Akebia trifoliata is cultivated locally in few areas of Japan. Artificial pollination is considered indispensable for stable fruit production, as Akebia spp. exhibit self-incompatibility (SI). However, little is known about the reproductive physiology required for effective artificial pollination. In this study, we investigated the effects of self-pollen contamination on the fruit set of ‘Fuji Murasaki’ (A. trifoliata), one of the main lines in Yamagata Prefecture, Japan. Both the self- and cross-pollen tubes reached the base of the ovary and penetrated the ovules at 10 days after pollination, indicating that A. trifoliata exhibits late-acting SI. Self-pollination one day before cross-pollination completely inhibited fruit set, while self-pollination one day after cross-pollination did not inhibit fruit set in both 2016 and 2020, indicating interference in cross-pollination by self-pollen contamination. Fruit set rates for artificial pollination using a 1:1 mix of self- and cross-pollen were significantly lower than those that used non-contaminated cross-pollen in both 2016 and 2019, but were comparable when using a 1:1 mix of lycopodium powder and cross-pollen. The seed number of fruit resulting from mixed pollination was not significantly lower than that of fruit resulting from cross-pollination. Interestingly, 1:1 mixed pollination of self- and cross-pollen sometimes yielded abnormal fruits with an apex that remained pale and did not soften. These results suggest that excessive self-pollen contamination in artificial pollination may not be desirable for A. trifoliata fruit production.
Prunus (Rosaceae) includes many commercially important fruit crop species that exhibit self-incompatibility (SI), including sweet cherry (P. avium L.), Japanese apricot (P. mume Sieb. et Zucc.), Japanese plum (P. salicina Lindl.), apricot (P. armeniaca L.), and almond (P. dulcis [Mill.] D. A. Webb.). These species exhibit S-ribonuclease-based gametophytic SI, which prevents self-pollen tube growth in the pistil. The successful production of self-fertilized progeny accomplished by artificially overcoming the SI barrier has not been reported in Prunus, but self-compatible (SC) Prunus mutants with mutated pollen S determinant S haplotype–specific F-box (SFB) or pollen modifier M-locus encoded glutathione S-transferase-like (MGST) genes have been identified and used as SC cultivars and breeding stocks. In this study, we suppressed translation of SFB or MGST mRNA in self-pollen using antisense oligonucleotides to overcome the SI barrier in P. avium, P. mume, and P. salicina. Over the three years of the study, we obtained self-fertilized progeny of SI Japanese plum ‘Sordum’ only when SFB or MGST was knocked down. We also found that the average length of the self-pollinated pollen tube in the pistil of ‘Sordum’ was increased following treatment with an antisense oligonucleotide against SFB. This is the first report regarding the successful production of selfed progeny of Prunus obtained by disrupting SI. Our findings also provide evidence that the loss of function of SFB or MGST in Prunus pollen leads to SC.
To determine the effects of drought stress, especially light drought stress, on flower number in passion fruit, one-year-old passion fruit plants grown in 7.5 L plastic pots were subjected to different soil water content treatments, namely wetness, light drought, and heavy drought for two months. Average, maximum, and minimum soil water contents (v/v) were 44, 47, and 41% in the wetness treatment, 23, 40, and 11% in the light drought treatment and 11, 33, and 6% in the heavy drought treatment. Flower number decreased as the strength of drought stress increased, although the number of nodes and flower buds did not. Flowering periods were from June 27 to July 19 in the wetness treatment and June 26 to July 16 in the light drought treatment with three peaks around July 1, 6, and 13. In the heavy drought treatment, the flowering period was from July 11 to 18 with one peak. The flower bud number was not affected by drought stress. Light drought stress did not suppress vegetative growth, such as vine length, leaf number, leaf length, or photosynthetic rate, although heavy drought stress did. Stomatal conductance was suppressed by light drought only at 12:00PM and by heavy drought throughout the day. Leaf water potential was decreased by heavy drought at 3:00PM, but not by light drought. In the wetness and light drought treatments, visible wilting was not observed, and in the heavy drought treatment the plants wilted before irrigation, although they recovered about 15 min after irrigation. In conclusion, even light drought stress, which did not suppress vegetative growth, reduced the flower number in passion fruit. Drought stress suppressed flower bud development but not differentiation.
The pathogenic bacterium Pseudomonas syrinage pv. actinidiae causes bacterial canker disease, which is the most damaging disease afflicting kiwifruit (Actinidia chinensis). The most prevalent strain is biovar 3 (Psa3), which is highly pathogenic. Therefore, Psa3-resistant varieties of kiwifruit are urgently needed. A previous study reported that Actinidia rufa, a wild Japanese species related to kiwifruit, is highly resistant to Psa3. Genome-wide DNA markers may be useful to locate the loci that confer Psa3 resistance. Therefore, in the present study, we used published kiwifruit genome sequence information to design 1,101 simple sequence repeat (SSR) markers covering the entire kiwifruit genome in silico. We next examined DNA polymorphisms in more than 1,000 polymerase chain reaction products for potential use as SSR markers among A. rufa Fuchu and A. chinensis FCM1, a pollen-providing parent Fuchu A. chinensis male 1, and other kiwifruit cultivars in order to develop Psa3 resistant kiwifruit cultivars. We finally obtained 351 polymorphic markers, in the entire kiwifruit genome, which can be applied to produce next-generation kiwifruit cultivars, including Psa3-resistant cultivars.
Citrus nursery trees in California must be grown in insect exclusion facilities to protect them against Huanglongbing (HLB), a deadly disease caused by Candidatus liberibacter spp. and spread by the Asian citrus psyllid (Diaphorina citri). Faster year-round propagation is critical for citrus nurseries to offset their investment in new exclusion facilities, but nurseries currently face serious problems in terms of poor bud push and slow scion growth in fall-budded, container-grown trees. The purpose of this study was to explore the effect of supplemental LED lighting techniques on the photosynthesis and total non-structural carbohydrate (TNC) partitioning within citrus trees that is responsible for growth cessation during the fall. A total of 72 trees of Carrizo citrange rootstock with and without Clementine Mandarin scions, were placed in growth chambers during four photoperiods: T1, 10 h LED + 4 h extension of day length (EoD, 10 μmol·m−2·s−1); T2, 10 h LED with 1 h supplemental night interruption (NI); T3, 10 h LED with 10 h supplemental far-red (FR) lighting; and T4, controls (10 h LED). The LED light spectrum was adjusted to 90 red and 10 blue ratios. The trees were grown in the growth chambers at 21/13°C day/night temperatures and 80% RH for 12 weeks. Trees were harvested and separated into leaves, stems, and roots at the end of the experiment. Different tissues were oven dried, ground and analyzed for TNC. The results showed that NI and EoD resulted in significantly higher plant growth. Both NI and EoD allowed trees to accumulate lower levels of carbohydrates in the root system, thereby decreasing the root: shoot ratio. NI and EoD trees had lower root: shoot ratios for TNC than control and FR trees in both budded and unbudded trees, suggesting the storage of reserves in roots can be enhanced during shorter day length. Results also showed that NI and EoD photoperiods triggered phytochrome with low light intensity, which in turn induced a long day effect and further translocation of reserves from roots to aboveground parts to improve vegetative growth.
This study investigated anthocyanin accumulation, sugar contents, and endogenous hormone contents in the berry skin, as well as the expression of genes related to anthocyanin and abscisic acid (ABA) synthesis and metabolism, using grafted ‘Ruby Roman’ berries on the rootstocks of ‘Kober 5BB’ [5BB(2x), a semidwarf rootstock], ‘Hybrid Franc’ [HF(2x), a vigorous rootstock], and their colchicine-induced autotetraploids [5BB(4x) and HF(4x)]. Rootstock had significant effects on the total content, but not on the composition, of anthocyanins. The berries on 5BB(4x) rootstock, where the grapevine showed less vegetative growth, had higher anthocyanin content during the ripening process, and also had higher sugar and ABA contents around véraison. ABA, indole acetic acid (IAA), and cytokinins showed synchronous changes during berry development: they had the lowest levels at pre-véraison, and their metabolic pathways were accelerated after véraison. Furthermore, they all tended to be higher on 5BB(4x) than on the other rootstocks. Since the expression levels of most of the ABA biosynthesis-related genes did not show a corresponding increase with the contents of ABA and ABA-glucosyl ester (ABA-GE), it is considered that the increase in ABA content after véraison may be mainly due to the decrease in catabolism and/or exogenous import from other organs. This study provides an overview showing the dynamic changes and relationship of three phytohormones during the ripening of grape berries grafted on different rootstocks, and explores the mechanisms regulating ripening.
The growth and quality of the fruit from adult ‘Fuyu’ and ‘Hiratanenashi’ Japanese persimmon (Diospyros kaki Thunb.) trees that were grafted onto D. kaki seedlings (S), Rootstock-a (R-a), ‘MKR1’, and own-rooted (O-R) trees planted in February 2003 were observed from 2015 to 2021, when almost all of the trees entered stable, high-productive phases and the fruit quality was stable. The trees that were grafted onto ‘MKR1’ were still dwarfed but produced fruit efficiently. After disbudding took place, in the first half of stage I of the double sigmoid growth curve there was a certain period of time when the fruit of the ‘Hiratanenashi’ trees that were grafted onto ‘MKR1’ was lighter than the trees that had been grafted onto S. However, in the second half of stage I, the fruit of the former was heavier than that of the latter, and the flesh cells of the former were larger than that of the latter. In stage II and III, the fruit of the latter grew faster and became significantly heavier just before the harvest. The fruit growth of the ‘Fuyu’ trees that were grafted onto R-a was retarded compared to the growth of trees that were grafted onto ‘MKR1’ throughout most of the growing period. Heavy disbudding (HD) effectively increased the fruit weight of the ‘Hiratanenashi’ trees that were grafted onto ‘MKR1’ in a certain time period in stage I and in stage III compared to normal disbudding. HD also improved the fruit growth of the ‘Fuyu’ trees that were grafted onto ‘MKR1’, although this was not as effective as the ‘Hiratanenashi’ fruit growth. The weight of the harvested ‘Fuyu’ trees’ fruit increased in the following order: R-a, ‘MKR1’, O-R, and S. The ‘Hiratanenashi’ trees that were grafted onto ‘MKR1’ had the lightest fruit among the rootstocks, but the HD treatment for the trees that had been grafted onto ‘MKR1’ increased the fruit weight, and the difference disappeared. The soluble solids concentration of ‘Fuyu’ fruit was the highest in ‘MKR1’ and the lowest in R-a. ‘Hiratanenashi’ fruit had the highest concentration of soluble solids in S and the lowest concentration in O-R. The level of firmness of ‘Fuyu’ fruit flesh was the hardest in ‘MKR1’ and the softest in R-a, whereas the level of firmness of ‘Hiratanenashi’ fruit was the same among the rootstocks. Although the a* value of ‘Fuyu’ fruit skin color was the same among the rootstocks, the a* value skin color of ‘Hiratanenashi’ fruit was the highest in ‘MKR1’ and R-a and the lowest in S. These results suggest that the persimmon rootstock partly affects growth and quality of the fruit, although there are differences in the reactions between scion cultivars.
In the replanting of Japanese pear, the growth of young trees after replanting is often suppressed due to soil sickness syndrome and white root rot. Pre-planting soil disinfection by hot water drip irrigation (HWD) treatment was developed as a control technique for white root rot. In addition, it is also expected to reduce the risk of soil sickness and promote tree growth. We therefore investigated the HWD treatment of pre-planting soil to promote the growth of young trees and obtain high yields at an early stage after replanting Japanese pear. HWD treatment of the pre-planting soil accelerated the growth of young trees in the first two years after planting and increased the yield in the third year compared to untreated soil. The HWD and water treatments of soil lowered the risk of soil sickness syndrome, suggesting that washing out growth-inhibiting substances with water promoted the growth of young trees. The HWD treatment flushed out nitrate-nitrogen from the soil and temporarily increased ammonia nitrogen due to decreased nitrifying activity one day after treatment. However, the change in nitrogen in the soil did not significantly affect growth, and the pH of the soil did not change significantly before and after the treatment. This suggests that the growth-promoting effect was not solely due to changes in soil chemistry, but rather due to the reduction in the risk of soil sickness. These results suggest that HWD treatment of pre-planting soil effectively reduces the risk of soil sickness and promotes the growth of young trees during the replanting of Japanese pear.
Artificially occurring parthenocarpy can be induced by exogenous application of plant hormones and is useful in the fruit production of many fruit crops and fruit trees. In cucumber (Cucumis sativus L.), a model species in the Cucurbitaceae family, the plant hormones auxin, gibberellin, cytokinin, and brassinosteroids are known to induce parthenocarpy. In tropical squash (Cucurbita moschata L.), synthetic auxins are known to induce parthenocarpy, but the effects of gibberellin, cytokinin, and brassinosteroids are still unknown. In addition, there are few published reports on the quality of parthenocarpic fruits induced by plant hormones in tropical squash, and the effects of these hormones remain largely unknown. In this study, we examined the effects of gibberellin, cytokinin, and brassinosteroids on the parthenocarpy of tropical squash and characterized the parthenocarpic fruits induced by the plant hormones. First, we evaluated fruit set and development in unpollinated fruits of ‘Kogiku’, a tropical squash cultivar, treated with gibberellic acid (GA3), a synthetic cytokinin-like substance, N-(2-chloro-4-pyridyl)-N′-phenylurea (CPPU), and brassinolide (BL). CPPU promoted parthenocarpy, but GA3 and BL did not, showing that cytokinin works as an important factor for parthenocarpy in tropical squash. Next, we investigated the quality of parthenocarpic fruits from ‘Kogiku’ induced by a synthetic auxin, 1-naphthylacetic acid (NAA), and CPPU. Total soluble solids and myo-inositol of NAA-treated parthenocarpic fruit were higher than those of pollinated fruits, whereas fructose of NAA-treated parthenocarpic fruit and fructose and glucose of CPPU-treated parthenocarpic fruits were significantly lower than those of pollinated fruits. These results showed that parthenocarpy of tropical squash induced by auxin and cytokinin had differing effects on fruit quality.
Onion (Allium cepa L.) is one of the most important vegetable crops in the world, and its cultivation is roughly divided into two types: autumn- (overwinter) and spring-sowing. In this study, we compared the changes in plant growth and bulb development of four short-day and intermediate-day onion cultivars under two years of varying environmental conditions to understand autumn-sowing cultivation and growth characteristics. A comparison of the growth parameters of the four cultivars throughout the growth period revealed that the increase in total leaf number and area, and plant height were almost completely inhibited in winter. In spring, these growth parameters increased rapidly in the early maturing cultivars and reached a plateau depending on the cultivar’s maturity type, as previously shown in spring-sowing cultivation. It is known that AcFT1 and AcFT4 play a key role in the bulb development of cultivated onions. Therefore, we conducted expression analysis of these genes for the four cultivars grown in the field and confirmed that AcFT1 was expressed following the maturity, irrespective of cultivation methods. We also analyzed AcGI expression in leaf blades, and a certain relationship between changes in bulb development and AcGI expression was observed. Correlation analysis of AcFT1 expression and total leaf number and area was conducted, and strong positive correlations were observed. In conclusion, our study demonstrated genetically that leaf number and area are important for inducing onion bulb development.
Two chili pepper (Capsicum annuum L.) cultivars ‘Super Hot’ and ‘Num Khao’ grown under field conditions in Thailand were sprayed with 0 (distilled water, control), 25, 50, 100, and 200 ppm chitosan after one week from transplanting and weekly thereafter for five weeks. Chitosan spray improved vegetative growth of both cultivars as measured by increased canopy size. It also increased the plant height of the ‘Super Hot’ cultivar and reduced leaf curl incidence in the ‘Num Khao’ cultivar. Leaf size and chlorophyll content were not significantly affected. Fruit were harvested from cultivars at the commercial maturity stage; that is, the red-ripe stage for ‘Super Hot’ and light green stage for ‘Num Khao’. From the four harvests at weekly intervals, chitosan treatment increased the ‘Super Hot’ yield because of greater fruit production and increased fruit size and there was a higher number of fruit per plant produced by the ‘Num Khao’ cultivar. Fruit color (L*, a*, b*, and sensory color) was not affected, but overall acceptability increased in response to chitosan spray due to improved size and quality of the ‘Super Hot’ cultivar and improved appearance, size and glossiness of the ‘Num Khao’ cultivar. Chitosan at 50 ppm appeared to be the optimum concentration to induce the above effects in both cultivars.
Postharvest blossom-end enlargement (BEE) in summer cucumber has a serious economic effect in Japan. Previous studies suggested that BEE is influenced by cultivation conditions and temperature during transportation. In this study, the relationship between postharvest BEE and growth parameters in plants under various sink–source balances created by defoliation and fruit thinning was determined using a growth analysis technique. Cucumber (Cucumis sativus L. ‘Taibo I’) seedlings were transplanted into an outdoor field at Ibaraki University in 2019, and the harvested fruits were stored in plastic bags at 27°C. The occurrence of BEE, which was scored six days after harvest, was positively correlated with the field air temperature and cumulative duration of sunshine exposure from flowering to harvesting. Furthermore, high temperatures and extended sunshine exposure reduced the time from flowering to harvesting. However, excessive defoliation reduced BEE occurrence, most likely because of the increased time from flowering to harvesting, suggesting that early fruit maturation may be one of the causes of BEE. Therefore, principal component analysis was performed to understand the relationship between growth parameters and the occurrence of BEE in cucumber. The occurrence of BEE increased when the sink–source balance was inclined towards the source. Collectively, these findings indicate that high temperatures, extended exposure to solar radiation, and large leaf area with respect to the number of fruit set increase the occurrence of BEE, with pre-harvest fruit maturity probably related to its onset.
We investigated the effects of CO2 enrichment on photosynthesis, growth, and dry matter accumulation in the Oriental hybrid lily ‘Siberia’. The photosynthetic rate increased as the CO2 concentration was elevated compared to the ambient level. The increase in the photosynthetic rate was greater in the low concentration range and lower in the high concentration range. The relationship between the light intensity-photosynthetic rate and temperature-photosynthetic rate was investigated under different CO2 concentrations. The entire light-photosynthesis and temperature-photosynthesis curves moved toward a considerably higher photosynthetic rate when the CO2 concentration was increased from 380 ppm to 1000 ppm. In contrast, when the CO2 concentration was increased from 1000 ppm to 2000 ppm, the increase in the entire light-photosynthesis curve was small. The relationship between the CO2 concentration and the maximum temperature point of the photosynthetic rate was unclear. We also cultured ‘Siberia’ lily plants with and/or without CO2 enrichment (1500 ppm) altered before (the early stage) and after (the late stage) the visible flower bud stage. The CO2 enrichment increased dry weights dry weight/fresh weight ratios of whole plants, and individual parts at flowering, resulting in improved cut flower quality and enlargement of the mother bulb and daughter bulblets. The effective period of CO2 enrichment was after the visible flower bud stage. In cases where CO2 enrichment was effective for dry matter accumulation, the dry matter distribution ratios of the mother bulb and daughter bulblets to the whole plant were high, and those of the leaves, stem, and flower buds were low. The relative growth rate and net assimilation rate from planting to the flowering stage were increased with CO2 enrichment applied after the visible flower bud stage, indicating that the dry matter accumulation and photosynthesis were enhanced. Finally, the issues that need to be addressed for applying practical CO2 enrichment technology to various lilies are discussed.
Cut dahlia (Dahlia Cav.) flowers have recently become popular, but their marketability has been limited due to their poor vase life. The purposes of this study were to clarify the roles of leaves and inflorescences in the senescence of cut dahlias and to discuss the sink-source relationship between vegetative organs and inflorescences. The leaf life was maintained much longer (16.7 days) than the inflorescence life (7.4 days). The inflorescence life was not affected by removal of leaves, while leaf life was prolonged (19.6 days) by removal of inflorescences. Sucrose, glucose, fructose and small quantities of myo-inositol were detected in florets, and in addition to these sugars, nystose and 1-kestose were detected in stems and leaves. Total sugar levels of the middle florets (14.5 mg·g−1 FW on day 0) declined rapidly before their senescence. Total sugar levels of leaves (20.5 mg·g−1 FW on day 0) and stems (19.0–22.5 mg·g−1 FW on day 0) also decreased gradually during the postharvest period, but the levels decreased more slowly in deflowered cut stems. Sugar leakage from stem bases into vase water occurred during the initial few days. Removal of inflorescences increased sugar leakage significantly and promoted callus formation on the stem base. From these results, the inflorescence is considered to be a strong sink for carbohydrates, and stems and leaves serve as source organs. Heat girdling applied to the flower necks and petioles, also increased sugar concentrations of stem bases, thus resulting in higher sugar leakage and callus formation, although both heat girdling treatments shortened the leaf life. The sharp decrease in sugar levels of florets and an insufficient sugar supply are considered to be responsible for the short vase life of cut dahlias. It is suggested that these effects might be partly due to the blockage of sugar flows into petals through abscission layer development in the petal-ovary boundaries. Based on these results, we illustrate the senescing process of cut dahlia flowers in relation to sugar dynamism.