Dahlia (Dahlia variabilis) flower colors are diverse and are determined by the accumulation of flavonoids. Cultivars with dark red flowers accumulate more anthocyanins in their petals. Flower color changes such as color fading often occur in some cultivars. In this study, low minimum temperature regulated flower color fading and flavonoid synthesis in dahlia ‘Nessho’ were investigated. The pigment contents and expression levels of flavonoid biosynthesis genes were investigated in detail under several growing environments in which color fading occurs. Flavones accumulate more in color-faded orange flowers than in dark red ray florets. The expression analysis of the anthocyanin synthesis pathway genes indicated that the upregulation of flavone synthase (DvFNS) gene expression correlated with the high accumulation of flavones in color-faded petals. DvFNS expression was also detected in young leaves, and the expression level was higher in winter than in summer. Seasonal changes in DvFNS expression in young leaves significantly correlated with color fading in petals. The change in DvFNS expression in young unexpanded leaves of relatively high-sensitive plants was significantly higher than that of low-sensitive plants before and after treatment under inductive conditions. In conclusion, low-temperature-inducible changes in the flavonoid accumulation in petals was suggested to reflect a change in DvFNS expression occurring in the meristem prior to flower bud formation. This temporal DvFNS expression in young unexpanded leaves of ‘Nessho’ dahlia could be an insight for the selection and breeding of non-color fading plants.

Artificial Intelligence, or AI, is becoming increasingly prevalent in a wide variety of scientific fields. The recent progress in deep neural networks, or simply “deep learning”, in particular, has been remarkable, which is leading to the development of valuable technologies for various biological applications. Nevertheless, the application of these AI technologies in the field of horticultural science has not progressed. In the horticultural field, there is often a tendency to compare/compete with the accuracy (or ability) of AI and experts with long experience or existing systems, which may prevent the widespread adoption of AI technology in horticulture. The current evolving AI technologies go beyond mere prediction and diagnosis; through the application of “explainable AI” techniques, which can allow novel interpretations from a scientific perspective. It extends not only to conventional image analysis, but also to various data formats, including genetic sequences or any other numerical array data. Here, we introduce recent developments and evolution of AI technologies, mainly deep learning, in plant biology and horticultural science. Recent applications of convolutional neural networks (CNN) in image analyses allowed prediction/diagnosis of various invisible traits. Further combined application of explainable AI techniques and physiological assessments may spot features that potentially reveal the mechanisms of objective traits from a novel viewpoint. We also examined prospects for new applications of deep learning in horticultural science, such as for genetic factors or with new algorithms represented by Transformer.

The selection of appropriate pollinizer cultivars is essential for stable fruit production of Japanese apricot because this species has many self-incompatible cultivars. In this study, the chilling responses of flower buds during endodormancy and the heat responses of flower buds during ecodormancy were quantified as development rates (DVRs) in ‘Kotsubu-nanko’, ‘Hakuo’, and ‘NK14’, three pollinizer cultivars of the leading cultivar ‘Nanko’ in Wakayama Prefecture. Approximating functions of DVRs for both endodormancy release and ecodormancy release were obtained on the basis of chilling and heat exposure tests on young trees with various combinations of temperatures and periods. These analyses demonstrated that temperatures over 15°C were only effective for endodormancy release of ‘Hakuo’ buds. Compared with the buds of ‘Kotsubu-nanko’ and ‘Hakuo’, those of ‘NK14’ were less sensitive to 15–20°C during the ecodormancy stage. Blooming date prediction models for these cultivars were constructed using the DVR values. Then, the applicability of the three cultivars as pollinizers for ‘Nanko’ was evaluated based on whether their predicted blooming times overlapped with that of ‘Nanko’. The models were optimized by adjusting the threshold of blooming percentages and initial points of heat accumulation during ecodormancy release to achieve the smallest differences between predicted and observed blooming dates (root mean squared error = 3.72–5.90). Simulations under different temperatures revealed the most suitable pollinizer cultivar for ‘Nanko’ going forward. Our predictions indicate that, in the simulated warmer conditions, the blooming date of ‘Kotsubu-nanko’ will be delayed 10 or more days compared with that of ‘Nanko’, and larger differences between the blooming dates of ‘Hakuo’ and ‘Nanko’ will occur under lower and higher temperatures. The blooming period of ‘NK14’ was predicted to remain stably synchronized with that of ‘Nanko’ under a range of simulated warmer and colder temperature conditions. These results showed that ‘NK14’ is an appropriate pollinizer for stable fruit production of ‘Nanko’ in the future, and highlight the importance of blooming time assessments based on the temperature responses of flower buds.

Malformed flowers similar to super-double-flowers were observed in potted ‘Cherie’ carnation (Dianthus caryophyllus L.) plants. In the malformed flower (mlf) lines, most flowers were malformed at 15°C, but not at 20°C. Thus, we hypothesized that the malformation was due to a mutation associated with morphological responses to temperature. In this study, RNA-sequencing analysis of young flower buds and whole-genome re-sequencing of leaves were performed using wild-type (WT) and mlf plants to identify malformation-related candidate genes. The RNA-sequencing analysis revealed 691 significant differentially expressed genes (DEGs) between WT flower buds at 15 or 20°C and mlf flower buds at 15°C. The Gene Ontology (GO) analysis indicated that metal ion binding, transmembrane transport, and anaphase-promoting complex enriched GO terms in mlf, whereas translation and ribosome enriched GO in terms of WT. The Kyoto Encyclopedia of Genes and Genomes analysis revealed an increase in the expression of 9-cis-epoxycarotenoid dioxygenase (NCED), Pyrabactin Resistance 1-Like (PYL), and Calmodulin (CAM), but a decrease in the expression of Histone H4, in mlf. The fragments per kilobase per million reads (FPKM) values were used to select candidate malformation-related DEGs. Transcription factor genes, including WUSCHEL (WUS) and STERILE APETALA, were upregulated in mlf, whereas PISTILLATA-like protein, MADS-box protein CMB2, and F-box UNUSUAL FLORAL ORGANS were downregulated. Heat Shock Cognate 70 kDa (HSC70) and Temperature-induced lipocalin-1 were upregulated in mlf, but genes encoding histones and ribosomal proteins were downregulated. Moreover, NCED1, PYL8 and 9, and cytokinin-related genes were upregulated in mlf. Using whole-genome re-sequencing data, sequence variants were detected in the upstream regions and exons of WUS, HSC70-1 and 2, CAM7, and ribosomal protein-encoding genes. Furthermore, examination of the F₁ progeny derived from WT and mlf crosses with cultivars producing fertile pollen revealed a significant difference in the proportion of malformed flower phenotypes between WT and mlf regardless of temperature, suggesting that the malformed flower phenotypes of mlf can be inherited. Candidate genes associated with the temperature-dependent super-double-flower phenotypes were examined.

To develop novel humidification technology for strawberry production to achieve higher yields and improve fruit quality, four Japanese June-bearing strawberry cultivars were grown in a greenhouse with or without humidification treatment (HT) based on vapor pressure deficit (VPD). HT reduced VPD from transplanting to March, but did not affect the VPD condition from April to May. Soon after transplanting, HT enhanced plant growth and the daily leaf-emergence rate, and significantly advanced flower-bud emergence and first-fruit harvest for the first inflorescence for ‘Koiminori’, ‘Kaorino’, and ‘Saga i9’. However, HT significantly delayed flower-bud differentiation and first-fruit harvest of the second inflorescence of ‘Kaorino’ and ‘Yumenoka’. HT significantly increased the total weight of marketable fruit for ‘Koiminori’, ‘Kaorino’, and ‘Saga i9’. In addition, HT significantly increased the total fresh weight of marketable fruit harvested until December for ‘Koiminori’ and ‘Saga i9’. HT did not significantly affect the firmness of fruit skin (FFS), soluble-solid content (SSC), fruit acidity (FA), or SSC/acidity of ‘Koiminori’, ‘Kaorino’, and ‘Yumenoka’.