the lowest amount of vitamin C, whereas ‘INIAP 2009’ had high contents of organic acids, vitamin C and β-cryptoxanthin. ‘Gulupa’ had the lowest acidity, α-carotene and citric acid content, but the highest amount of glucose, fructose, malic acid and vitamin C; this variety also showed high values of β-carotene and β-cryptoxanthin. On the other hand, ‘Summer Queen’ had high sucrose, malic acid, α and β-carotene and good amount of vitamin C, while ‘Ruby Star’ had high amounts of α-carotene, β-cryptoxanthin and citric acid, but low vitamin C content. These results can be used for further breeding programs focused on improving passion fruit quality.

Paprika (Capsicum annuum L.) is known for its abundant functional components such as carotenoids and phenolics. Growth responses to nutrient conditions including nitrogen (N) have been studied. However, there has been only limited analysis on the variations in components in response to N. This study investigated the effects of different N levels on the functional components of paprika. Paprika was grown under different N conditions and ripe fruits were harvested. Subsequently, mineral, carotenoid, phenolics, and sugar contents were measured. Higher N supply increased fruit weight and carotenoids, but reduced phenolics and glucose. The negative correlation between carotenoids and phenolics suggests complementary antioxidant functions in fruits, while the significant association between these metabolites and boron and potassium implies that these elements may have indirectly influenced metabolic pathways. Moreover, specific components like phenolics indicate a trade-off with yield. Capsanthin alone was significantly affected by N supply, suggesting downstream effects on the carotenoid biosynthetic pathway. This study will contribute to the optimization of N fertilizer application for balanced paprika production with high quality and economic yield.