The very young seedlings of trifoliate orange, and its hybrids with trifoliate leaves as a marker, are usually used as a rootstock for in vitro and in vivo micrografting of citrus to eliminate viruses in spring in temperate regions. In tropical and subtropical regions or in summer, however, the production and use of trifoliate orange seedlings is difficult. Therefore, it is necessary to establish suitable micrografting using efficient Citrus seedlings adapted to these regions and summer. In decapitated seedlings for micrografting, adventitious shoots on the cut end of the epicotyls and shoots from cotyledon axillary buds are often formed. Hence, the potential for adventitious shoot formation and cotyledon axillary shoot formation was firstly studied with decapitated seedlings from 11 Citrus accessions and one Poncirus accession as a control. Mature seeds of the 12 accessions were germinated in vivo and seedlings of various ages (2-, 4-, and 8-week-old, 4-month-old and 8-month-old after germination) were decapitated at three (lower, middle, and upper) positions on the epicotyls. Adventitious shoot formation decreased with increases in the age of seedlings decapitated at eight weeks or 4 months after germination. The percentage of decapitated seedlings forming adventitious shoots was different in different accessions ranging from 0% to 100%, and increased with increases in decapitation height in the epicotyls. It was estimated from these results that 2-week-old seedlings of Natsudaidai, Shiikuwasha, ‘Hirado-buntan’, ‘Variegated Daidai’, and trifoliate orange ‘Flying Dragon’ had higher potential to support the initial growth of adventitious shoots, and cotyledon axillary shoots than the others, and that decapitation at the upper one-third and middle of epicotyls resulted in higher adventitious shoot formation than the lower one-third. In in vivo micrografting of satsuma mandarin on the seedlings of these accessions, Natsudaidai, ‘Hirado-buntan’, and ‘Variegated Daidai’ seedlings resulted in high micrografting success rates, whereas ‘Kabusu’, ‘Flying Dragon’ and Shiikuwasha seedlings resulted in very low success rates. The success rate decreased with increases in seedling age. It has become clear from these results that there is no relationship between the potential for shoot formation and micrografting success and that the 2-week-old seedlings of Natsudaidai, ‘Hirado-buntan’ and ‘Variegated Daidai’ are efficient rootstocks for micrografting.
Brassica napus L. is one of the most important oilseed crops in the world. The flower stalks (lateral shoots) of the leafy vegetable B. napus landrace, commonly known as norabona, are consumed for nutritional purposes and these plants are grown in the Kanto region of Japan. In the present study, we revealed the diversity of norabona at genotypic and phenotypic levels. Samples were collected from four different areas in the Kanto region of Japan and comprised other leaf vegetable landraces (kakina; B. napus and komatsuna; B. rapa). Phenotypic traits were assessed by investigating six morphological traits and five compositions for flower stalks. Principal component analysis in multivariate analysis demonstrated that the 20 norabona and kakina samples in the present study could be separated into three clusters. Genotyping using a total of 24 simple sequence repeat markers and Nei’s matrix genetic distances and neighbor-joining clustering method led to the partitioning of 23 samples into three groups and komatsuna. The genotypic Group 1b comprised the largest number of norabona samples; the farthest geographic distance was observed in genetically close pairs. On the basis of our results, we concluded that (1) the norabona population in Japan is phenotypically diverse and that (2) this population is not genetically identical, but consists of different genotype subpopulations that are geographically not divergent.
The translocation of calcium (Ca) within the tomato plant and the causes of Ca deficiency, a factor associated with blossom-end rot (BER) in fruit, are still a matter of conjecture. The objective of this study was to determine the effect of defoliation on BER incidence and Ca transport into different size tomato fruit cultivars. Four experiments were conducted. The start and end dates for each experiment were; 14 March–2 May, 22 July–23 August, 30 August–7 October 2017, and 20 May–25 June 2018, for experiments 1, 2, 3, and 4, respectively. Five tomato cultivars including one large (‘Momotaro fight (MF)’, ≥ 200 g), three medium (‘Lui 60 (L60)’, ‘Tio cook (TC)’, and ‘Cindy sweet (CS)’, 30–80 g), and one small (‘Pepe (PP)’, ≤ 20 g) fruit cultivars, respectively, were grown under moderate water stress controlled by a combination of root zone restriction and solar mediated fertigation. Leaf area of plants was reduced by 20–30% by removing alternate leaflets on all leaves. Defoliation significantly reduced BER in all experiments. In experiment 4, no BER was observed in defoliated plants of L60 and PP, and in MF and TC, BER incidence decreased to a quarter of the control. Defoliation increased the fruit growth rate (FGR) in experiment 1, in which the temperature was the lowest, by a ratio of 1.42 and by 1.39 in experiment 4, in which the radiation was strongest and day length longest. Defoliation increased the rate of daily Ca transport into fruit (CTR) in MF, L60, TC, CS, and PP by average ratios of 1.64, 1.55, 1.35, 1.30, and 1.13, respectively. The increase in CTR in defoliated plants was highest in experiment 4 with a ratio of 1.68 followed by 1.37, 1.33, and 1.28 in experiments 1, 3, and 2, respectively. Defoliation increased both FGR and CTR and there were significant linear relationships between them. However, the degree of increase was larger in CTR than that in FGR, especially in the BER-sensitive large fruit cultivar MF, and defoliation increased the total Ca concentration in fruit accordingly. We conclude that under moderate water stress by root zone restriction and certain other BER inductive conditions, defoliation could be a promising approach to reduce BER incidence by improving Ca nutrition in susceptible large fruit cultivars.
Anthocyanin in pepper is beneficial as a food antioxidant compound and as a pigment for ornamentals, while unexpected anthocyanin accumulation in fruit, known as black spots, reduces the commercial quality of some cultivars. Previous studies demonstrated that the Anthocyanin (A) locus determines the anthocyanin accumulation in pepper fruits, and an MYB transcription factor, CaMYBA, was found to be located near the A locus. However, the causal gene sequence of the A locus has not yet been identified. With progress regarding genome information in pepper, two other homologous MYB genes were found to be located near CaMYBA, and they are also considered to be candidate genes for the A locus. In this study, we attempted to identify the causal gene sequence of the A locus by performing linkage analysis, genomic sequence analysis, and gene expression analysis of the three candidate MYB genes. A crossing experiment between pigmented ‘Peruvian Purple’ and non-pigmented cultivars confirmed that anthocyanin accumulation in the pigmented cultivar was controlled by a single locus. Gene expression analysis demonstrated that a basic helix-loop-helix transcription factor, CaMYC, and CaMYBA were expressed abundantly in pigmented cultivars, but the other two MYB genes were not. Genotyping of the F2 population derived from the cross demonstrated that the anthocyanin accumulation phenotype was highly linked to CaMYBA, but not to CaMYC. The DNA sequence of CaMYBA in pigmented cultivars had an insertion of a 4.3 kb retrotransposable element LINE-1 in the first intron, but that of non-pigmented cultivars did not. No pigmented cultivar-specific sequence was found in the promoter region of CaMYBA. Therefore, it was suggested that CaMYBA, but not the other two homologous MYB genes, is the A locus gene, and insertion of LINE-1 in CaMYBA appeared to be important for the regulation of anthocyanin accumulation, although the mechanism by which the LINE-1 insertion induces CaMYBA expression is unknown.
Dianthus japonicus Thunb. (D. japonicus) is a biennial with promising floricultural traits, but its commercial appeal is limited by the long time between propagation and flowering. We assessed the effect of juvenile phase, vernalization, and photoperiod on flowering of D. japonicus. Plants were grown in a plug until they had acquired nine, 14, or 16 leaf pairs, and then exposed to a vernalization period of 0, 3, 6, or 12 weeks at 5°C. At the end of the vernalization period, plants were transferred to either long-day treatment or short-day treatment for 10 weeks. In D. japonicus, the numbers of new nodes and leaves were correlated with the vernalization period. Plant height was correlated with the number of leaf pairs. As the vernalization period lengthened, the plants produced more nodes and leaves regardless of their growth stage. The maximum plant height increase was over 24.7 cm in the plants that had 16 leaf pairs at 10 weeks after the start of the photoperiod treatment, regardless of the photoperiod. Plants with 14 or 16 leaf pairs and a vernalization period of 12 weeks flowered regardless of photoperiod treatment. None of the plants that had been vernalized for less than 12 weeks flowered or produced flower buds. We noted a significant difference in the flowering response among plants based on the number of leaf pairs and vernalization period. We conclude that D. japonicus plants must form 14 to 16 leaf pairs before they can respond to vernalization and require at least 12 weeks of vernalization before flowering. This species has a qualitative response to vernalization and is day-neutral.
In this study, we performed intergeneric crosses between Argyranthemum frutescens (L.) Sch. Bip. and seven perennial species of closely related genera [Artemisia absinthium L., Chrysanthemum lavandulifolium (Fisch. ex Trautv.) Makino × Chrysanthemum × morifolium Ramat., Dimorphotheca sinuata DC., Osteospermum ecklonis (de Candolle) Norlindh, Pericallis hybrida B. Nord., Rhodanthemum gayanum (Cross. & Durieu) B.H. Wilcox, K. Bremer & Humphries., and Rhodanthemum hosmariense (Ball) B.H. Wilcox, K. Bremer & Humphries.]. Using an embryo culture technique to generate intergeneric hybrids, we produced two putative hybrids from the crosses between A. frutescens and R. gayanum. In the putative hybrid derived from the cross between A. frutescens ‘Brilliant rouge’ × R. gayanum ‘Elf pink’, its ligulate flower color was similar to the ‘Brilliant rouge’ seed parent while the composition and total amount of anthocyanidins and/or leucoanthocyanidins were different. In the putative hybrid derived from the cross between A. frutescens ‘Sunday ripple’ and R. gayanum ‘African eyes’, its ligulate flower color differed from those of the parents. The ligulate flowers of the parents were white and produced no anthocyanidins, whereas the putative hybrids had light pink ligulate flowers and produced three anthocyanidins pigments [pelargonidins (including pelargonidin and/or leucopelargonidin), cyanidins (including cyanidin and/or leucocyanidin, peonidin), and delphinidins (including delphinidin and/or leucodelphinidin, malvidin)]. In addition, the cleaved amplified polymorphic sequence (CAPS) markers (Afl II) developed in this study confirmed that the putative hybrids were intergeneric hybrids of A. frutescens × R. gayanum. Therefore, these CAPS selection markers can be used to determine whether plants resulting from crosses are hybrids.
The development of new Anthurium cultivars relies on efficient micropropagation, which is highly dependent on genotypes, to provide enough young plants for cultivation. Microbial contamination is the critical factor for successful initiation of aseptic culture of Anthurium cultivars. The aims of this study were to investigate surface disinfection with either sodium hypochlorite or a fungicide Plant Preservative MixtureTM (PPM), and supplemental PPM in the medium to evaluate their effect on reducing contamination and tissue browning. Next, a liquid suspension culture system was developed to regenerate the adventitious shoots efficiently in a short time for subsequent establishment of young plantlets for transplanting. Disinfecting newly developed leaves of ‘Kaohsiung No. 1’ with 0.6% sodium hypochlorite was more effective than other disinfection treatments even though only 5% of leaf explants produced callus. However, disinfecting the leaves of ‘Kaohsiung No. 2’ with 0.15% sodium hypochlorite was more effective than other treatments, with a callus induction rate up to 100%. No callus was induced on ‘Orange Hot’ at any hypochlorite concentration. Disinfection using PPM could reduce the contamination rate. By supplementing 0.01% PPM to the culture medium, the callus induction rate of ‘Kaohsiung No. 2’ was up to 55%, and the browning rate was lower than the control with hypochlorite disinfection. However, surface disinfection using 25% and 50% PPM did not lead to any callus formation in any of the three cultivars. Calluses of A. ‘Kaohsiung No. 2’ induced after 60 days of culture were transferred onto liquid suspension after 60 days for further proliferation of adventitious shoots and subsequent plantlet regeneration. Young plantlets could be successfully transplanted in peat moss and later flowered within 16 months.
The aim of this study was to develop efficient night cooling technology to produce high-quality carnation cut flowers. The effects of temperature and timing of night cooling treatments (applied using a heat pump) on the flowering time and quality of cut flowers were investigated for standard type carnation flowers grown in a greenhouse in hot conditions. In the first experiment, rooted cuttings of the carnation ‘Exceria’ were planted in a greenhouse on July 6, 2012. Night cooling treatments at 18°C, 21°C, and 24°C were carried out, and the harvested cut flowers were compared with those of a non-cooled control group. For flowers harvested in November, those from plants subjected to the night-cooling treatments had harder stems compared with those of the non-cooled control. In the next experiment, to determine the best timing and duration of the night cooling treatment, we applied three treatments to rooted cuttings planted on June 18, 2013; overnight cooling from sunset to sunrise, cooling for 4 h from sunset (End of Day cooling: EOD-cooling), and cooling for 4 h before sunrise (End of Night cooling: EON-cooling), and compared them with a non-cooled control. For flowers harvested in December, the node order of flowering was the same in the EOD-cooling treatment and the overnight cooling treatment, and was lower than those in the EON-cooling treatment and the non-cooled control. The number of days to flowering was shorter in the EOD-cooling treatment than in the non-cooled control. In October and November in the harvest season when the high temperature influenced the early growth stage, the stem quality of cut flowers was improved by night-cooling treatments, as indicated by a significantly smaller stem weeping angle than that in the non-cooled control group. These results suggested that an EOD-cooling treatment at 21°C for 4 h from sunset was as effective as an overnight cooling treatment to improve the quality of cut flowers by promoting stem hardness and flowering. This method is a cost-effective and efficient thermal management strategy to produce high-quality carnation cut flowers in hot conditions.
Okra pods, commonly eaten at an immature stage, undergo quick postharvest deterioration due to high respiration, water loss, wilting, toughening and decay. As okra is a tropical crop, its pods are susceptible to chilling injury (CI) at low storage temperatures. The effects of low temperature storage on the physio-biochemical properties of okra pods were determined. Chilling injury symptoms were found only in pods stored at 4°C and were more apparent after transfer to 25°C. In seeds, the CI index was positively correlated with seed browning, H2O2, malondialdehyde (MDA) content, and catalase (CAT) activity. Chilling-injured seeds had lower total phenolic content (TPC), antioxidant activity (DPPH scavenging activity and FRAP assay), peroxidase (POD), and superoxide dismutase (SOD) activities than non-injured seeds. Additionally, the seed browning index was related to high polyphenol oxidase (PPO) activity. In the pericarp, the CI index was also positively correlated with the H2O2 and MDA contents. The POD and SOD activities in chilling-injured pericarp were significantly lower than in non-injured pericarp. Chilling injury resulted in an initial increase in DPPH scavenging and CAT activities which later decreased as CI became severe. These results indicate that CI in okra is due to accumulation of H2O2, and MDA, as well as its weak antioxidant defense mechanism. This resulted in development of CI symptoms, including seed browning.