Picking excess berries is essential to obtain high-quality bunches of table grapes. However, this process requires significant labor within a short period, so labor-saving techniques are needed. We observed that the number of flowers per inflorescence was significantly reduced when 250 μL of 10%–15% trehalose was injected into the buds of ‘Shine Muscat’ using a microsyringe. Both the number of peduncles and the numbers of flowers on tip peduncles tended to decrease, showing that the synergistic effect of these two factors reduced the numbers of flowers in the inflorescences. However, a significant reduction in the number of flowers was observed only when trehalose was injected into buds with a vertical diameter of 10 to 15 mm, indicating that trehalose is effective only within a very limited time frame. To assess the degree of labor saving, we evaluated the time required for berry thinning by combining trehalose injection with two methods of cluster shaping: the conventional method and a labor-saving method. In the conventional method, we cut the peduncles with scissors and retained the main tip of the cluster at 4 cm, whereas in the labor-saving method, we cut the main axis of the rachis with scissors and used wing or lateral peduncle lengths of 4 cm. The average time required to pick berries from trehalose-treated grapes was significantly shorter (36.3 s) compared with untreated grapes. When scaled to 10 a (3,000 bunches), the combination of the conventional method and trehalose injection reduced the labor time required by approximately 40.3 h, while the labor-saving method combined with trehalose injection reduced labor time by approximately 100.3 h compared with conventional cultivation. The trehalose injection process required approximately five seconds per bud. Assuming injection of 6,000 buds on 3,000 shoots over 10 a, this would take an estimated 8.3 h. Thus, trehalose injection is an effective option even when accounting for the labor involved in the injection process. In addition, the trehalose injection did not have any adverse effects on the bunch quality. To develop a more effective method, further research is needed to elucidate the molecular mechanisms underlying the effect of trehalose on grape flower development.

Vernalization is a process in which plants achieve the competence to flower in the upcoming spring through exposure to long-term cold like winter. Unlike cold acclimation (short-term cold stimulus), vernalization is not immediately triggered by exposure to temporary low temperature. It seems likely that vernalization is triggered by low temperatures during winter that set up stable changes that last until the upcoming spring when they trigger floral transition. Over several decades, extensive studies have been conducted to elucidate the molecular mechanisms underlying the vernalization-mediated floral transition process using Arabidopsis thaliana (Arabidopsis) model plants, as well as crop plants. Comprehensive knowledge of the molecular mechanisms underlying vernalization-mediated floral transitions in the model plant Arabidopsis has helped us explore and reveal the molecular mechanisms controlling floral transitions in other plants, especially Brassica crops. This review highlights the current understanding of the molecular characteristics underlying vernalization-mediated flowering in Arabidopsis, as well as in several horticultural Brassica crop plants.

Epigenetics is defined as “the study of changes in gene function that are mitotically and/or meiotically heritable and do not involve a change in DNA sequence”. Epigenetic modifications include post-translational modifications of histones and DNA methylation. Changes in DNA methylation have been observed in response to environmental factors, with some epimutations being heritable across generations. Such epimutations may lead to alterations in plant traits and could be involved in natural selection or domestication. Furthermore, epigenetic transcriptional regulation serves as a crucial strategy for responding to various environmental conditions, including abiotic and biotic stress. In horticultural crops, this regulation is implicated in diverse biological processes, including agronomic traits such as hybrid vigor/heterosis, flowering time, bud dormancy, sex determination, fruit ripening, and anthocyanin accumulation. Recent advances in methods for analyzing epigenetic states, along with advances in sequencing technology, have enabled high-resolution and genome-wide studies in various horticultural crops. This review highlights the critical role of epigenetic transcriptional regulation in biological processes in horticultural crops and discusses the potential for artificially inducing epigenetic variation to enhance phenotypic diversity in horticultural crop breeding.