Shoot Harvest Research Articles

Pinching Impacts Cut Poinsettia Stem Quality and Profit Potential

The development of the Renaissance series of cut poinsettias, Euphorbia pulcherrima, presents unique opportunities and challenges to cut flower producers. This series has curled bracts, long stem length, excellent vase life, and is highly marketable. Literature indicates that this crop is suited for pot or bed production, but does not compare how cultural methods impact stem quality. This study assessed the impact of pinching on final stem quality and crop profitability. Uniform rooted cuttings of `Renaissance Red' obtained from a commercial supplier were transplanted into a 1.2 × 2.4 m bed containing a soilless media to obtain two plants per 0.09 m2. A total of 56 cuttings were used and grown using standard production techniques. Transplanting occurred on 29 July 2004 with half of the plants being pinched on 19 Aug. 2004. To minimize border effects, plants in the outside rows were discarded. Upon harvest, stem length, stem diameter, bract diameter, floral development, and number of axillary shoots were determined for 30 interior plants. Both pinched and unpinched plants produced marketable stems; however, unpinched plants produced longer thicker stems with larger bracts. The number of stems obtained per square foot was greater with the pinched plants. While overall quality was reduced, this increase in stem number offset potential lost profit. The production of quality cut stems of `Renaissance Red' poinsettias is possible with either pinched or unpinched plants.

Nutrient Removal Through Autumn Harvest of Phragmites australis and Thypha latifolia Shoots in Relation to Nutrient Loading in a Wetland System Used for Polishing Sewage Treatment Plant Effluent

The efficacy and feasibility of annual harvesting of Phragmites australis and Typha latifolia shoots in autumn for nutrient removal was evaluated in a wetland system used for polishing sewage treatment plant (STP) effluent. Aboveground biomass and nutrient dynamics nutrient removal through harvest were studied in parallel ditches with stands of Phragmites or Typhathat were mown in October during two successive years. The inflow rate of STP effluent to the ditches was experimentally varied, resulting in pairs of ditches with mean hydraulic retention times (HRT) of 0.3, 0.8, 2.3, and 9.3 days, corresponding to N and P mass loading rates of 122–4190 g N m− 2 yr− 1 and 28.3–994 g P m− 2 yr−1. Nitrogen and P removal efficiency by harvest of Phragmites and Typha shoots in October increased with increasing HRT, despite the opposite HRT effect on N and P standing stocks. This removal through harvest appeared to be useful in treatment wetlands with N and P mass loading rates lower than approximately 120 g N m−2 yr−1 and 30 g P m−2 yr−1, corresponding to a HRT of roughly 9 days in the ditches of this wetland system. At the HRT of 9.3 days, the annual mass input to the ditches was reduced through the harvest by 7.0–11% and 4.5–9.2% for N and P, respectively. At the higher nutrient mass loading rates, the nutrient removal through harvest was insignificant compared to the mass inputs. The vitality of Phragmites and Typha, measured as maximum aboveground biomass, was not affected by the annual cutting of the shoots in autumn over two years. The Typha stands yielded higher N and P removal efficiencies through shoot harvest than the Phragmites stands, which was largely the result of lower decreases in N and P standing stocks between August and October. This difference in nutrient standing stocks between the two species was caused by a combined effect of greater decreases in nutrient concentrations largely due to higher nutrient retranslocation efficiencies of Phragmitesplants and greater reductions in shoot Phragmites biomass because of leaf fall and mass resorption. Nutrient removal by harvesting Phragmites shoots can probably be doubled without a reduction in vitality of the stands by advancing the harvest date to mid-September, which would at least approach the nutrient removal by harvesting Typha shoots in October. Phragmites also may be more profitable in very low-loaded wetland systems because the vigor of Typha stands seemed to be more sensitive to a lower nutrient availability at N and P mass input rates lower than the range indicated.

Postharvest Changes in Activities of GS, ACC Synthase, ACC Oxidase, and PAL in Bamboo Shoots at Different Storage Temperatures

In this study, we investigated the postharvest changes in glutamine synthetase (GS; EC 6. 3. 1. 2), 1-aminocyclopropane-1-carboxylate (ACC) synthase (EC 4. 4. 1. 14), ACC oxidase (EC 1. 4. 3) and phenylalanine ammonia lyase (PAL; EC 4. 3. 1. 5) activities in relation to ammonia content, ethylene production, respiration rate, and texture and color changes after harvest of moso bamboo (Phyllostachys edulis) shoots stored at 1 and 20°C for up to 9 days. GS activity decreased in shoots stored at 20°C with increasing ammonia content up to approximately 6-fold the initial content after a 9-day storage period. Although the highest ACC oxidase activity corresponded to the highest ethylene production, the highest ACC synthase activity was delayed 8 h or more compared with that in the previous study. The development of PAL activity coincided with an increase in breaking strain at 20°C up to 3 days. Low-temperature storage of shoots at 1°C retained good shoot color and quality since it was effective in decreasing respiration rate, ammonia accumulation, ACC synthase, ACC oxidase, and PAL activities after the harvest of moso bamboo shoots.

Harvest management in rose-scented geranium (pelargonium sp.) for higher essential oil yield and superior quality under semi-arid tropics

Rose-scented geranium (Pelargonium species) is grown as a perennial crop for production of high value essential oil, which finds application particularly in high-grade perfumery, cosmetic products and aromatherapy. A field investigation was carried out during 2001-02 to study the harvest of shoots of the crop on attainment of 4, 6 or 8 fully expanded leaves (FEL) and its effect on essential oil yield and quality under semi-arid tropics. Harvesting of shoots with 4 FEL produced 6 harvests / annum against 4 and 3 harvests per annum in the treatments representing harvest of shoots with 6 and 8 FEL, respectively. Highest biomass yield (18.1 t ha−1 annum−1) among the treatments was, however, observed in the treatment 8 FEL. On the contrary, essential oil content in the biomass of treatment of 4 FEL was 27.3 and 55.5% higher than 6 FEL and 8 FEL treatments, respectively. Similarly, estimated essential oil yield in the treatment of 4 FEL was 17.4 and 30.7% higher than 6 FEL and 8 FEL treatments, respectively. Furthermore, the essential oil produced in the 4 FEL treatment was found to contain higher citronellol, geraniol, citronellyl formate, cis- and trans-rose oxides and 10 epi-γ-eudesmol and lower linalool, menthone and isomenthone, than other harvest treatments. The gross and net returns were also remarkably higher in the 4 FEL treatment beside benefit-cost ratio. It is suggested that rose-scented geranium can be harvested more frequently (six harvests per annum) on attainment of shoots with 4 fully expanded leaves in order to produce higher essential oil yield with superior quality and higher return.

Controle químico de parreira-brava (Cissampelos glaberrima) na cultura da cana-de-açúcar

A parreira-brava (Cissampelos glaberrima) e a erva-palha (Blainvillea romboidea) estão no início de sua dispersão na cultura da cana-de-açúcar no Estado de São Paulo e são espécies de extrema agressividade e de difícil controle. Objetivou-se neste trabalho estudar a eficácia dos herbicidas trifloxysulfuron-sodium + ametryne, picloram + 2,4-D, 2,4-D e fluroxypyr, aplicados em pós-emergência, no controle de parreira-brava e ervapalha em canaviais. O delineamento experimental utilizado foi o de blocos casualizados, com seis tratamentos e quatro repetições. Foram feitas avaliações visuais das porcentagens de controle, aos 7, 14, 21, 29, 36, 42, 56 e 90 dias após a aplicação (DAA) dos herbicidas. Medidas das alturas das plantas de cana-de-açúcar foram feitas aos 29 e 56 DAA, e a contagem do número de afilhos foi feita aos 33 DAA. Na colheita, fez-se a contagem do número de colmos, e a produção foi calculada através da pesagem dos colmos da parcela. Diante dos resultados obtidos, pode-se concluir que o trifloxysulfuron-sodium + ametryne (1.500 g ha-1) agiu rápida e eficientemente na parte aérea das plantas adultas de parreirabrava, porém não impediu que as brotações surgissem após os 42 dias da aplicação. No entanto, o picloram + 2,4-D (a 2.040 g ha-1) e o fluroxypyr (345 g ha-1) mantiveram níveis de controle da parreira-brava superiores a 90%, até 90 DAA. O controle de erva-palha mostrouse não-satisfatório com a aplicação de trifloxysulfuron-sodium + ametryne e bastante eficaz (100%) com os demais herbicidas.

POTENTIAL FOR GREENHOUSE AEROPONIC CULTIVATION OF URTICA DIOICA

Resent studies investigating aeroponic cultivation of medicinal plants have provided encouraging results for increasing yields, shortening time to maturity, and improving consistency and overall quality of produce over field production. The goal of the current study was to determine the applicability of aeroponic technology for the cultivation of the traditionally field grown herbaceous medicinal plant Urtica dioica. In addition, we investigated if control of nutrient delivery and repeated harvesting practices could be utilized to increase and direct yield of desired plant parts. Comparison of root and shoot dry weights between treatments revealed; (1) U. dioica cultivated in soil-less medium yielded equal shoot biomass and greater root biomass than aeroponically cultivated plants, (2) potassium and phosphorus ratios within the nutrient solution had no significant impact on yield or biomass allocation, and (3) multiple harvesting of aeroponic roots and shoots yielded greater total biomass of both roots and shoots than a multi-crop replanting strategy. Results suggest aeroponic technology could be a powerful tool for the cultivation U. dioica as well as a variety of other important herbaceous medicinal plants. However, further optimization of the plant growing environment is required to maximize and direct growth.

Cadmium accumulation in Allium schoenoprasum L. grown in an aqueous medium

The ability of Allium s choenoprasum L. (chives) to accumulate and tolerate cadmium in aqueous Hoagland medium at 50 μM and 250 μM was tested under continuous growth or several successive harvests of shoots. After 28 days of continuous growth, chives accumulated the metal up to 0.2% and 0.5% of its dry weight, when grown in 50 μM and 250 μM, respectively. In experiments that the leaves were successively harvested every 16 days, there were no obvious stress symptoms after six harvests during a period of 96 days at 50 μM Cd. At 250 μM, after 64 days and four harvests, inhibition of growth occurred. In each treatment, a total of 1.2 g kg −1 DW and 2.4 g kg −1 DW was accumulated in the leaves, respectively. Total SH compounds concentration in leaf was found significantly higher by 3 and 7.4 times in plants treated with Cd at 50 μM and 250 μM in comparison to the control, respectively, while no difference in the concentration of glutathione (GSH + GSSG) was found. Thus, it is assumed that sulphur-containing compounds, yet unknown, are involved in defensive mechanisms against heavy metals in chives. The results presented, point to chives phytoremediation potential, but also on the potential risk in accumulation of heavy metals in a commonly edible plant.

Organic carbon and plant nutrient dynamics under three land uses in the highlands of West Cameroon

Assessing land use-induced changes in soil systems is essential for addressing the problem of agroecosystem transformation and sustained land productivity. We compared organic carbon (OC) characteristics and plant nutrient levels in surface horizons (0–10 cm) of semi-permanent, mixed food crop fields (CF), Eucalyptus grandis plantations (EP) and tea (Camellia sinensis) plantations (TP) from an andic Palehumult in the highlands of West Cameroon. For more insight in organic matter transformations, OC, total nitrogen (TN) and NaHCO3 extractable phosphorus (NaHCO3–P) were analyzed on whole soils and size fractions (SF). Structural composition of soil organic matter (SOM) was assessed by solution 13C NMR spectroscopy. Land use conversion from CF to EP and ET increased OC stocks in surface horizons by a factor of 2.14 and 1.95 for EP and TP respectively after 15 years. In all land uses, O-alkyl C, aromatic C and carboxylic C were the dominant OC species, accounting for between 75.6 and 76.1% of total soil OC. The organic NaHCO3–P fraction was significantly higher (79.4±7.2 μg g−1) under TP and lowest under EP (58.8±4.3 μg g−1) as a result of phosphorus fertilization. The EP system recycled and accumulated substantial amounts of Ca and Mg in surface soil horizons. The inorganic NaHCO3–P fraction and K were significantly lower (P<0.05) under EP suggesting an immobilization in litter and standing biomass. TP had the lowest Mg level due probably to export through shoot harvest. Sites under EP and TP have significantly (P<0.001) higher proportion of silt and correlatively a lower proportion of clay. Soil size fractions exhibited distinct properties with respect to organic nutrient concentration, mineralization status and stability with silt and clay-sized fractions being enriched in OC and TN compared to whole soils. The highest quantitative changes after 15 years was recorded in the silt-sized fraction which accounted for 58–66% of total soil carbon.

The Influence of Location of Main Stem Segment Origin on Forcing and Rooting of Softwood Shoots of Betula nigra L.

The objective of this study was to investigate the effects of the position on the main stem that large stem segments were harvested from on forcing and subsequent rooting of Betula nigra L. (river birch) softwood shoots. The main trunks of eight adult-phase native trees (four trees per run of the experiment) were cut into 50-cm long segments from the ground up. The segments placed in horizontally in 52 × 25 × 6.5 cm (l × w × h) flats containing perlite and were positioned so the bottom one-third of the stem was within the medium. Shoots were forced under natural photoperiod and intermittent mist. This experiment was conducted twice. Data were collected weekly for fourteen weeks on the number of softwood shoots each segment produced, shoot length, number of rootable shoots (&gt;6 cm long), the length of time that the stem segments produced rootable shoots, and the rootability of these shoots treated with 3000 ppm IBA in talc. The number of harvested shoots was greater in Run 1, with the basal segments producing the most harvestable shoots. However, the upper segments in Run 2 produced the most harvestable shoots. Softwood shoots that rooted were placed under intermittent mist. Out of the 540 harvested shoots for both runs, 82.4% rooted, with the majority of those from Run 1. Shoots harvested from this run began producing roots about 6 weeks after harvest, and continued until the end of the experiment. Run 2 shoots began root initiation about 3 weeks after harvest and ended about 2 weeks before the end of the experiment. Run 1 had an mean of 8.3 roots per shoot and Run 2 had an mean of 6.2 roots. The relationship between juvenility and shoot forcing and subsequent rooting will be discussed.

Micropropagation of Sesbania rostrata from the Cotyledonary Node

Multiple shoots were induced from the cotyledonary nodes derived from seedling of Sesbania rostrata on Nitsch (1969; N) medium supplemented with various concentrations of benzyladenine (BA). 1 mg dm−3 BA proved to be the best, eliciting 5.8 ± 1.0 shoots per explant in 100 % cultures. The elongation of shoots was best at 2.0 mg dm−3 BA. The shoot proliferation capacity increased to 7.5 shoots per explant following transfer of explants to the fresh shoot multiplication medium (MS + 1.0 mg dm−3 BA), after an initial incubation of 30 d. To further enhance number of shoots per explant an alternative strategy of cultivation of mother explant on fresh shoot multiplication medium after excision of shoots was adopted. Following the repeated harvesting of shoots an average of 33 shoots per explant could be obtained. The in vitro regenerated shoots produced roots when transferred to half-strength MS medium supplemented with 3 % sucrose and 1 mg dm−3 IBA. The developed plantlets were planted in the soil and transferred to the field after an acclimatization period of 3 – 4 months. These plants produced flowers and fruits in the field and exhibited the development of prominent and more organized stem nodules as compared to the in vivo raised plants of the same age.

Shoot regrowth and age-specific rhizome storage dynamics of Phragmites australis subjected to summer harvesting

Shoots of a monospecific wetland stand of Phragmites australis (Cav.) Trin. ex Steud. in Central Japan were harvested during two summer months in June (June-cut stand) and July (July-cut stand) and their effects on the stand morphology, above- and below-ground biomass and rhizome storage level (in terms of age-specific rhizome bulk density, ρ rhiz), were investigated between themselves and to an uncut control stand. Both harvesting treatments increased leaf production and decreased shoot height, stem diameter, and the storage accumulation capacity of older rhizome age categories, the June-cut stand showing the lowest ρ rhiz. Even though the year-end age-specific rhizome reserve level did not reach to that of uncut stand values, both treatments accelerated the post-harvest rhizome reserve accumulation rates (i.e. rate of ρ rhiz increment) stimulated by shoot harvesting, especially in younger rhizomes and were negatively and linearly correlated with rhizome age. The study identified the seasonal changes of the rhizome reserve quality as essential for proper vegetation management. July or August is the appropriate harvesting time for plant stands used in phytoremediation and wastewater treatment, where a larger shoot-bound nutrient stock is removed, while preserving a healthy stand for the subsequent years. A harvest in May to June would be more effective in reducing the growth, and repeated June-cutting may likely weaken the stand beyond repair after several years.

Nitrate and potassium uptake by greenhouse roses ( Rosa hybrida) along successive flower-cut cycles: a model and its calibration

Rose ( Rosa hybrida L.) plants grown for cut-flower production in greenhouses produce flowers in flushes year-round. Crop models for this system must handle the cyclical nature of productivity, which is determined by the horticultural production methods. Nutrition was not accounted for in previous rose growth models, since little is known about uptake of the essential nutrients by rose roots. The aim of the current study was to measure uptake rates of nitrogen and potassium by roses, to be included in a production model. Rose plants var. ‘Kardinal’ were grown in the greenhouse in aero-hydroponics nutrient solution with 3 mM nitrate (NO 3)-N and 1 mM potassium (K). After several flower growth/harvest cycles, the plants were transferred to a growth chamber in groups of three, every 10 days. The growth chamber provided 25 °C and 16 h day length. The nutrient solutions were sampled periodically while maintaining the volume constant at 5 l, and analyzed for NO 3 and K concentrations reduction. The roots were harvested at the end of each depletion series, and their lengths measured. Influx of NO 3 and K into roots was obtained by fitting a Michaelis–Menten function to the concentration depletion data. There was a cyclic rhythm of both the nutrients’ influx rates over time, with a decline in uptake after shoot harvest, and an increase during flower development, with maximal values towards flower opening. The results were incorporated in a simulation model for nutrient uptake by roses along successive flower-cutting cycles. This simulation assumes a constant number of identical flowering branches, which would be cut sequentially at flower maturity, and result in new shoot growth, assumed to follow a logistic function of time. Uptake rates of NO 3 and K were assumed to follow the changes in leaf area and shoot nutrient percentage, to compensate for N and K demand by the shoot; the root system dimensions and its effective aging are assumed constant. Simulated N and K uptake agreed with published data of their accumulation and percentage in growing rose branches along a flower-cut cycle.

Micropropagation of camphor tree ( Cinnamomum camphora )

Multiple shoots were induced from shoot tips and nodal segments of a 12-year-old tree of Cinnamomum camphora on Woody Plant Medium (WPM) supplemented with BA and kinetin. The nodal segments from the in vitro developed plantlets could be induced again to produce a large number of harvestable shoots. Harvested shoots were rooted in vitro in WPM supplemented with activated charcoal (AC) and IBA. The plantlets were transferred to thermocol cups after which they were replanted into polybags and then to field. These plants survived with over 90% success under field conditions and exhibited vigorous growth. This system could be utilized for large-scale multiplication of C. camphora by tissue culture.

Fate of 15N-nitrate in unplanted, planted and harvested riparian wetland soil microcosms

Riparian wetlands are important for the protection of river water quality in agricultural landscapes by intercepting and removing nutrients, such as nitrate (NO 3 −), in runoff. However, limited information is available on the relative importance of biological NO 3 − removal processes in these ecosystems. In this study the fate of 15N-NO 3 − was investigated for 32 days in three types of wetland soil microcosm (unplanted, planted, and planted with shoot harvest) in order to identify the key processes responsible for NO 3 − removal, elucidate the role of the wetland plant and determine the effect of shoot harvest. 15N-NO 3 − solution (7.9 mg N l −1, 99 at.% 15N) was added to each microcosm at a rate of 0.5 μg N g −1 soil every 2 days. In both types of plant-inhabited microcosm, similar proportions of added 15N-NO 3 − were denitrified (61–63%), soil-immobilised (24–26%), plant-assimilated (11–15%) and reduced to ammonium (NH 4 +) (<1%). However, in unplanted microcosms, 49% was reduced to NH 4 +, 29% denitrified and 22% immobilised. Elevated denitrification in the presence of the plant, glaucous sweetgrass ( Glyceria declinata), was attributed to a higher degree of soil oxidation, which is considered to be the principal regulator of NO 3 − partitioning between denitrification and DNRA. Shoot harvest did not affect the fate of 15N-NO 3 −, but it decreased new shoot production (by a factor of 3.9), inhibited new root production, and increased the NO 3 − assimilation capacity of shoots (by a factor of 5.2). Although this study lasted for only 1 month, the results have important implications for riparian ecosystem management, restoration and design. The water quality protection afforded by riparian wetlands might be substantially enhanced by maximising vegetation cover with plants like G. declinata that promote high denitrification nitrogen (N) losses. In contrast, shoot harvest as a mechanism of permanent N loss may be much less important.

Growth, morphology, and cold hardiness of Chamaecyparis nootkatensis seedlings originating from an abbreviated reproductive cycle

A common garden study investigated growth, morphology, and cold hardiness of yellow-cedar (Chamaecyparis nootkatensis (D. Don) Spach) seedlings originating from seed that had matured at an accelerated rate. This early maturing seed, produced at a low-elevation southern Vancouver Island seed orchard, was known to have similar germinability and seedling morphology as high-elevation normally maturing seeds. Population differences in 3-year-old seedlings were evident only in shoot harvest index (ratio of stem/shoot dry weight). The amount of stem elongation that occurred prior to the formation of secondary foliage (juvenile height) and harvest index were weakly correlated with source elevation at which maternal parents were developed. Traits that exhibited no discernable differences between progeny from early maturing seed and the control normally maturing seed included midwinter cold hardiness testing and selected measures of shoot morphology and growth. The control seedlings had significantly less height growth prior to the transition of primary foliage to secondary foliage formation than did the seedlings originating from early maturing seed.

Response of soil food-web structure to defoliation of different plant species combinations in an experimental grassland community

We established a greenhouse experiment based on replicated mini-ecosystems to evaluate the effects of defoliation of different plant species combinations on soil food-web structure in grasslands. Plant communities, composed of white clover ( Trifolium repens), perennial ryegrass ( Lolium perenne) and plantain ( Plantago lanceolata), were subjected to the following defoliation treatments: no defoliation of any species (control) and selective trimming of all possible one-, two- and three-way combinations of the species either to 27 cm height (weak defoliation) or to 15 cm height (strong defoliation) above the soil surface three times over a 10-week period. Successive defoliations removed the largest amounts of shoot mass from systems in which T. repens was included among the defoliated species because T. repens dominated aboveground plant biomass. At the final harvest shoot mass was lowest in treatments that included defoliation of T. repens, while total root mass was on average lower in strongly than in weakly defoliated systems and did not differ between the control and defoliation treatments. Total shoot production was not affected by defoliation. Microbial basal respiration and soil NO 3-N concentration differed between the combinations of defoliated species; e.g. microbial respiration was on average 32% lower in systems in which only L. perenne was defoliated than in systems in which only T. repens was defoliated. Microbial biomass and soil NH 4–N concentration were not significantly affected by defoliation treatments. Enchytraeid abundance differed significantly between the combinations of defoliated species: in systems in which only L. perenne was defoliated enchytraeid abundance was on average 88% lower than in systems in which all species or only T. repens were defoliated. Enchytraeid abundance was also positively associated with total defoliated shoot mass. Abundances of both bacterial-feeding and fungal-feeding nematodes were affected by the combination of defoliated species; e.g. the abundance of bacterial feeders was on average 52% lower in systems in which only T. repens was defoliated than in systems in which both P. lanceolata and T. repens were defoliated. Fungal-feeding nematodes were also more numerous in strongly than in weakly defoliated systems and positively associated with total defoliated shoot mass. Herbivorous nematode abundance was not significantly affected by defoliation treatments. The results show that the response of soil food webs to defoliation can be affected by which combination of species in a plant community is defoliated. Further, it seems that the role of the combination of species that are defoliated may for some components of the soil biota (e.g. fungal-feeding nematodes) be explicable simply in terms of the total mass of foliage removed. However, for other components of the soil biota (e.g. bacterial-feeding nematodes and enchytraeids) species-specific properties of different plant species in the combination of defoliated species are also clearly important, over and above simple mass removal effects of defoliation.

Interaction between Explant Size and Cultivar Affects Shoot Organogenic Competence of Watermelon Cotyledons

Organic competence of different explant sizes and locations on watermelon seedlings was determined by calculating the percentage of cotyledon explants that produced adventitious shoots. About 52% (214/412) of explants prepared from the proximal region of cotyledons formed shoots, whereas only ≈6% (24/411) of distal explants did so. Shoot formation was limited to the proximal end of basal explants but was not restricted to any specific region on distal ones. The percentage of explants that produced harvestable shoots was greater from basal halves than basal quarters in `Sweet Gem', `Crimson Sweet', and `Minilee', but explant size did not affect adventitious shoot regeneration of `Yellow Doll', resulting in significant interaction between cultivar and explant size. This study indicates that cultivars that respond poorly to in vitro procedures may have fewer cells competent for shoot regeneration, requiring special care during explant preparation.

Recurrent production of plants of black plum, Syzygium cuminii (L.) Skeels, a myrtaceous fruit tree, from in vitro cultured seedling explants.

The epicotyl segments bearing scaly leave(s), excised from in vitro grown seedlings of Syzygium cuminii, produced multiple shoots when cultivated on Murashige and Skoog's (MS, 1962) medium supplemented with different concentrations of BA (0-2 mg l-1). The optimum response was recorded on the medium containing 1 mg l-1 BA. An average of 8.6 shoots per explant were produced 60 days after inoculation, following transfer to fresh medium after 30 days. The shoots were excised, and the residual explants were transferred to fresh medium, where they again developed shoots. Up to five such passages resulted in the production of shoots from the repeatedly subcultured original explants. However, during the fifth passage, organogenic response was negligible and the explants turned brown thereafter. Following repeated harvesting of shoots and subculture of the residual explants, an average of 29 shoots per explant was obtained. The in vitro developed shoots produced roots when transferred to Knop's medium supplemented with 2% sucrose and 1 mg l-1 IAA. The developed plantlets were planted in soil and transferred to fields after an acclimatization period of 7-8 months. These plants have been thriving well for more than 3 years. The nodal explants excised from in vitro developed shoots and plants also exhibited a similar response when cultured on MS+1 mg l-1 BA. Thus, a protocol has been developed to raise plants of S. cuminii at any time of the year.

Varying the ratio of 15 N-labelled ammonium and nitrate-N supplied to creeping bent: effects on nitrogen absorption and assimilation, and plant growth.

The relative rates of ammonium and nitrate-N uptake and assimilation by creeping bent (Agrostis stolonifera), were investigated for plants grown in soil and supplied with three different ratios of ammonium and nitrate-N. Following two preliminary defoliations, plants were supplied with the equivalent of 150 kg N ha-1 , given as 15 N-(differentially) labelled NH4 + and NO3 - -N in three different ratios (20:80, 50:50 and 80:20), followed by sequential destructive harvests of shoots and roots at four points during a 35-d regrowth period. Maximum use of labelled nitrogen and 'exhaustion' of soil mineral nitrogen reserves occurred much earlier when plants were supplied with half or more of their nitrogen as ammonium, than occurred when they were supplied predominately with nitrate-N. The lack of consistency in the patterns of ammonium and nitrate-N absorption, however, implied that the plants had no specific preference for either nitrogen form. Supplying plants with different combinations of ammonium and nitrate produced distinctive differences in plant morphology. In the high nitrate treatment, plants preferentially partitioned resources into shoot and stolon formation, whereas in the high ammonium treatment, resources were preferentially partitioned into root production. These changes in plant morphology might be adaptations to aid species survival in environments associated with a predominance of either nitrogen form.

Transfer from Long to Short Photoperiods Affects Production Efficiency of Day-neutral Rice

The day-neutral, semidwarf rice (Oryza sativa L.) cultivar Ai-Nan-Tsao was grown in a greenhouse under summer conditions using high-pressure sodium lamps to extend the natural photoperiod. After allowing 2 weeks for germination, stand establishment, and thinning to a consistent planting density of 212 plants/m2, stands were maintained under continuous lighting for 35 or 49 days before shifting to 8- or 12-h photoperiods until harvest 76 days after planting. Non-shifted control treatments consisting of 8-, 12-, or 24-h photoperiods also were maintained throughout production. Tiller number increased as duration of exposure to continuous light increased before shifting to shorter photoperiods. However, shoot harvest index and yield efficiency rate were lower for all plants receiving continuous light than for those under the 8- or 12-h photoperiods. Stands receiving 12-h photoperiods throughout production had the highest grain yield per plant and equaled the 8-h-photoperiod control plants for the lowest tiller number per plant. As long as stands were exposed to continuous light, tiller formation continued. Shifting to shorter photoperiods late in the cropping cycle resulted in newly formed tillers that were either sterile or unable to mature grain before harvest. Late-forming tillers also suppressed yield of grain in early-forming tillers, presumably by competing for photosynthate or for remobilized assimilate during senescence. Stands receiving 12-h photoperiods throughout production not only produced the highest grain yield at harvest but had the highest shoot harvest index, which is important for resource-recovery strategies in advanced life-support systems proposed for space.