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- Author or Editor: Yao-Chien Alex Chang x
Pseudobulbs are carbohydrate storage organs in Oncidesa. A current pseudobulb forms on a developing vegetative shoot in each growth cycle and it becomes a back pseudobulb when the next vegetative shoot emerges. Both current and back pseudobulbs store carbohydrates, but their functions might differ because the inflorescence emerges from the new (current) shoot after the shoot has developed to a certain stage. This study investigated carbohydrate storage and use in current and back pseudobulbs. We analyzed carbohydrates in the current pseudobulb at five stages during inflorescence development. Glucose and fructose were the highest in the current pseudobulb in the first two stages, when the inflorescence was 10 to 35 cm tall. Then, both glucose and fructose decreased in the following stages to support inflorescence development, but starch increased at that time. In addition, we used Oncidesa with one or two new vegetative shoots to study the use of carbohydrates in pseudobulbs during growth cycles. In both plants with one or two shoots, glucose and fructose accumulated when current pseudobulbs formed, but plants with two new shoots had smaller current pseudobulbs and lower monosaccharide concentrations. Plants with two shoots also consumed more starch in all back pseudobulbs, whereas in the plants with one new shoot, starch only decreased significantly in the first back pseudobulb, which was closer to the new shoot. In addition, if an inflorescence did not develop in the previous growth cycle, new shoots used the monosaccharides that remained in the youngest back pseudobulb for growth; at the same time, starch accumulated in all back pseudobulbs. The current pseudobulb was the actively growing part. Its main carbohydrates were monosaccharides, which accounted for 25% of dry weight and Oncidesa used these carbohydrates mainly for inflorescence growth. After monosaccharides in the pseudobulb were used, the pseudobulb began to store starch. Back pseudobulbs, in which >50% of dry weight was starch, were the primary storage organs that supported new vegetative shoot growth and partly supported later inflorescence development that emerged from the new (current) shoot.
Plants of Phalaenopsis orchid are known for their great resilience and ability to flower under less than ideal conditions, including long periods without fertilization. Significant nutrient storage is thought to account for this characteristic; however, the use of stored nutrients in Phalaenopsis has not been fully studied. We used 15N-labeled Johnson’s solution to trace the use of stored nitrogen (N) and recently absorbed fertilizer N in Phalaenopsis given various fertilizer levels during forcing. By separately labeling fertilizer N applied to Phalaenopsis Sogo Yukidian ‘V3’ plants 6 weeks before and 6 weeks into forcing, we found in the inflorescence that the ratio of N derived from fertilizer applied 6 weeks before forcing to the N derived from fertilizer applied 6 weeks into forcing was 43% to 57%. With 90% reduction in fertilizer concentration during the reproductive stage, the ratio increased to 89% to 11%, indicating that stored N becomes a significant N source for inflorescence development when fertility becomes limited. Reducing fertilizer level during the reproductive stage from full-strength Johnson’s solution down to zero decreased the dry weight of newly grown leaves, reduced the number of flowers from 10.8 to 8.9, and slightly increased the time required between initiation of forcing and anthesis. However, the overall effect of reduced fertilization on the growth and flowering of Phalaenopsis Sogo Yukidian ‘V3’ plants in this study was slight, because under little or no fertilization, more stored N was mobilized and this was sufficient to meet most of the N demand for inflorescence development.
In the commercial production of phalaenopsis orchids, the cultivation time after deflasking is used to describe the plant age and maturity. Carbon-to-nitrogen (C/N) ratio is often used as an indicator of plant growth and flowering potential. High C/N ratios are considered to promote reproductive growth, and low C/N ratios are associated with the early vegetative growth or even inhibiting flowering. This study investigated how plant age and maturity affected flowering ability and flower quality of phalaenopsis and their relationship to C/N ratio. The plant materials of various ages were the purple, small-flowered Phalaenopsis Sogo Lotte ‘F2510’ and white, large-flowered P. Sogo Yukidian ‘V3’, which were 2 to 7 months and 10 to 20 months after deflasking, respectively. Plants were placed under 25/20 °C for 4 months to force flowering and investigate the flowering-related parameters. The leaf C/N ratio of both varieties increased in general with the increase of plant age. The spiking (flower-stalk emergence) rate of P. Sogo Lotte ‘F2510’ 2 months after deflasking was only 42%, which indicates that these plants were not completely out of their juvenile phase, whereas that of those 3 to 7 months after deflasking was 100%, indicating that plants had acquired full flowering ability. No linear correlation was found between the C/N ratio and days to spiking, to first visible bud, to first flower open, and to 90% flower opening in the white, large-flowered P. Sogo Yukidian ‘V3’. However, there was a positive correlation between the C/N ratio and inflorescence length, flower-stalk diameter, first flower diameter, and flower count. Thus, the C/N ratio is feasible to be used as an indicator for assessing the flowering quality in phalaenopsis.
Phalaenopsis (Phalaenopsis spp.) is the most important indoor potted plant worldwide. Tissue analysis is very important for managing fertilization practices but the effects of sampling position and plant maturity must be considered. However, there has been little research on the distribution of tissue carbon (C) and nitrogen (N) among leaves and changes of tissue C and N composition during various developmental stages in phalaenopsis. In this study, we thus determined the effects of leaf age, plant maturity, and cultivars on C and N partitioning in phalaenopsis. Overall, C concentration was more uniform and was less affected by the abovementioned factors investigated, whereas N concentration significantly decreased as leaves aged or as plants matured. In P. Sogo Yukidian ‘V3’, new expanding leaf had the highest N concentration of 2.72% of dry weight (DW) and seventh mature leaf had the lowest value of 1.48% DW. Results also indicate that N was not evenly distributed within a leaf, whereas N concentration gradually decreased from the leaf tip to the leaf base. The middle section of the second mature leaf is an appropriate tissue for sampling to obtain the representative N and C concentrations in phalaenopsis. As for the changes in C and N composition through five developmental stages, two cultivars were compared, including the large, white-flowered P. Sogo Yukidian ‘V3’ and the small, purple-flowered P. Sogo Lotte ‘F2510’. As the large-flowered ‘V3’ grew from deflasked plantlet to fully matured plant (18 months after deflasking) in a 10.5-cm pot, whole-plant N concentration decreased from 4.63% DW to 1.67% DW and C/N thus increased from 9.1 to 26.1. Despite the large difference in plant size, the small-flowered ‘F2510’ had a similar trend and values during vegetative growth stages. However, the two cultivars had different trends during reproductive stages. Tissue N concentration and C/N did not further change as mature large-flowered ‘V3’ plants were forced to flower. By contrast, tissue N concentration in small-flowered ‘F2510’ further decreased and C/N thus further increased, which was due to its small stored N pool. Major N sink organ shifted from roots to inflorescences during reproductive growth and the stored N in roots as well as in leaves was then used for flower development.
The flowering control of Oncidesa Gower Ramsey ‘Honey Angel’ is important and in-demand by the industry. Therefore, an understanding of the development of inflorescence and vegetative shoot from the leaf axils on the current shoot is required. The internode of a young Oncidesa current shoot between the 0th (at the base of the pseudobulb) and 1st (immediately above the pseudobulb) nodes can enlarge to form a pseudobulb, and the axillary bud on the 0th or -1st (immediately below the 0th node) node can differentiate into an inflorescence bud. The axillary buds on the lower nodes (-2nd to -4th nodes) can remain vegetative. In this study, we investigated the growth and anatomical features of axillary buds at various stages during the growth of the current shoot. We sampled the axillary buds on the 0th to -4th nodes from the current shoots when they were 10, 15, 20, 25, and 30 cm in length for sectioning and anatomical observations. Vegetative buds on the -2nd to -4th nodes grew faster and had more nodes than the inflorescence bud when the current shoot grew from 10 to 25 cm. However, when the current shoot elongated from 25 to 30 cm, the length and node number in the inflorescence bud on the 0th node increased and the inflorescence branch primordia were observable. The length and node number of the inflorescence bud became the same as that of the vegetative buds, which had no further growth, whereas the current shoot grew from 25 to 30 cm. The pseudobulb began to emerge from the leaf sheath (unsheathing) when the current shoot had reached 30 cm in length. Therefore, the time when the pseudobulb started to unsheathe from its subtending leaf was critical for the reproductive growth of Oncidesa Gower Ramsey ‘Honey Angel’ when growth acceleration of the inflorescence bud occurred. Evaluating the current shoot length can be a nondestructive method of estimating the developmental stage of the inflorescence bud.
Growers realize the importance of nitrogen (N) on the vegetative growth of phalaenopsis orchids (hybrids of Phalaenopsis sp.), but often overlook its influence on reproductive growth. Low N may result in slow plant growth, pale-green leaves, abscission of lower leaves, and few flowers in phalaenopsis. Increasing N concentration up to 200 mg·L−1 promotes leaf growth and increases flower count. High N concentration promotes lateral branching on the flowering stalk, thereby greatly increasing the total flower count and elevating the commercial value. It is important that N be continually applied during the forcing period for best flowering performance, particularly for those that had undergone international shipping. For the vegetative phalaenopsis plants that are induced to flower without being shipped internationally, the N that is already in the plant before spiking provides 43% and the N being absorbed by roots after cooling provides 57% of the total N in the inflorescence at time of visible bud. When insufficiently fertilized or no fertilization is applied during the forcing period, more of the existing N in a plant is mobilized for inflorescence development. Phalaenopsis roots can take up all three forms of N [i.e., nitrate (NO3-N), ammonium (NH4-N), and urea] directly. In two studies, phalaenopsis plants were supplied with the same amount of total N but with varying NO3-N from 100%, 75%, 50%, 25%, to 0% (a common N concentration was achieved by the substitution of the respective balance with NH4-N). Plants were smaller when receiving 75% or 100% NH4-N with a tendency of decreasing top leaf width and whole-plant leaf spread as NO3-N decreased from 100% to 0%. Spiking was delayed and spiking rate decreased when plants were grown in sphagnum moss, but not a bark mix, and received more than 50% of the N in NH4-N. As the ratio between NO3-N and NH4-N increased, flowers became increasingly larger. The negative effects of low ratios of NO3-N to NH4-N were more severe in the second flowering cycle. When supplied with 50% or more NH4-N, the absorption of cations by phalaenopsis roots declined, with reduced concentrations of calcium and magnesium in plants, while symptoms of ammonium toxicity appeared, including growth retardation, chlorotic leaves, and necrotic roots. In conclusion, adequate N and its continual supply during both vegetative and reproductive stages are recommended for the best growth and flowering of phalaenopsis. Since phalaenopsis plants prefer N in the NO3-N form, it is suggested that growers choose and apply a fertilizer with nitrate as the major N source.
The vase life of Eustoma cut flowers can be extended by adding sugars to the vase solution, but the exact role of sugars and how they are translocated in tissues are not clear. Thus, we observed the preserving effect of different sugars in vase solutions on Eustoma and compared sugar concentrations in vase solutions and in the flowers as well as stems and leaves of cut flowers in a solution containing 200 mg·L−1 8-hydroxyquinoline sulfate (8-HQS) with and without 20 g·L−1 sucrose during different flowering stages. Inclusion of glucose, fructose, or sucrose in the vase solution extended the vase life of cut flowers with no significant differences among sugar types. During flower opening, the concentration of added sucrose in the vase solution dropped, and the fresh weight (FW), glucose concentration, and sucrose concentration of flowers in sucrose solutions increased, whereas flowers in solutions without sucrose had lower FW and glucose concentrations. During flower senescence, sugar concentration in the vase solution did not change much, but the FW and sucrose concentrations in all flowers declined, although the FW of sucrose-treated flowers fell more slowly. For stems and leaves in the sucrose solution, sugar concentrations increased during the first 7 days with only glucose slightly declining during senescence, whereas the FW was maintained during the entire vase life. In contrast, FWs of those in the solution without sucrose gradually declined. In conclusion, sucrose in the vase solution promoted flower opening and maintained the water balance of Eustoma cut flowers. Glucose and fructose also extended the vase life, likely in similar ways.
Cyrtopodium paranaense is a tropical terrestrial orchid, which propagates mainly through sexual seed germination. In this study, we document the asexual morphogenesis of the root tip to protocorm-like body (PLB) conversion in Cyrtopodium paranaense. Protocorm-like bodies sporadically developed from root tips of flask-grown seedlings in the absence of any exogenous plant growth regulators (PGRs). The compact PLBs ultimately gave rise to normal plantlets. Histological observations revealed that the root cap became dissociated from the root apex at an early stage followed by dispersed extension of root vascular strands into nascent PLBs. Protocorm-like bodies also developed from the root central stele tissue. In root tip segment cultures, PLBs were not formed without providing PGRs but were efficiently formed from root tips in Murashige and Skoog (MS) medium supplemented with 10.2 μM indole-3-acetic acid (IAA) and 9.0 μM thidiazuron (TDZ). Both IAA and TDZ promoted the formation of PLBs; however, TDZ did not induce PLB formation in the absence of IAA, indicating a synergistic effect of the two PGRs. Protocorm-like bodies were proliferated and subsequently plants regenerated in PGR-free MS medium. Root tip culture may be used as an alternative method for the propagation of Cyrtopodium paranaense.
The popularity of the nobile-type dendrobium (Dendrobium nobile hybrids) has been increasing globally. More information regarding the effects of long-distance shipping, from producing countries to destination market countries, on the post-shipping plant performance is needed. In this study, two nobile-type dendrobium cultivars were subjected to simulated dark shipping (SDS) at various temperatures and durations. Changes in net CO2 uptake rate (Pn), chlorophyll fluorescence, and leaf relative water content after plants had been treated with SDS were investigated. Furthermore, shipped plants were vernalized to investigate the effect of dark shipping on the subsequent flowering quality. Dark shipping for 7 days at 15 °C did not affect the post-shipping photosynthetic performance of D. Lan Tarn Beauty. Increasing the shipping duration from 7 to 21 days increased the time required for Pn recovery from 1 to 12 days. Dendrobium Lan Tarn Beauty recovered its Pn within 4 days when shipped for 21 days at 10 °C, and this was prolonged to 11 days when the plants were shipped at 20 °C. Changes in Fv/Fm indicated that there was no marked damage to either cultivars, and the leaf relative water content was little affected by SDS. Dendrobium Lan Tarn Beauty and D. Lucky Girl shipped at 10 °C flowered 5 and 8 days earlier, respectively, compared with unshipped plants. Regardless of the shipping conditions, shipped D. Lucky Girl had a lower flower diameter and higher total flower count than unshipped plants. No differences were found in the number of nodes with flowers or the total flower count between shipped and unshipped D. Lan Tarn Beauty. Our study suggested that dark shipping for up to 21 days is possible for nobile-type dendrobiums. We recommend shipping temperatures of 10 to 15 °C to reduce the detrimental effects caused by long-term dark shipping.
Sphagnum moss has been used as the major substrate for cultivating Phalaenopsis spp. in China, Japan, and Taiwan. With a lengthened duration of cultivation, the pH of the moss gradually declines. It is not understood what causes this decline in substrate pH. Using the vegetatively propagated Phal. Sogo Yukidian ‘V3’, this study investigated if substrate, fertilization, light, and plant roots could be the cause of pH decline in the substrate. The results showed that, although increasing fertilizer concentration resulted in a low initial pH (pH measured by the pour-through technique at first fertilization), fertilization itself was not the primary cause of the long-term pH decline. Regardless of whether the sphagnum moss was fertilized, the pH of the substrate without plants increased as time progressed, whereas the pH of the substrate in which living Phalaenopsis plants were growing declined with time. Although the magnitude and course of pH decline were different in various substrates, the pH of sphagnum moss, artificial textile fiber, and pine bark substrates in which living plants were growing declined with time. Whether the substrate was exposed to light (clear pots) or not (opaque pots) had no effect on substrate pH, indicating that algae were not a factor in pH decline. Therefore, the roots of Phalaenopsis may be the major contributor to substrate pH decline during production.