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Reproductive biology of fruit and nut tree crops

Special Issue:
Reproductive biology of fruit and nut tree crops

Editor: Chitose Honsho and Tomoya Esumi
April 2022

The Japanese Society for Horticultural Science has published special issues of The Horticulture Journal (Hort. J.) to further enhance the value and attractiveness of this journal. The theme of the fourth special issue is “Reproductive biology of fruit and nut tree crops.”

Reproductive development in plant species involves a series of dynamic and interesting biological events. In fruit and nut tree crops, reproductive events are essential for fruit and nut production because the reproductive organs develop into edible parts and are a source of products. A comprehensive understanding of reproduction in fruit and nut tree crops will lead to the improvement of fruit productivity, the development of seedless fruit, the practical and technical improvement of pollination and fertilization, and others. On the other hand, some fruit tree crops have inherent barriers that interrupt fertilization for hybrid formation, such as self-incompatibility and male or female sterility, which are intriguing topics in the basic science of plant reproduction, and an understanding of those topics will contribute to the breeding and creation of new cultivars. In addition, ongoing climate changes, namely, global warming, have affected reproductive processes in perennial trees, ultimately influencing fruit and nut production. In this regard, the study of the physiology of reproductive development has become increasingly important in recent years from the perspective of coping with such environmental changes.

Research of the reproductive system and process in fruit and nut trees has long been pursued and remains active as one of the central topics in horticultural research. This special issue has been launched for the purpose of disseminating recent research outcomes from society members to the academic community of horticulture and fruit and nut industries worldwide.

 

REVIEW
Norimitsu Tanaka, Masato Wada

Pages: 91 (2): 131–139. 2022.|doi: 10.2503/hortj.UTD-R018

Abstract

Parthenocarpic apple cultivars have been recognized with simultaneous homeotic floral organ mutations. The mutations included replacements of petals to sepals and stamens to carpels, which were same as the class B mutations of floral organs from Arabidopsis and snapdragon. For apple, the parthenocarpy and class B mutations were tightly inherited and MdPISTILLATA (MdPI) gene deficiency caused homeotic mutations. However, the relationship between the suppression of MdPI and parthenocarpy was unclear. Transgenic apples with suppressed MdPI expression using an anti-sense or co-suppression method were found to have the same homeotic floral organ mutations as parthenocarpic cultivars. Further, the transformants with co-suppression showed parthenocarpy and overexpression of MdPI in fruits prevented normal fruit growth. Other apple MADS genes were analyzed for parthenocarpy. MdMADS13 is classified as another class B gene, which plays a role in floral organ formation together with MdPI. In addition, MdMADS1/8 and MdMADS9 are classified as class E genes, which are could function like SEP1 and 2 genes from Arabidopsis. The MdMADS1/8 and MdMADS9 gene-suppressed apple transformants showed strong inhibition of fruit enlargement, supporting the idea that MdMADS1/8 and MdMADS9 contribute to hypanthium development. It is possible that the MdPI, MdMADS13, MdMADS1/8, and MdMADS9 proteins formed a heterotetramer as a transcriptional regulator and were involved in fruit development. Other plant species such as tomato and grape also showed the respective class B genes affected fruit development. The suppression of tomato class B genes led to class B floral organ mutations and parthenocarpy, and a grape mutant with class B gene expression ectopically inhibited fruit flesh development. Both class B genes seemed to prevent fruit development similar to the apple MdPI. This suggests that the class B genes play not only a role in forming the identities of petals and stamens, but also a pivotal role in fruit development.


ORIGINAL ARTICLE
Kyoka Nagasaka, Hisayo Yamane, Soichiro Nishiyama, Shu Ebihara, Ryusuke Matsuzaki, Masakazu Shoji, Ryutaro Tao

Pages: 91 (2): 140–151. 2022.|doi: 10.2503/hortj.UTD-332

Abstract

Pollination is an important factor affecting fruit development in highbush blueberry (Vaccinium corymbosum L.). In general, planting several different blueberry cultivars increases the chances of cross-pollination and ensures high-quality fruit production. However, little is known about the effects of the pollen source on fruit development in blueberry. The aims of this study were: 1) to understand the effects of the pollen source on fruit size and quality; and 2) to explore the mechanisms underlying fruit development affected by the pollen source. We first characterized the pollination effect on fruit development using 14 different pollination combinations for several years and found that the number of mature seeds and fruit size differed significantly among the fruit pollinated by different pollen sources. Significant correlations between the number of mature seeds and fruit size were found in most combinations, whereas the number of mature seeds was not correlated with other fruit quality parameters such as sugar concentration. Our results and those of previous reports showed that the number of mature seeds, which was influenced by the pollen source, was a primary determinant of fruit size. Time-course observation during fruit development revealed that fruit weight and cell size significantly differed between self-pollinated and cross-pollinated fruit from 30 days after pollination onwards. To explore the molecular mechanisms underlying berry growth affected by developing seeds, we compared gene expression changes between self-pollinated and cross-pollinated fruit. Transcriptome analysis of fruit at 10 days after pollination suggested that auxin signaling pathways were enhanced in cross-pollinated fruit compared with self-pollinated fruit. We thus hypothesize that activated auxin signal transduction underlying early stage seed and fruit development may promote fruit cell enlargement during the early stage of fruit growth in highbush blueberry.


ORIGINAL ARTICLE
Panawat Sikhandakasmita, Ikuo Kataoka, Ryosuke Mochioka, Kenji Beppu

Pages: 91 (2): 152–156. 2022.|doi: 10.2503/hortj.UTD-341

Abstract

In protected agriculture, optimum temperature management is crucial for enhancing fruit productivity and maintaining cost-effective production. The aim of the present study was to investigate the effects of temperature on peach fruit development and quality. Container-grown ‘KU-PP2’ peach trees grafted on low-chill peach rootstocks were cultivated under controlled conditions at different temperatures (20, 25, and 30°C) during fruit development for two years (2020 and 2021). Fruit growth rates were calculated by measuring fruit diameter every 3 d from fruit setting to first harvest; fruit quality and phytochemistry were analyzed at harvest. Growing temperature markedly affected fruit growth, maturation, and fruit quality. The development of fruit in all treatments exhibited double sigmoid growth curves that included three stages (S1, S2, and S3). Fruit growth rate during S1 and S2 stages was increased, and fruit development period was significantly shortened with an increase in temperature. Contrary to the duration of S3, which was longer at higher temperatures, fruit grown at a high temperature (30°C) ripened by 12–18 days earlier than those grown at low-temperature regimes. In addition, high-temperature conditions were also associated with reduced fruit quality (size, weight, and sweetness), but enhanced development of red coloration. Therefore, even though high-temperature conditions can accelerate early fruit expansion and hasten fruit maturity, such conditions also have negative effects on important agronomic fruit traits.


ORIGINAL ARTICLE
Soichiro Nishiyama, Daisuke Yoshimura, Akihiko Sato, Keizo Yonemori

Pages: 91 (2): 157–168. 2022.|doi: 10.2503/hortj.UTD-333

Abstract

Gibberellins are widely used to induce seedlessness in table grape production, but are not effective for every cultivar or developmental stage. In order to characterize the potential physiological mechanism behind gibberellin-induced seedlessness, we conducted tissue-specific transcriptome analysis of ovules and ovaries from cultivars with different levels of receptiveness to seedlessness induction. GA3 treatment at full bloom highly induced gibberellin signaling and various phytohormone signaling pathway genes in ovules at two days after treatment, but had less effect in ovaries, which suggests that GA3 directly affects seed development. During the development to six days after GA3 application, cell cycle-related genes in the ovules were markedly downregulated, indicating that this may be related to ovule abortion induction. The marked transcriptomic responses were largely absent in a cultivar with low receptiveness to gibberellin-induced seedlessness, suggesting a crucial role for the observed tissue-specific responses in the successful induction of seedlessness by GA3 application. Collectively, our transcriptome analysis highlights distinct tissue-specific reactions to GA3 during early berry development, providing important insights for the successful production of seedless berries by gibberellin application.

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