Controlled-environment Glasshouses Research Articles

Investigating how nitrogen nutrition and pruning impacts on CBD and THC concentration and plant biomass of Cannabis sativa

Precise crop fertilization requires an in-depth understanding of plant uptake and utilisation to optimise sustainable production. This study investigated the influence of nitrogen (N) nutrition and pruning on the cannabinoid concentrations and biomass of a commercial cannabis cultivar; the rationale for this study is how N supply and pruning affect cannabinoid yields and concentration in a commercial setting. Clones of a Cannabis sativa L. (CBD-type) were grown in a controlled-environment glasshouse in pots with coarse sand. After five weeks of vegetative growth under 210 mg/L N and an 18 h light regime, rates of 30, 60, 210, and 500 mg/L N were applied to plants for twelve weeks and a light regime set at 12 h. Double stem pruning was applied as an additional treatment to investigate efficacy on biomass increase. Biomass, N concentrations, and cannabinoid concentrations were measured after the final harvest. Pruning treatment did not increase cannabinoid concentrations or affect biomass. It was coincidentally found that plants on the glasshouse edge with higher exposure to sunlight developed more biomass and higher cannabinoid concentrations. Only biomass in leaves was increased significantly via higher nitrogen nutrition. Cannabinoid concentration, as well as cannabinoid yield per plant were decreased with the increase in N supply. High rates of fertilizer are not recommended because of reduced cannabinoid concentration and biomass yield: the ideal N supply is likely to be between 60 and 210 mg/L. This research will benefit growers and advisors in understanding the complexity of effects of nitrogen fertiliser and pruning practices on plant biomass and secondary metabolite production in medicinal cannabis.

Manipulation of the Phytochemical Profile of Tenderstem® Broccoli Florets by Short Duration, Pre-Harvest LED Lighting.

Light quality has been reported to influence the phytochemical profile of broccoli sprouts/microgreens; however, few studies have researched the influence on mature broccoli. This is the first study to investigate how exposing a mature glasshouse grown vegetable brassica, Tenderstem® broccoli, to different light wavelengths before harvest influences the phytochemical content. Sixty broccoli plants were grown in a controlled environment glasshouse under ambient light until axial meristems reached >1 cm diameter, whereupon a third were placed under either green/red/far-red LED, blue LED, or remained in the original compartment. Primary and secondary spears were harvested after one and three weeks, respectively. Plant morphology, glucosinolate, carotenoid, tocopherol, and total polyphenol content were determined for each sample. Exposure to green/red/far-red light increased the total polyphenol content by up to 13% and maintained a comparable total glucosinolate content to the control. Blue light increased three of the four indole glucosinolates studied. The effect of light treatments on carotenoid and tocopherol content was inconclusive due to inconsistencies between trials, indicating that they are more sensitive to other environmental factors. These results have shown that by carefully selecting the wavelength, the nutritional content of mature broccoli prior to harvest could be manipulated according to demand.

Petiole length reduction is an indicator of waterlogging stress for Trifolium subterraneum ssp. yanninicum

Background and aimsThe pasture legume Trifolium subterraneum ssp. yanninicum exhibits waterlogging tolerance. This study investigates diversity for waterlogging tolerance within ssp. yanninicum. We tested the hypotheses that (1) variation for waterlogging tolerance exists within ssp. yanninicum and (2) is related to phenotypic and growth trait differences, which (3) reflect eco-geographic variables at site of origin.MethodsTwenty-eight diverse ssp. yanninicum ecotypes collected from the Mediterranean region and four cultivars were grown in a controlled environment glasshouse. Seedling traits were measured at 14 and 21 days after sowing. Waterlogged and free-draining (control) treatments were then imposed for 28 days. Relative distance and multivariate plasticity indices were calculated.ResultsUnder waterlogging, shoot (87–108% of controls) and root (80–116% of controls) relative growth rates (RGRs) differed significantly among ssp. yanninicum. Waterlogging tolerance, as assessed by shoot RGR, had strong positive correlations with root RGR (r = 0.86; P < 0.001), petiole length (r = 0.59; P < 0.001) and leaf size (r = 0.55; P < 0.01) under waterlogging. The proportion of biomass as leaf increased under waterlogging, due to leaf size being maintained (mean 102% of controls), but petiole length decreased (mean 84% of controls). Petiole length was the most plastic trait. Seed size, seedling traits, maturity duration and eco-geographic variables at site of origin were not related to waterlogging tolerance.ConclusionsWide variation in waterlogging tolerance exists within ssp. yanninicum. Petiole length reduction, an easy-to-measure and non-destructive indicator, could be used as a preliminary selection tool when screening large numbers of ssp. yanninicum for waterlogging tolerance in a breeding program.

Large variation in waterlogging tolerance and recovery among the three subspecies of Trifolium subterranean L. is related to root and shoot responses

Tolerance to waterlogging and recovery ability was compared among the three subspecies of subterranean clover (Trifolium subterraneum L.) to identify tolerance mechanisms, in order to guide future subclover breeding activities. Three cultivars each of ssp. yanninicum, subterraneum and brachycalycinum were grown in a controlled environment glasshouse with T. michelianum as a waterlogging-tolerant control. After 28 days of growth two treatments were imposed for 35 days: free-draining (control) and waterlogged. A 21-day recovery period followed. After 35 days, waterlogging reduced shoot dry weight (DW) to 58–27% and root DW to 35–21% of respective controls in each subspecies. Shoot relative growth rate (RGR) of yanninicum was least affected (78–104% of control), compared to subterraneum (51–100%) and brachycalycinum (45–69%). The subterraneum cv. Denmark had a similar response to subspecies yanninicum. Shoot RGR of T. michelianum was 138% of its control. After recovery, all traits (except tap root length) recovered to control values. Up to 21 days, the main traits associated with waterlogging tolerance (shoot and root growth) were high petiole length, less petiole anthocyanin pigmentation and high leaf chlorophyll content, but by 35 days these were a high proportion of leaf biomass, high stomatal conductance and enhanced root porosity. Average root diameter and nodulation rates were unrelated to waterlogging tolerance. Subspecies yanninicum had superior waterlogging tolerance. Priority traits for easily-assessed indicators of waterlogging tolerance are less reduction of leaf size and high stomatal conductance.

TEMPERATURE AND DROUGHT STRESS EFFECTS ON GROWTH AND DEVELOPMENT OF BAMBARA GROUNDNUT (VIGNA SUBTERRANEA L.)

SUMMARYThe effect of drought and temperature on the growth and development of bambara groundnut (Vigna subterranea (L.) Verdc.) was studied in controlled environment glasshouses in the United Kingdom. There were two landraces, S19-3 (from a hot, dry environment; Namibia) and Uniswa Red (from a cool, wet environment; Swaziland), two temperature regimes (23 °C and 33 °C) and three watering regimes (2006; fully irrigated), 2007 (drought imposed at 77 days after sowing (DAS)) and 2008 (drought imposed at 30 DAS)). Bambara groundnut responded to drought by slowing the rate of leaf area expansion and reducing final canopy size and total dry matter (TDM). Drought also caused significant reductions in pod dry matter, pod numbers and harvest index (HI), leading to a decrease in final yield that was different between landraces. Throughout the three growing seasons, landraces grown at 33 °C produced more TDM than the landraces grown at 23 °C. The two landraces differed in their phenology; S19-3 exhibited a reduced phenology where leaf numbers started to decrease before Uniswa Red at both temperatures, while Uniswa Red maintained the longest life cycle. The lowest pod yield was produced by Uniswa Red in 2008 at 33 °C (maximum of 35.5 gm−2), while S19-3 produced a minimum pod yield of 56.6 gm−2 at 33 °C, also in 2008. However, both landraces produced considerably more pod yield at 23 °C throughout the three growing seasons (minimum of 151 gm−2 and 162 gm−2 for Uniswa Red and S19-3, respectively). Under moderate drought, S19-3 at 33 °C gave the highest pod yield (365 gm−2) among the treatments throughout the three growing seasons and maintained HI better under drought. Despite being from a hot, dry environment, S19-3 also performed well at low temperature, which indicates the adaptation of S19-3 to low temperature that it also experiences in the country of origin.

The effect of elevated atmospheric carbon dioxide concentration on the contribution of residual legume and fertilizer nitrogen to a subsequent wheat crop

This study investigated the residual contribution of legume and fertilizer nitrogen (N) to a subsequent crop under the effect of elevated carbon dioxide concentration ([CO2]). Field pea (Pisum sativum L.) was labeled in situ with 15N (by absorption of a 15N-labeled urea solution through cut tendrils) under ambient and elevated (700 μmol mol–1) [CO2] in controlled environment glasshouse chambers. Barley (Hordeum vulgare L.) and its soil were also labeled under the same conditions by addition of 15N-enriched urea to the soil. Wheat (Triticum aestivum L.) was subsequently grown to physiological maturity on the soil containing either 15N-labeled field pea residues (including 15N-labeled rhizodeposits) or 15N-labeled barley plus fertilizer 15N residues. Elevated [CO2] increased the total biomass of field pea (21 %) and N-fertilized barley (23 %), but did not significantly affect the biomass of unfertilized barley. Elevated [CO2] increased the C:N ratio of residues of field pea (18 %) and N-fertilized barley (19 %), but had no significant effect on that of unfertilized barley. Elevated [CO2] increased total biomass (11 %) and grain yield (40 %) of subsequent wheat crop regardless of rotation type in the first phase. Irrespective of [CO2], the grain yield and total N uptake by wheat following field pea were 24 % and 11 %, respectively, higher than those of the wheat following N-fertilized barley. The residual N contribution from field pea to wheat was 20 % under ambient [CO2], but dropped to 11 % under elevated [CO2], while that from fertilizer did not differ significantly between ambient [CO2] (4 %) and elevated [CO2] (5 %). The relative value of legume derived N to subsequent cereals may be reduced under elevated [CO2]. However, compared to N fertilizer application, legume incorporation will be more beneficial to grain yield and N supply to subsequent cereals under future (elevated [CO2]) climates.

Effects of salt accumulation on the leaf water potential and transpiration rate of pot-grown wheat with a controlled saline groundwater table

We investigated the effects of continuous salt accumulation in the root zone of wheat. Leaf water potential and transpiration rate were measured in plants grown in an experimental pot system. Plants were grown in a controlled-environment glasshouse in sand-filled pots, in which the groundwater table was maintained at a desired depth. Saline water was recharged from the base, providing constant water content in the unsaturated root zone. At 52 days after sowing, the water table was set at a depth of 47 cm from the soil surface. Groundwater and initial soil water were replaced with saline water with electrical conductivities (EC) of 0.2 dS m−1 (Control [C]), 8 dS m−1 (EC8) and 16 dS m−1 (EC16). The daily transpiration rate, leaf water potential (ψL ) and EC of the soil water at a depth of 45 cm were measured during the experiment. Stomatal behavior was expressed using the transpiration ratio E t /E tc (the ratio of the transpiration rates of EC8 and EC16 to that in the control). Our results indicated that ψL and E t /E tc gradually decreased with increasing soil water EC as a result of transpiration and water uptake by the roots. The final ψL values of EC8 and EC16 were –4.0 MPa and –7.0 MPa, respectively, and the final E t /E tc values of EC8 and EC16 were 0.3 and 0.2, respectively. E t /E tc decreased with decreasing ψL , and induced stomatal closure. The E t /E tc of the wheat was 0.5 when ψL was –2.5 MPa and 0.3 when ψL was –3.0 MPa. Although a reduction in ψL from –1.5 MPa to –3.0 MPa caused a steep decline in E t /E tc , a subsequent reduction of ψL to –7.0 MPa caused only a minor reduction. This relationship between stomatal behavior and salt accumulation is similar to that reported in previous studies for plants grown in drought conditions. Changes in the transpiration ratio were expressed in an empirical equation as a function of ψL .

A validated mechanistic model of carrot ( Daucus carota L.) growth

A mechanistic model of carrot vegetative and root development was constructed. This model determined canopy photosynthesis over a day, assimilates were then partitioned into either roots or leaves via temperature dependent partitioning coefficients. Assimilates were lost via terms describing growth and maintenance respiration. The model was calibrated on data from four different carrot cultivars, originating from the UK (Autumn King), Syria (Carrot S), Poland (Dolanka) and Russia (Hibinskaja), grown in controlled environment glasshouse compartments at one of six temperatures (9–30 °C) repeated over three sowing dates. Calibration of the model showed that it could account for between 83 and 95% of the variance in carrot plant and root dry weights. The model was then validated using independent data from the same cultivars of carrots grown in the field at Reading. In this instance, the model accounted for 75 and 79% of the variance in plant and root weight, respectively. Two other independent data sets were used to validate the model, including carrot of a different cultivar (Panther) grown in phytotrons at temperatures between 9 and 21 °C, at two different locations and over a three sowing dates. In this instance, the model accounted for between 63 and 69% of the variance in root weight. The model also predicted that if ambient carbon dioxide levels increased from 348 to 551 μmol mol −1, root dry weight would increase by 12%, which is within the margin of error of the experimental value of 16% reported in the literature. The model can therefore be used to study the potential impacts of global climate change on carrot production, as well as to rapidly predict whether germplasm is suited to any particular environment.

Growth and development of bambara groundnut ( Vigna subterranea) in response to soil moisture : 1. Dry matter and yield

The effect of drought on the growth and development of bambara groundnut ( Vigna subterranea (L.) Verdc.) was studied in controlled-environment glasshouses in the UK. There were three landraces (S19-3, DipC and UN from Namibia, Botswana and Swaziland, respectively) and two watering regimes; a control that was irrigated weekly to 90% field capacity and a drought treatment with no irrigation from 49 days after sowing (DAS) until final harvest (147 DAS). Bambara groundnut responded to drought by reducing the rate of leaf area expansion, final canopy size and total dry matter (TDM) during vegetative growth. Drought also caused significant reductions in pod dry matter (PDM), pod number, seed weight and harvest index (HI), leading to a decrease in final pod yield that was different between landraces. Across landraces, drought reduced mean pod yield from 298 g m −2 to 165 g m −2, representing 45% yield loss. Despite the reduction in all landraces, the mean pod yield across the droughted treatments that had received no water for almost 100 days indicated the resilience of the species to drought. The three landraces differed in their phenology; S19-3 exhibited a reduced phenology while UN maintained the longest life cycle. The different responses of the landraces reflect their adaptation to their local climates where mean annual rainfall ranges between 365 mm (Namibia) and 1390 mm (Swaziland). We discuss the significance of these results for future breeding programmes on bambara groundnut.

Effect of temperature on seed and fruit development in three mango ( Mangifera indica L.) cultivars

The effect of diurnal maximum/minimum (20/10 or 25/15 °C) temperatures on seed and fruit development of ‘Irwin’, ‘Kensington’ and ‘Nam Dok Mai’ mangoes ( Mangifera indica L.) was studied in a controlled-environment glasshouse. Exposure to low temperatures (20/10 °C day/night) 3 days after hand pollination significantly increased the percentage of stenospermocarpic fruit (nubbins), in which embryos were aborted at some stage during early fruit development. There were significant differences between cultivars in the percentage of nubbins produced out of the total fruit set following overnight exposure to 10 °C with 21% for ‘Nam Dok Mai’, 11% for ‘Kensington’ and 3% for ‘Irwin’. At 45 days after pollination, nubbin fruits were much smaller in size and weighed ca. 50% less than normal fruits. The lower percentage of nubbin fruits in ‘Irwin’ implies a greater adaptation to cool temperatures by this cultivar during fruit set and early embryo development.

The effects of temperature and light integral on early vegetative growth and chlorophyll fluorescence of four contrasting genotypes of cacao (Theobroma cacao)

SummaryThe effect of temperature on early vegetative growth, leaf chlorophyll fluorescence and chlorophyll content was examined on four genotypes of cacao (Amelonado, AMAZ 15–15, SCA 6 and SPEC 54/1). A controlled environment glasshouse was used to simulate the temperature conditions of three cacao‐growing regions (Bahia, Brazil; Tafo, Ghana and Lower Perak, Malaysia) over the course of a year. Base temperatures calculated from increments in main stem growth varied from 18.6°C for AMAZ 15/15 to 20.8°C for SPEC 54/1. Temporal variation in Fv/Fm observed for two of the clones (SCA 6 and SPEC 54/1) in two of the compartments were correlated with temperature differences over time. Significant differences were also recorded between genotypes in leaf chlorophyll content. It was shown that variation over time in leaf chlorophyll content could be quantified accurately as a function of temperature and light integral. The results imply that genetic variability exists in cacao in response to temperature stress.

Pod set related to photosynthetic rate and endogenous ABA in soybeans subjected to different water regimes and exogenous ABA and BA at early reproductive stages.

The physiological reasons for reduced pod set in soybean (Glycine max) caused by drought during anthesis are not established. The objective of this study was to investigate the involvement of photosynthetic rate (A), pod endogenous abscisic acid (ABA) and exogenously applied ABA and 6-benzylaminopurine (BA) in regulating pod set in soybean during drought. Two pot experiments were done in a controlled-environment glasshouse. In expt I, soybeans were either well-watered (WW) or droughted by withholding water from 4 d before to 4 d after anthesis (DAA). In expt II, soybeans were drought-stressed (DS) from -4 to 4 DAA. From -2 to 4 DAA, some of the WW and DS plants were treated with 0.1 mm ABA or 1 mm BA. Drought stress decreased A, but increased pod ABA concentration ([ABA]). Pod set decreased only when A had decreased by 40 %, and pod [ABA] had increased 1.5-fold. Beyond the thresholds, pod set correlated positively with A and negatively with pod [ABA]. Exogenously applied ABA decreased A and pod set in WW plants, whilst it increased A and pod set in DS plants; exogenous BA had opposite effects. In these plants, pod set correlated linearly with A. Drought-induced decrease in A is significant in inducing pod abortion, probably as a consequence of carbohydrate deprivation. The effects of ABA and BA on pod set may be partially due to their effects on photosynthate supply.

Physical strength and its relation to leaf anatomical characteristics of nine forage grasses

Nine species of forage grasses (five C3 species and four C4 species) were planted in a controlled-environment glasshouse. The C3 plants were Festuca arundinacea Schreb, Dactylis glomerata L., Phleum pratense L., Lolium perennel L. and Poa pratensis L.; the C4 plants were Chloris gayana Kunch., Cynodon dactylon (L.) Pers., Paspalum dilatatum Poir. and Sorghum halenpense (L.) Pers. The number of major vascular bundles and minor vascular bundles, cross-sectional area, the area and proportion of sclerenchyma in a cross-section, thickness of leaf blade, and tensile and shear strength were investigated in order to determine the relationship between physical strength and anatomical characteristics. Physical strength and anatomical characteristics of leaf blades showed significant (P &lt; 0.01) variation between species. Significant correlations were detected between tensile strength and cross-sectional area in forage grasses except Festuca arundinacea. Festuca arundinacea, Dactylis glomerata, Phleum pratense, Chloris gayana and Sorghum halenpense showed significant correlations of tensile strength with the number of major vascular bundles. Festuca arundinacea, Dactylis glomerata and Lolium perennel showed significant correlations of shear strength with cross-sectional area. Festuca arundinacea, Dactylis glomerata and Paspalum dilatatum showed significant correlations of shear strength with the number of major vascular bundles. The proportion of sclerenchyma in a cross-section showed poor correlations with tensile and shear strength. Thickness of leaf blade showed poor correlations with tensile and shear strength except in Dactylis glomerata. Physical strength and anatomical characteristics of leaf blades of the C3 group differed significantly (P &lt; 0.01) when compared with the C4 group except for cross-sectional area. Tensile and shear strength showed significant correlations with cross-sectional area, sclerenchyma area and the number of vascular bundles when all nine species were treated as one group.

Effects of elevated CO2, drought and temperature on the water relations and gas exchange of groundnut(Arachis hypogaea)stands grown in controlled environment glasshouses

Stands of groundnut (Arachis hypogaeaL. cv. Kadiri‐3) were grown in controlled environment glasshouses at mean atmospheric CO2concentrations of 375 or 700 μmol mol−1and daily mean air temperatures of 28 or 32°C on irrigated or drying soil profiles. Leaf water (Ψl) and solute potential (Ψs), relative water content (RWC), stomatal conductance (gl) and net photosynthesis (Pn) were measured at midday for the youngest mature leaf throughout the growing season. Elevated CO2and temperature had no detectable effect on the water relations of irrigated plants, but higher values of RWC, Ψland Ψswere maintained for longer under elevated CO2during progressive drought. Turgor potential (Ψp) reached zero when Ψldeclined to −1.6 to −1.8 MPa in all treatments; turgor was lost sooner when droughted plants were grown under ambient CO2. A 4°C increase in mean air temperature had no effect on Ψsin droughted plants, but elicited a small increase in Ψl; midday glvalues were lower under elevated than under ambient CO2, and Ψland gldeclined below −1.5 MPa and 0.25 cm s−1, respectively, as the soil dried. Despite the low glvalues recorded for droughted plants late in the season, Pnwas maintained under elevated CO2, but declined to zero 3 weeks before final harvest under ambient CO2. Concurrent reductions in gland increases in water use efficiency under elevated CO2prolonged photosynthetic activity during drought and increased pod yields relative to plants grown under ambient CO2. The implications of future increases in atmospheric CO2for the productivity of indeterminate C3crops grown in rainfed subsistence agricultural systems in the semi‐arid tropics are discussed.

EFFECT OF TEMPERATURE ON INFLORESCENCE DEVELOPMENT AND FLORAL BIOLOGY OF MANGO (MANGIFERA INDICA L.)

Trees of two mono-embryonic (‘Irwin’ and ‘Sensation’) and two poly-embryonic (‘Nam Dok Mai’ and ‘Kensington’) mango cultivars were exposed to winter temperatures to induce flowering. They were subsequently transferred into controlled environment glasshouse rooms under day/night temperature regimes of 15/5, 20/10, 25/15 and 30/20°C for 20 weeks. Inflorescence development only occurred on trees that were maintained at 20/10, 25/15 and 30/20°C. Higher temperatures generally increased the inflorescence size while there was an inverse effect on the mean number of flowers per inflorescence with 619.6 at 20/10°C decreasing to 431.3 at 30/20°C. There was an inverse relationship between the length of the anthesis period and temperature. Low temperatures at 20/10°C decreased the percent hermaphrodite flowers in poly-embryonic cultivars but increased the percentages in mono-embryonic cultivars. Style length and stigma width was reduced when the trees were held at 20/10°C compared to those trees held at either 25/15 or 30/20°C. Trees of ‘Kensington’ grown at 20/10°C mainly produced flowers which had short styles (0.62 mm) and small stigmatic surfaces while ‘Nam Dok Mai’ and ‘Irwin’ trees produced some flowers which had deformed ovaries or fused ovaries. A decrease in percent hermaphrodite flowers and floral changes which occur in poly-embryonic cultivars when inflorescences develop under low temperatures (20/10°C), are likely factors contributing to their low fruit set when grown in subtropical climates.

Effect of temperature on inflorescence and floral development in four mango ( Mangifera indica L.) cultivars

To study the effect of low temperature on inflorescence and floral development of mango ( Mangifera indica L.), `Nam Dok Mai', `Kensington', `Irwin' and `Sensation' trees were exposed to natural winter temperatures to induce flowering, and then transferred to controlled-environment glasshouse rooms where day/night temperature regimes of 15/5°, 20/10°, 25/15° and 30/20°C were maintained for 20 weeks. Day/night temperatures of 15/5°C severely inhibited the emergence and elongation of inflorescences of all cultivars with inflorescence development only occurring on trees that were maintained at the warmer temperatures (20/10°, 25/15° and 30/20°C). The time taken for inflorescences to reach maximum length was 15–20 days on trees held at 25/15° or 30/20°C but extended to 54 days on trees kept at 20/10°C. Warmer temperatures generally increased the inflorescence size of all cultivars. At 20/10°C, pollen viability of `Sensation' was significantly lower than the other cultivars, but there was no significant difference between cultivars held at 25/15° and 30/20°C. Low temperatures caused morphological changes in styles, stigmas, ovaries and anther size in all cultivars, and changes were especially pronounced in `Kensington'. Style length and stigma width of all cultivars were reduced when trees were held at 20/10°C compared to trees held at either 25/15° or 30/20°C. Trees of `Kensington' grown at 20/10°C mainly produced flowers that had short styles (0.62 mm) and small stigmas (0.09 mm) while `Nam Dok Mai' and `Irwin' trees produced some flowers with deformed or fused ovaries. Scanning electron microscopic studies indicated that normal `Kensington' flowers had non-symmetrical stigmas that were covered with undeveloped papillae cells. The short-styled `Kensington' flowers (produced at 20/10°C) had a much smaller receptive stigmatic area compared to normal flowers produced at 30/20°C. Low temperature-induced (20/10°C) changes in ovary size in `Nam Dok Mai' and style length in `Kensington' flowers may contribute to low fruit set in these two cultivars when grown in subtropical climates.

The effect of soil moisture on light interception and the conversion coefficient for three landraces of bambara groundnut (Vigna subterranea)

Three landraces of bambara groundnut (Vigna subterranea (L.) Verdc.) were grown as crop stands in controlled environment glasshouses at the Tropical Crops Research Unit, University of Nottingham, in 1995. Two soil moisture treatments were imposed: irrigated to 90% field capacity each week and irrigated to 60% field capacity until establishment (27 days after sowing) with no further irrigation. Seasonal mean fractional interception varied between 0·20–0·37 for the droughted treatments and 0·62–0·74 for the irrigated treatments, resulting in cumulative intercepted radiation of 228–350 MJ/m2 and 662–794 MJ/m2, respectively. The maximum total dry matter (DM) produced was 5·8 t/ha at final harvest (145 days after sowing) with a pod yield of 2·7 t/ha. Under moisture stress there was little difference in DM production between landraces, with the highest total DM of 1·1 t/ha and a pod yield of 0·05 t/ha, representing a harvest index of 0·05 compared with an average of 0·46 for the irrigated treatments. The conversion coefficient was reduced from 1·00 under irrigation to 0·51 g DM/MJ radiation intercepted by soil moisture stress. Two of the landraces showed adaptive mechanisms to avoid drought; these are discussed in relation to maximizing seasonal radiation interception.

Differences in the Effects of Temperature and Photoperiod on Progress to Flowering among Diverse Mucuna spp.

The use of Mucuna spp. in cover crop and green manure technologies is proving to be successful in the tropics and subtropics following intensive efforts in technology transfer to farmers by NGOs (Non-Governmental Organizations). This includes the transfer of seeds of Mucuna spp. for which the range of adaptation and the effect of environment on crop phenology are poorly understood. A selection of Mucuna spp. germplasm was evaluated over a range of contrasting photothermal conditions in controlled-environment glasshouses. Dates of emergence and first flowering were recorded. Where possible, triple-plane rate of development models were fitted to the first flowering data to quantify the relative sensitivity of each species to photoperiod and temperature. All accessions showed short-day responses but there were substantial differences in the sensitivity of rate of progress to first flowering to environment, particularly to photoperiod. This results in differences in maturity period between accessions which, with appropriate understanding, could be functionally exploited by NGOs and NARS. However, if ignored, it could result in the promotion and use of accessions ill adapted to the environment in which they are tested. In consequence there might be unnecessary resistance from farmers to the adoption of green manure and cover crops technologies which are vital to the design and maintenance of sustainable farming systems in low-income countries in the tropics.

Effect of temperature on inflorescence development and sex expression of mono- and poly-embryonic mango (Mangifera indica L.) cultivars

SummaryThe effect of temperature on inflorescence development and sex expression in two mono-embryonic (`Irwin' and `Sensation'), and two poly-embryonic (`Nam Dok Mai' and `Kensington') mango cultivars was studied. Trees were subjected to natural winter temperatures to induce flowering prior to transfer into controlled environment glasshouse rooms under day/night temperature regimes of 15/5, 20/10, 25/15 and 30/208C for 20 weeks. Inflorescence development did not progress when trees were held at 15/58C. Cooler temperatures (20/108C) delayed the start of anthesis (42.4.d) compared with trees grown at 25/158C (23.d) and 30/208C (16.1.d). At 20/108C, the delay in the start of anthesis was greatest for `Sensation' (55.5.d) and least for `Nam Dok Mai' (25.5.d) while at other temperatures there was little difference between cultivars. The distribution of hermaphrodite flowers within the inflorescence was independent of temperature with the highest percentage found in the apical half of the inflorescence. There was an inverse relationship between the length of the anthesis period and temperature, with anthesis occurring over 30.d at 20/108C and reducing to fewer than 10.d at 30/208C. Temperature also had an inverse effect on the total number of flowers per inflorescence with 619.6.6.108.0 (mean for all cultivars) at 20/108C decreasing to 431.3.6.80.5 at 30/208C.

Leaf Gas Exchange, Dry Matter Partitioning, and Mineral Element Concentrations in Mango as Influenced by Elevated Atmospheric Carbon Dioxide and Root Restriction

The effects of atmospheric CO2 enrichment and root restriction on net CO2 assimilation (A), dry mass partitioning, and leaf mineral element concentrations in `Kensington' and `Tommy Atkins' mango (Mangifera indica L.) were investigated. Trees were grown in controlled-environment glasshouse rooms at ambient CO2 concentrations of 350 or 700 μmol·mol-1. At each CO2 concentration, trees were grown in 8-L containers, which restricted root growth, or grown aeroponically in 200-L root mist chambers, which did not restrict root growth. Trees grown in 350 μmol·mol-1 CO2 were more efficient at assimilating CO2 than trees grown in 700 μmol·mol-1 CO2. However, total plant and organ dry mass was generally higher for plants grown at 700 μmol·mol-1 CO2 due to increased A as a result of a greater internal partial pressure of CO2 (Ci) in leaves of plants in the CO2 enriched environment. Root restriction reduced A resulting in decreased organ and plant dry mass. In root-restricted plants, reduced A and dry matter accumulation offset the increases in these variables resulting from atmospheric CO2 enrichment. Atmospheric CO2 enrichment and root restriction did not affect dry mass partitioning. Leaf mineral element concentrations were generally lower for trees grown at the higher ambient CO2 concentration, presumably due to a dilution effect from an increased growth rate.