Outdoor-grown Plants Research Articles

Comparative Transcriptome Analysis in Taraxacum koksaghyz to Identify Genes that Determine Root Volume and Root Length.

The Russian dandelion (Taraxacum koksaghyz, family Asteraceae) produces large amounts of natural rubber in the laticifers of its roots. This species has been proposed as an alternative source of natural rubber to augment or partly replace the rubber tree (Hevea brasiliensis) but domestication would require genetic improvement to increase rubber yields and agronomic optimization to facilitate harvesting and processing. Optimization has focused thus far on the size and shape of the roots, the primary storage organ for natural rubber and inulin. However, the corresponding genetic factors are poorly understood. Here we describe the comparative transcriptomic analysis of root tissues from T. koksaghyz plant sets featuring different root sizes and shapes, aiming to identify differentially expressed genes correlating with root length or root diameter in the upper root and root tip. The resulting datasets revealed multiple candidate genes for each trait and root part, including a glucan endo-1,3-β-d-glucosidase, an allene oxide synthase 3, and a TIFY10A/JAZ1 homolog. These three genes were tested by qRT-PCR in outdoor-grown plants with diverse root morphology, and the expression of two genes correlated with the appropriate root morphotype, confirming the effectiveness of our method. We evaluated the candidate genes to gain insight into their potential functions in root development. Such candidate genes could be suitable for marker-assisted breeding programs in the future.

The first report on the occurrence race 9 of the tomato leaf mold pathogen Cladosporium fulvum (syn. Passalora fulva) in Cuba

Leaf mold caused by the fungus Cladosporium fulvum (syn. Passalora fulva) has been a serious disease in greenhouse tomatoes in Cuba, but less damage is seen in outdoor grown plants. This study was conducted to identify races of the causal agent of tomato leaf mold. A total of 36 single conidial isolates obtained from different provinces in Cuba and the reference strain race 0 were inoculated on a differential set of tomato cultivars carrying different Cf resistance genes. Further, a polymerase chain reaction (PCR) was developed using Avr9 gene-specific primers. As result, all isolates could overcome the Cf-9 resistance gene only, but not resistance genes Cf-2, Cf-4 and Cf-5 and must therefore be coined race 9. Race identity was also confirmed by PCR analysis, which showed that the Avr9 gene was not amplified in any of 36 single conidial isolates studied proving that they all lack this gene. This is the first report of the occurrence of race 9 of C. fulvum in Cuba. Pyramiding other Cf genes in hybrid of tomato may provide a more durable level of resistance to C. fulvum.

The Morphological and Anatomical Traits of the Leaf in Representative Vinca Species Observed on Indoor- and Outdoor-Grown Plants

Morphological and anatomical traits of the Vinca leaf were examined using microscopy techniques. Outdoor Vinca minor and V. herbacea plants and greenhouse cultivated V. major and V. major var. variegata plants had interspecific variations. All Vinca species leaves are hypostomatic. However, except for V. minor leaf, few stomata were also present on the upper epidermis. V. minor leaf had the highest stomatal index and V. major had the lowest, while the distribution of trichomes on the upper epidermis was species-specific. Differentiated palisade and spongy parenchyma tissues were present in all Vinca species’ leaves. However, V. minor and V. herbacea leaves had a more organized anatomical aspect, compared to V. major and V. major var. variegata leaves. Additionally, as a novelty, the cellular to intercellular space ratio of the Vinca leaf’s mesophyll was revealed herein with the help of computational analysis. Lipid droplets of different sizes and aspects were localized in the spongy parenchyma cells. Ultrastructural characteristics of the cuticle and its epicuticular waxes were described for the first time. Moreover, thick layers of cutin seemed to be characteristic of the outdoor plants only. This could be an adaptation to the unpredictable environmental conditions, but nevertheless, it might influence the chemical composition of plants.

First Report of Hemp Leaf Spot Caused by a Bipolaris Species on Hemp (Cannabis sativa) in Kentucky

Upon reintroduction of hemp (Cannabis sativa) in 2014, reports of a leaf spot disease became increasingly common in Kentucky. Outdoor-grown plants became severely affected with necrosis and blight symptoms, and many crops were rejected by processors either as a result of leaf and bud necrosis or as a result of reduced levels of cannabidiol. Morphological data and sequences of ITS and partial 28S rDNA identified the pathogen as Drechslera gigantea. Phylogenetic analysis grouped all isolates in a clade within Bipolaris. Dicot and monocot weed hosts within symptomatic fields were also identified. We refer to the disease as Bipolaris leaf spot, but the common reference is hemp leaf spot. This is the first report of a Bipolaris pathogen infecting C. sativa. Widespread distribution, disease severity, and extreme yield losses makes this one of the most important diseases of hemp in Kentucky.

Time-course accumulation of flavonoids in hydroponically grown Achillea millefolium L.

Pedneault, K., Dorais, M., Leonhart, S., Angers, P. and Gosselin, A. 2014. Time-course accumulation of flavonoids in hydroponically grown Achillea millefolium L. Can. J. Plant. Sci. 94: 383-395. In recent decades, the use of plant-based medicines as health products has increased considerably all over the world. As greenhouse hydroponic culture allows standardized cultural methods to be used, it may be valuable for reducing the risks associated with harvesting medicinal plants from the wild, such as species dissemination, species misidentification, adulteration, and non-hygienic handling, while allowing the production of high yields of clean, standardized biomass year-round. To evaluate the potential of hydroponic culture for medicinal plant production, the present study investigated the accumulation patterns of apigenin, luteolin, apigenin glycosides, and the chlorogenic acid 5-caffeoylquinic acid in the plant organs of A. millefolium at five phenological stages from 35 to 102 d after sowing, and drew a comparison with outdoor-grown plants at 122 d after sowing. The results showed two flavonoid accumulation peaks: one at the early growth stage (35 d after sowing) and one at early flowering (87 d after sowing). At 87 d after sowing, most of the apigenin glycosides were concentrated in the roots (3.80% wt/wt, dry weight basis), whereas free apigenin and luteolin were located mainly in the flower heads (1.25 and 0.86% wt/wt, dry weight basis, respectively). Early flowering was the best harvesting stage for optimal flavonoid production in terms of active compounds per plant and kilograms of plant biomass per cultivated area. At 122 d after sowing (phenological stage 4), the outdoor-grown plants were nine times smaller than the early flowering plants (87 d after sowing) from the hydroponic system and had a root-tissue apigenin glycoside level that was five times lower than that of the hydroponically grown plants. In conclusion, the use of a hydroponic growing system reduced by 29% the time required to reach phenological stage 4, which corresponds to maximum plant bioactive concentration, in comparison with field production. Therefore, hydroponic culture represents an effective alternative to outdoor production and can result in standardized, high-quality medicinal plant biomass with potential flavonoid yields approximating 515 mg per plant.

Time-course accumulation of flavonoids in hydroponically grown Achillea millefolium L.

Pedneault, K., Dorais, M., Léonhart, S., Angers, P. and Gosselin, A. 2014. Time-course accumulation of flavonoids in hydroponically grown Achillea millefolium L. Can. J. Plant. Sci. 94: 383–395. In recent decades, the use of plant-based medicines as health products has increased considerably all over the world. As greenhouse hydroponic culture allows standardized cultural methods to be used, it may be valuable for reducing the risks associated with harvesting medicinal plants from the wild, such as species dissemination, species misidentification, adulteration, and non-hygienic handling, while allowing the production of high yields of clean, standardized biomass year-round. To evaluate the potential of hydroponic culture for medicinal plant production, the present study investigated the accumulation patterns of apigenin, luteolin, apigenin glycosides, and the chlorogenic acid 5-caffeoylquinic acid in the plant organs of A. millefolium at five phenological stages from 35 to 102 d after sowing, and drew a comparison with outdoor-grown plants at 122 d after sowing. The results showed two flavonoid accumulation peaks: one at the early growth stage (35 d after sowing) and one at early flowering (87 d after sowing). At 87 d after sowing, most of the apigenin glycosides were concentrated in the roots (3.80% wt/wt, dry weight basis), whereas free apigenin and luteolin were located mainly in the flower heads (1.25 and 0.86% wt/wt, dry weight basis, respectively). Early flowering was the best harvesting stage for optimal flavonoid production in terms of active compounds per plant and kilograms of plant biomass per cultivated area. At 122 d after sowing (phenological stage 4), the outdoor-grown plants were nine times smaller than the early flowering plants (87 d after sowing) from the hydroponic system and had a root-tissue apigenin glycoside level that was five times lower than that of the hydroponically grown plants. In conclusion, the use of a hydroponic growing system reduced by 29% the time required to reach phenological stage 4, which corresponds to maximum plant bioactive concentration, in comparison with field production. Therefore, hydroponic culture represents an effective alternative to outdoor production and can result in standardized, high-quality medicinal plant biomass with potential flavonoid yields approximating 515 mg per plant.

Temperature impacts changes in crown buds and flowering of gentian ‘Spotlight’

A better understanding of the origin and development of crown buds in gentian may help explain the observed spread in timing of flower harvest maturity. The types and numbers of buds, the time of their macroscopic appearance, emergence and development to flowering were tracked over time, in two growing environments for two growth cycles of the gentian cultivar ‘Spotlight’. Although different types of buds were present, only pre-formed primary-crown buds produced flowering shoots. In the first growth cycle, only 73% of these pre-formed buds emerged, leaving the rest of the buds to senesce and degenerate. Hence, the observed spread in time of flower harvest maturity was not due to either bud type or buds that appeared during the current growth cycle developing into floral shoots. The appearance of new crown buds for the following growth cycle's flower production occurred over an 8-month period, from summer through to winter. The time of harvest maturity for a shoot was not strongly correlated with the time of bud appearance or shoot emergence, as originally hypothesised. Compared with those grown in the cooler environment outside, cultivation in a protected environment resulted in 50% longer shoots at harvest, did not influence the time to flower harvest, but increased the rate of appearance of buds by an additional 0.18 per month. With no chilling however, within the protected environment the crown buds failed to emerge as shoots during the second growth cycle. In contrast, with chilling received by outdoor-grown plants, crown buds emerged and flowered. The lack of any correlation between the time of appearance of buds and/or their emergence with that of stem harvest maturity, as well as the chilling requirement for shoot emergence, highlights that factors associated with growth and development of a crown bud after its appearance may have a greater influence on the time of harvest maturity in ‘Spotlight’ and, therefore, the spread in timing.

A comparative study of the antimicrobial and phytochemical properties between outdoor grown and micropropagated Tulbaghia violacea Harv. plants

The study aimed to compare the antimicrobial and phytochemical properties of in vitro cultured and outdoor grown Tulbaghia violacea plants in the quest to validate the use of micropropagated plants as alternatives to outdoor grown plants in traditional medicine. Tulbaghia violacea is used extensively in South African traditional medicine for HIV/AIDS patients and in the treatment of gastrointestinal ailments, asthma, fever and tuberculosis. Extracts of micropropagated and outdoor grown Tulbaghia violacea plants were evaluated for their antibacterial and antifungal activities against Bacillus subtilis, Escherichia coli, Klebsiella pneumoniae, Staphylococcus aureus and a fungus Candida albicans using microdilution methods. Saponins and phenolic compounds including condensed tannins, gallotannins and flavonoids were quantitatively determined using spectrophotometric methods. A qualitative test for saponins was also carried out. The petroleum ether (PE) extracts of micropropagated plants and dichloromethane (DCM) extracts of outdoor grown plants showed good antibacterial activity, each against two bacterial test strains. PE extracts of micropropagated plants showed the best antibacterial activity with a minimum inhibitory concentration (MIC) of 0.39 mg/ml against Bacillus subtilis. Good MIC (<1mg/ml) and minimum fungicidal concentration (MFC) values of 0.78 mg/ml were only obtained in DCM extracts of outdoor grown plants. MIC and MFC values for water and ethanol extracts of both micropropagated and outdoor grown plants were similar and in the range 3.125-12.5mg/ml. Total phenolics, gallotannins, flavonoids and saponins were significantly higher in micropropagated plants than in outdoor grown ones. In all cases, the amounts of phytochemical compounds in micropropagated plants were more than twice that of outdoor grown plants except for condensed tannins. The results form a good basis for the use of Tulbaghia violacea micropropagated plants as a complement to the outdoor grown plants in traditional medicine.

THE EFFECT OF TEMPERATURE AND PHOTOPERIOD ON THE LEAF SENESCENCE AND PARTITIONING OF ASTILBE AND PAEONIA

The effect of temperature and photoperiod on leaf senescence and partitioning were studied in Fall 2004 using Astilbe simplicifolia `praecox alba' and Paeonia hybrid `Barrington Belle' and Fall 2005 using Paeonia Paula Fay and Astilbe chinensis ×purpurea. Bare root divisions and crowns were potted and grown outdoors during the spring and summer. Plants were treated to either Ithaca fall outdoor and controlled warm (70–60 °F) environment under normal daylength (about 12 hours) or longday (LD15 hours in 2004 and 16 hours in 2005). The chlorophyll readings and senescing leaves were significantly affected by treatments in the two plants in 2004. There was no significant difference in the change in the total dry biomass in Paeonia hybrid `Barrington Belle' grown under different treatments but the number of large buds was highest in those grown at 70–60 °F at LD. Higher total plant biomass was observed over-all in Astilbe simplicifolia `praecox alba' in warmer greenhouse environment and under LD. The effect of photoperiod and its interaction with temperature were significant in weights of Astilbe simplicifolia `praecox alba' roots. Greenhouse grown plants had higher bud numbers compared to outdoor-grown plants. In 2005, Astilbe chinensis ×purpurea in the greenhouse under LD had more shoots and large buds than the other treatments. Senescing leaf and chlorophyll reading was affected by temperature and photoperiod and its interaction. Paeonia Paula Fay under LD outdoors had more large buds than those under natural photoperiod, but is similar in effect to those in the greenhouse. Results may be used to improve propagule quality, adjust crop production cycle and cultivation in different climate.

Photosynthetic characteristics and tolerance to photo-oxidation of transgenic rice expressing C(4) photosynthesis enzymes.

The photosynthetic characteristics of four transgenic rice lines over-expressing rice NADP-malic enzyme (ME), and maize phosphoenolpyruvate carboxylase (PC), pyruvate,orthophosphate dikinase (PK), and PC+PK (CK) were investigated using outdoor-grown plants. Relative to untransformed wild-type (WT) rice, PC transgenic rice exhibited high PC activity (25-fold increase) and enhanced activity of carbonic anhydrase (more than two-fold increase), while the activity of ribulose-bisphosphate carboxylase/oxygenase (Rubisco) and its kinetic property were not significantly altered. The PC transgenic plants also showed a higher light intensity for saturation of photosynthesis, higher photosynthetic CO(2) uptake rate and carboxylation efficiency, and slightly reduced CO(2) compensation point. In addition, chlorophyll a fluorescence analysis indicates that PC transgenic plants are more tolerant to photo-oxidative stress, due to a higher capacity to quench excess light energy via photochemical and non-photochemical means. Furthermore, PC and CK transgenic rice produced 22-24% more grains than WT plants. Taken together, these results suggest that expression of maize C(4) photosynthesis enzymes in rice, a C(3) plant, can improve its photosynthetic capacity with enhanced tolerance to photo-oxidation.

Enhancement of nodulation in bean (Phaseolus vulgaris) by UV-B irradiation.

Exposure of bean plants grown in the greenhouse, where UV-B is low, to ambient levels of UV-B light stimulated nodulation more than 2.5-fold. Reduction of UV-B radiation to 3% of ambient levels for outdoor-grown plants through use of Mylar filters consistently reduced nodulation by 45%. The increase in nodulation caused by UV-B was mainly due to an increase in number and size of nodules. The amounts of UV-B-absorbing compounds in roots of UV-B-exposed plants increased almost 5-fold. However, the composition of UV-B-absorbing compounds remained very similar. Exposing leaves to UV-B also significantly increased release of these compounds from roots to the medium. These results suggest that UV-B radiation enhances nodulation, and that a signal may be transported from shoot to roots to play a role in nodulation.

Ecotypic and genetic variation in poplar bark storage protein gene expression and accumulation.

Bark storage proteins (BSP) store nitrogen (N) translocated from senescing leaves in autumn, and supply reduced N for spring growth. Expression of bsp and BSP accumulation are associated with short day photoperiod. To determine if photoperiod-associated bsp expression varies among poplars native to different latitudes, Populus deltoides Bartr. clones originating from six latitudes were grown under natural conditions at a common location. Relative amounts of BSP mRNA in these clones were measured at 2-week intervals from August 7 to October 16. The date of maximum BSP mRNA accumulation was correlated with latitude of origin, and maximum accumulation of BSP mRNA occurred earlier in clones native to northern latitudes than in clones native to southern latitudes. This pattern of variation is consistent with photoperiodic responses of plants native to temperate climates. Genotypic variations in BSP accumulation, bark protein concentration and bark N concentration were compared among clones of six hybrid poplar (Populus trichocarpa Torr. and Gray x P. deltoides) full-sib families (three F(2) families, two F(1) families and one BC(1) family) after 6 weeks in a short day photoperiod and at midwinter. Significant differences in BSP accumulation occurred among clones within four of the six full-sib families after 6 weeks in a short day photoperiod and also at midwinter for outdoor-grown plants. Bark protein and bark N concentrations also varied significantly among clones within certain families. In general, the greatest variation was found in F(2) and BC(1) families. Within several families, relative BSP amounts were positively correlated with bark protein concentration and total bark N concentration. These results indicate a role of photoperiod in regulating bsp expression and demonstrate a genetic component underlying seasonal BSP accumulation. The results could have significance in selecting for clones with improved N storage capacity and N-use efficiency.

Dual-excitation FLIDAR for the estimation of epidermal UV absorption in leaves and canopies

A new FLIDAR was designed for remote quantitative assessment of epidermal UV absorption of leaves and canopies from chlorophyll (Chl) fluorescence (ChlF) measurements. The dual-excitation fluorescence light detection and ranging (DE-FLIDAR) performs a dual excitation of the Chl present in leaves, in the UV (355 nm) and visible (532 nm) part of the spectrum, the latter being used as a reference excitation not absorbed by the epidermis. Therefore, the epidermal UV absorption of vegetation can be estimated from the Chl fluorescence excitation ratio (FER), ΦF(532)/ΦF(355). Thanks to the alternated excitation by the DE-FLIDAR, the FER is immune to natural conditions in field, such as light-induced variable ChlF and leaf movement (variation of the angle of excitation). The DE-FLIDAR was used to investigate the presence of UV-absorbing compounds in individual leaves and canopies of different plant species, tobacco, pea, barley and wheat. The FER was much larger in outdoor-grown plants, indicating an accumulation of UV-absorbing compounds. We also analysed the epidermal UV absorption of the adaxial and abaxial side of tobacco leaves of different age. The logarithm of the FER showed a good agreement with the absorbance of methanolic extracts obtained from the same leaves. The presented DE-FLIDAR can perform up to three simultaneous fluorescence measurements; therefore, we could compare blue fluorescence (BR) to the epidermal UV absorption. In addition, a dual ratio, the red fluorescence (RF) to far-red fluorescence (FRF) emission ratio, excited at 355 and 532 nm, was shown to be linearly dependent on the Chl content. A mathematical model of leaf absorption and fluorescence, based on the Beer–Lambert's law, was developed to describe and analyse the fluorescence signatures obtained with the DE-FLIDAR.

Natural abundance of stable carbon and nitrogen isotopes in Cannabis sativa reflects growth conditions

Stable carbon and nitrogen isotope signatures (δ13C and δ15N) of Cannabis sativa were assessed for their usefulness to trace seized Cannabis leaves to the country of origin and to source crops by determining how isotope signatures relate to plant growth conditions. The isotopic composition of Cannabis examined here covered nearly the entire range of values reported for terrestrial C3 plants. The δ13C values of Cannabis from Australia, Papua New Guinea and Thailand ranged from –36 to –25‰, and δ 15N values ranged from –1.0 to 15.8‰. The stable isotope content did not allow differentiation between Cannabis originating from the three countries, but δ13C values of plantation-grown Cannabis differed between well-watered plants (average δ13C of–30.0‰) and plants that had received little irrigation (average δ13C of –26.4‰). Cannabis grown under controlled conditions had δ13C values of –32.6 and –30.6‰ with high and low water supply, respectively. These results indicate that water availability determines leaf 13C in plants grown under similar conditions of light, temperature and air humidity. The δ13C values also distinguished between indoor- and outdoor-grown Cannabis; indoor-grown plants had overall more negative δ13C values (average –31.8‰) than outdoor-grown plants (average –27.9‰). Contributing to the strong 13C-depletion of indoor-grown plants may be high relative humidity, poor ventilation and recycling of 13C-depleted respired CO2. Mineral fertilizers had mostly lower δ15N values (–0.2 to 2.2‰) than manure-based fertilizers (7.6 to 22.7‰). It was possible to link δ15N values of fertilizers associated with a crop site to soil and plant δ15N values. The strong relationship between soil, fertilizer, and plant δ15N suggests that Cannabis δ15N is determined by the isotopic composition of the nitrogen source. The distinct d15N values measured in Cannabis crops make δ15N an excellent tool for matching seized Cannabiswith a source crop. A case study is presented that demonstrates how δ13C and δ15N values can be used as a forensic tool.

Changes in cyclobutyl pyrimidine dimer levels in rice ( Oryza sativa L.) growing indoors and outdoors with or without supplemental UV-B radiation

We have examined the changes in the steady-state levels of cyclobutyl pyrimidine dimer (CPD) in rice plants ( Oryza sativa L.) growing indoors and outdoors with or without supplemental UV-B radiation. The CPD levels remain between 3 and 6 CPD Mb −1 throughout the day in plants grown under sunlight although the levels fluctuate. The CPD levels are slightly elevated with UV-B (1 W m −2) supplementation, but remain constant (between 5 and 8 CPD Mb −1) throughout the day. In plants grown under visible radiation in a growth chamber, the CPD levels remain constant but are lower compared with those in outdoor-grown plants; they are slightly elevated by supplementation with UV-B radiation. Under exposure to UV-B radiation without visible radiation, the CPD levels gradually increase with lengthening of the irradiation time and reach a level of approximately 35 CPD Mb −1 at dusk. However, this level decreases during the night and then increases again the next day. It is thus evident that the CPD levels are strictly maintained within constant limits throughout the day in plants growing indoors and outdoors with or without supplemental UV-B radiation. It is also found that excision repair occurs during the night in plants having higher CPD levels.

Effects of environment on the composition of epicuticular wax from kale and swede

The composition of leaf epicuticular waxes of two genotypes each of kale and swede were determined by gas chromatography-mass spectrometry. Plants were grown indoors (I) and outdoors (O) at SCRI, Scotland, and outdoors at Wädenswil in Switzerland (S). Epicuticular waxes from outdoor-grown plants (O and S) were found to have higher proportions of n-alkanes, octacosanoic acid, primary alcohols and long-chain esters but lower proportions of aldehydes, ketones, ketols and secondary alcohols than waxes from (I)-grown plants. Outdoor-grown plants were also found to have proportionally more shorter chain length compounds and indoor-grown plants proportionally more compounds of longer chain length. Variations in wax composition between genotypes of a species and between species were also observed. Differences in leaf surface wax ultrastructure, between species, and between different growth conditions were detected using scanning electron microscopy. The possible role of leaf wax chemicals in the antixenotic resistance to the turnip root fly, Delia floralis, of certain genotypes was also considered.

Stomatal Behavior and CO2 Exchange Characteristics in Amphistomatous Leaves

The possibility that differences in stomatal conductance between upper and lower surfaces of amphistomatous leaves are adaptations to differences in CO(2) exchange characteristics for the two surfaces was investigated. The ratio of upper to lower stomatal conductance was found to change little in response to light and humidity for well-watered sunflower (Helianthus annuus L.) plants. Stressing the plants (psi = -17 bars) and rewatering 1 day before gas exchange measurements reduced upper conductance more severely than lower in both indoor- and outdoor-grown plants, and caused small changes in conductance ratio with light and humidity. A similar pattern was found using outdoor grown sunflower and cocklebur (Xanthium strumarium L.) plants. Calculated intercellular CO(2) concentrations for upper and lower surfaces were always close to identical for a particular set of environmental conditions for both sunflower and cocklebur, indicating that no differences in CO(2) exchange characteristics exist between the two surfaces. By artificially creating a CO(2) gradient across the leaf, the resistance to CO(2) diffusion through the mesophyll was estimated and found to be so low that despite possible nonhomogeneity of the mesophyll, differences in CO(2) exchange characteristics for the two surfaces are unlikely. It is concluded that differences in conductance between upper and lower stomates are not adaptations to differences in CO(2) exchange characteristics.

Micropropagation of myrtle

Rapid clonal propagation of a local cultivar of myrtle ( Myrtus communis L.) was achieved in vitro using tips excised from vegetative shoots of outdoor-grown plants. Optimum shoot proliferation was obtained on a medium containing half-strength Murashige and Skoog (1962) (MS) salts plus (in mg l −1): nicotinic acid, 0.5; pyridoxine HCl, 0.5; thiamin HCl, 0.1; glycine, 2.0; inositol, 100; sucrose, 30 000; BA, 1.5; NAA, 0.1. Transfer of excised shoots to half-strength MS salts plus vitamins, and supplemented with 0.5 mg l −1 BA and either 0.4 or 0.6 mg l −1 NAA, resulted in good root development. Plants were successfully transferred to soil.

Photosynthesis, transpiration, and leaf diffusive conductance of the cassava leaf in response to water stress

The effects of short periods of water shortage on the CO2 and water vapour exchange of attached cassava (Manihot esculenta Crantz 'M Col 72') leaves were measured. Gas-exchange and leaf water potential measurements were made in outdoor grown plants previously subjected to varying periods without water. Leaf water potentials fell to between −0.61 and −1.06 MPa and net photosynthesis and transpiration rates declined as leaf water potential decreased. Estimations of the leaf internal CO2 conductance indicated that the linear relationship established between leaf water potential and net photosynthesis is dominated by, but not completely explained by, stomatal closure.