Regulated deficit irrigation in potted Dianthus plants: Effects of severe and moderate water stress on growth and physiological responses

The purpose of this study was to analyze the physiological and morphological response of carnation plants to different levels of irrigation and to evaluate regulated deficit irrigation as a possible technique for saving water through the application of controlled drought stress. Carnations, Dianthus caryophyllus L. cultivar, were pot-grown in an unheated greenhouse and submitted to two experiments. In the first experiment, the plants were exposed to three irrigation treatments: (control); 70% of the control (moderate deficit irrigation, MDI) and 35% of the control (severe deficit irrigation, SDI). In the second experiment, the plants were submitted to a control treatment, deficit irrigation (DI, 50% of the control) and regulated deficit irrigation (RDI). After 15 weeks, MDI plants showed a slightly reduced total dry weight, plant height and leaf area, while SDI had clearly reduced all the plant size parameters. RDI plants had similar leaf area and total dry weight to the control treatment during the blooming phase. MDI did not affect the number of flowers and no great differences in the colour parameters were observed. RDI plants had higher flower dry weight, while plant quality was affected by the SDI (lower number of shoots and flowers, lower relative chlorophyll content). Leaf osmotic potential decreased with deficit irrigation, but more markedly in SDI, which induced higher values of leaf pressure. Stomatal conductance (g_s) decreased in drought conditions more than the photosynthetic rate (P_n). Osmotic adjustment of 0.3 MPa accompanied by decreases in elasticity in response to drought resulted in turgor less at lower leaf water potentials and prevented turgor loss during drought periods.     

Measuring and modeling stomatal conductance of cucumber crop in solar greenhouse in Northeast China

Stomatal conductance (G_s), net photosynthesis (A_n) and environmental variables were measured from October 2006 to January 2007 under stable soil water content in solar greenhouse in Northeast China. Seventy percent of the measurements were used to parameterize the G_s models and others were used to validate these models. The diurnal variations of G_s were bimodal curves in early period and unimodal curves in latter period. The Ball–Berry model was run by using either observed A_n (B_Aobs-model) or predicted A_n (B_Apred-model), which was simulated from environmental variables. The B_Apred-model performed less successful than statistical models because of the systematic error in predicting A_n. The B_Aobs-model performed well (explained 89% of observed G_s) in the present study. Several statistical methodologies (Partial Least Square, PLS; Neural Net Analysis, NNA) were used to build models to predict G_s. PLS analysis found a high number of components, and the overall components explained 87% of the observed G_s variability. We tested four neural net models and found radial basis function network (RBF) performed the best. In most situations, measurements of photosynthesis are not available and G_s must be predicted from environmental data. In such case, we conclude that the PLS and NNA are more successful in predicting G_s of cucumber crop in solar greenhouse than the Ball–Berry model.     

Rapid seedlings regeneration from seeds and vegetative propagation with sucker and rhizome of Eremospatha macrocarpa (Mann & Wendl.) Wendl and Laccosperma secundiflorum (P. Beauv.) Kuntze

To develop efficient seedling production methods for Laccosperma secundiflorum and Eremospatha macrocarpa, a study was conducted to examine regeneration using offsets combined with several physical and chemical treatments of seeds. Offsets categorized into small, medium and large diameters, were planted in three conditions: shaded and open nursery, and greenhouse. We tested sucker from E. macrocarpa, and sucker and rhizome from L. secundiflorum. For both species, high viability percentage (ranging from 55% to 100%) were observed for small and medium suckers planted in shaded nursery and greenhouse, against less than 49% for sucker planted in open nursery. The mean seedling emergence times were estimated to 84, 77 and 75 days after planting (DAP) for small, medium and large sucker of L. secundiflorum, respectively under open nursery condition, and 76, 75, 95 DAP for small, medium and large suckers of the same species, respectively in shaded condition. Greenhouse has a significant positive effect on E. macrocarpa seedlings emergence time. For this species, the mean seedling emergence times were estimated to 43 DAP for small sucker and 76, 93 DAP for medium and large suckers. No seedling was obtained from rhizome planted in all the growing conditions tested. Concerning seed dormancy breaking, germination percentages and rates were determined for 13 treatments. The best treatments were pre-soaking unscarified seeds for 4 days in 1.01 g l⁻¹ and 0.10 g l⁻¹ KNO₃, with 79% and 68% of germination, respectively and in 3.46 × 10⁻³ g l⁻¹ GA₃ for 68% of germination. These methods are suggested to improve germination of L. secundiflorum seeds. Successful and recommended methods for E. macrocarpa are pre-soaking scarified seeds in 3.46 × 10⁻³ g l⁻¹ and 3.46 × 10⁻⁴ g l⁻¹ GA₃, 96% and 94% of germination, respectively. Dormancy, probably a combination of mechanical and chemical dormancy, is present in the two species.     

Effects of water deficit on olive trees cv. Chemlali under field conditions in arid region in Tunisia

Water scarcity in the Mediterranean basin in addition to the extension of irrigated lands is one of the main factors limiting agricultural development. The need for supplementary irrigation of the Chemlali olive cultivar (Olea europaea L.) during summer and autumn periods was investigated. Leaf water content, gas exchange parameters, fruit development and yield in rain-fed and in irrigated plants have been monitored in 12-year-old olive trees grown under environmental conditions in semi arid regions characterized by high temperatures and high light intensity. Trees were subjected to three irrigation treatments, T0, T1 and T2 corresponding respectively to 0, 33 and 66% of crop evapotranspiration (ET_c) by a drip irrigation system. The water deficit during the summer (from June to August) led to the decrease of soil moisture, leaf water content and gas exchange parameters. Irrigated trees showed the same slow activity in the three summer months as the rain-fed trees. For all treatments, net CO₂ assimilation, stomatal conductance and transpiration rates were markedly decreased by environmental conditions (high air temperature and high light intensity) during the summer period. At the partial active growth phase of the Chemlali olive cultivar (September–November), a significant re-increase in all parameters was observed. However, net photosynthesis and stomatal conductance of control plants (T0) were, respectively, 57 and 40% lower than those of plants conducted under milder water contribution (T1). The decrease of physiological activity in irrigated plants during hot and dry (summer time) and cold (winter) seasons was a clear evidence that water supply during such periods will be without a great benefit for photosynthetic activity, and thus growth, if applied under critical conditions inducing the rest phase of the plant. The non-statistically significant slight differences as well in photosynthetic performances activities (Pn, Gs and E rates), as in olive production between the two irrigated treatments will not cover the expenses of water loss when applying irrigation at 66% of ET_c especially in arid region characterized by scant and irregular rainfall. On the light of these results, we can conclude that the irrigation of this species during the vegetative growth phase (in spring and autumn), and stopping it during the olive rest phase (in summer and winter) could be recommended at least under the experimental conditions of this study; and that the contribution of 600 mm of water per year (33% of ET_c) can respond to the needs of the Chemlali olive cultivar in a semi arid region without impairing photosynthetic activity and olive production.     

An automated system for controlling drought stress and irrigation in potted plants

Efficient, automated irrigation systems, which can irrigate the substrate of potted plants to a desired level and supply those plants with just the amount of water required for normal plant growth are currently not available. These systems, if developed, could reduce wastage of irrigation water due to excess application. This subsequently could reduce leaching and run-off, and aid growers to cope with increasing regulations of water-use by state governments in the US. Here we describe an irrigation controller that irrigates a substrate to a set-point (volumetric water content, θ) and maintains θ close to that set-point for several weeks. The controller uses calibrated, dielectric moisture sensors, interfaced with a datalogger and solenoid valves, to measure the θ of the substrate every 20 min. When the θ of the substrate drops below the set-point, the controller opens a solenoid valve, which results in irrigation. The θ of the substrate is maintained near a constant level as the datalogger is programmed to increase θ by only 2–3% during each irrigation. Using this controller with bedding plants, we were able to maintain four distinct levels of θ for a prolonged period (40 days), regardless of changes in plant size and environmental conditions. The daily average θ maintained was slightly higher (within 2–3% on any particular day) than the set-point. When the θ measured and maintained by the dielectric moisture sensors was tested using measurements with another probe placed in the same container, the θ measured by both probes was found to be similar, indicating that the controller can indeed maintain θ near the target level. This controller may also have applications in stress physiology, since it allows control over the rate at which drought stress is imposed on plants.     

Copper distribution and ionic form effects for postharvest treatments of cut Acacia holosericea stems

A short postharvest life is the major constraint associated with cut Acacia flowers and foliage. Treatment with CuSO₄ (Cu²⁺) has previously been shown to improve the longevity of cut Acacia holosericea stems. Towards refining the treatments, a range of Cu²⁺ and Cu⁺ salts were assessed for relative efficacy in improving vase life and water relations of A. holosericea. Five hour pulses with the Cu²⁺ salts CuSO₄, CuCl₂, (CH₃COO)₂Cu and Cu(NO₃)₂ at 2.2 mM gave equally longer vase lives by ∼2.5-fold over deionised water (DIW) and standard tap water (STW) controls. The same Cu²⁺ salts at 0.5 mM in the vase solution also gave significantly (P < 0.05) improved vase life, relative fresh weight and water uptake compared to the DIW control. For Cu²⁺ versus Cu⁺, optimum concentrations with Cu²⁺ could not be directly compared due to the low solubility of the Cu⁺ salt CuCl. However, Cu⁺ from CuCl at 0.415 mM also had positive effects on vase life compared to the DIW control. Thus, both Cu²⁺ and Cu⁺ treatments can enhance vase life parameters for cut A. holosericea foliage. The benefits were irrespective of the counter ion and, thus, Cu²⁺ and Cu⁺per se were responsible. The most effective Cu²⁺ pulse treatment decreased stomatal conductance of phyllodes initially, but did not cause sustained stomatal closure. Cu accumulated to greater levels in basal stem and phyllode tissues than in upper stem and phyllode tissues of cut A. holosericea stems. Possible mechanisms of Cu²⁺/Cu⁺ action are discussed.     

Photosynthesis of field-grown Arracacha (Arracacia xanthorriza Bancroft) cultivars in relation to root-yield

There has been limited research on measuring potential differences in leaf gas exchange of Arracacha (Peruvian parsnip, Arracacia xanthorriza Bancroft) cultivars, as affected by different environments, as well as its relation to storage root-yield. The present paper reports field measurements of leaf CO₂ assimilation rates (A) for five contrasting cultivars grown at two different high-altitude locations. Using a design of plots chosen at random with three repetitions, commercial root production was determined in the two locations at different altitude (1580 and 1930 m). Daily leaf gas exchange was repeatedly monitored with a portable open-mode infrared gas analyzer at different times in both locations during the growth cycle. Root-yield, leaf area and dry weight were measured. Significant differences in leaf photosynthetic rate and in specific leaf area (SLA) were observed among cultivars. Cultivars with high SLA, had high CO₂ assimilation. Mean (A_n) and total (A_tot) of CO₂ assimilation and SLA were significantly correlated with storage root-yield across cultivars and locations. The three cultivars with the greatest commercial root production also had the highest maximum values for A and the highest specific leaf area, indicating that these two parameters can be used to select for highly productive cultivars of A. xanthorriza.     

The responses of photosynthetic capacity,chlorophyll fluorescence and chlorophyll content of nectarine (Prunus persica var. Nectarina Maxim) to greenhouse and field grown conditions

Three nectarine (Prunus persica var. Nectarina Maxim.) cultivars grown under solar-heated greenhouse and open-field in northwest China, were tested to evaluate their photosynthetic and chlorophyll fluorescence response to both growth conditions, and whether nectarine plants acclimate to the solar-heated greenhouse growth condition. Comparisons of light-saturated photosynthetic capacity (Amax) and CO₂-saturated photosynthetic capacity (RuBPmax) indicated that each cultivar (Z, Zao-Hongzhu; H, Hua-Guang; Y, Yan-Guang) maintained similar rates of light-saturated and CO₂-saturated carbon assimilation when grown in both conditions. The curve of diurnal variation of net photosynthetic (P_N) rate showed double peaks in open-field but single when grown in greenhouse. Compared with open-field-grown plants, a significant increase of daily average P_N was found in Z but decreased in Y in greenhouse. The diurnal variation of F_v/F_m indicate that plants grown in greenhouse experience less photoinhibition than in open-field condition. A reduction in chlorophyll (chl) a/b ratio in leaves of greenhouse grown plants with significant increase in chlorophyll (chl) b content were obtained. The results suggest that some nectarine cultivars have the ability to acclimate to the solar-heated greenhouse growth condition.     

Seed dormancy and germination of Michelia yunnanensis (Magnoliaceae)

Michelia yunnanensis Franch. is a Chinese endemic ornamental shrub with potential for greater utilization as a landscape and medicinal plant if propagation was less difficult. Seed development and breaking of seed dormancy were investigated to improve propagation of M. yunnanensis. No fresh seeds germinated when tested at the time of dispersal. Newly matured seeds of M. yunnanensis contained differentiated linear underdeveloped embryos that were physiologically dormant. The embryo/seed length ratio of M. yunnanensis was 0.15. Warm stratification did not break seed dormancy. Dormancy was broken by cold stratification at 4 °C but not by flowing water or nitrate. Embryos developed grew inside seeds during cold stratification at 4 °C. In newly harvested dormant seeds, embryos were 0.94 mm long and increased in length 139% before radicle emergence (germination). GA₃ substituted for cold stratification to break dormancy in seeds of M. yunnanensis incubated at 25 °C or 20/25 °C. Mature M. yunnanensis seeds exhibited intermediate complex morphophysiological dormancy. Optimal germination of non-dormant seed in terms of both germination percentage and rate occurred at 20/25 °C.     

Root restriction-induced limitation to photosynthesis in tomato (Lycopersicon esculentum Mill.) leaves

Root restriction often depresses photosynthetic capacity and the mechanism for this reduction, however, remains unclear. To identify the mechanism by which root restriction affects the photosynthetic characteristics, tomato (Lycopersicon esculentum Mill.) seedlings were subjected to root restriction stress with or without supplemental aeration to the nutrient solution. With the development of the root restriction stress, CO₂ assimilation rate was decreased only in confined plants without supplemental aeration. There were also significant decreases in leaf water potential, stomatal conductance (g_s), intercellular CO₂ concentration (C_i), and increases in the stomatal limitation (l) and the xylem sap ABA concentration. Meanwhile, the maximum carboxylation rate of Rubisco (V_cmax) and the capacity for ribulose-1,5-bisphosphate regeneration (J_max) also decreased, followed by substantial reductions in the quantum yield of PSII electron transport (Φ_PSII). Additionally, root restriction resulted in accumulation of carbohydrates in various plant tissues irrespective of aeration conditions. It is likely that root restriction-induced depression of photosynthesis was mimicked by water stress.     

Response of Vitis vinifera L. plants inoculated with Phaeoacremonium angustius and Phaeomoniella chlamydospora to thiabendazole,resveratrol and sodium arsenite

The effect of some pesticides (sodium arsenite, thiabendazole and ziram) and the natural phytoalexin (resveratrol) on mycelial growth of Phaeomoniella chlamydospora and Phaeoacremonium angustius was studied. Several strains of these species were grown on malt extract agar (MEA) plates containing different concentrations of inhibitory compounds and colony diameters were measured. While sodium arsenite and ziram had little effect on the growth of both species, thiabendazole inhibited colony growth, at minimum concentrations of 6 μM for Ph. chlamydospora and 15 μM for P. angustius. Resveratrol at concentrations equal to or grater than 867 μM also inhibited colony growth of both species. To assay the effect of these substances on plant response to infection, in vitro grapevines were inoculated with Ph. chlamydospora or P. angustius spores and were grown in the presence of sodium arsenite (0–30 μM), thiabendazole (0–30 μM) or resveratrol (0–876 μM). Infected untreated plants and sodium arsenite-treated plants developed symptoms of senescence (reduced growth, increased membrane lipid peroxidation, and decreased chlorophyll content and fluorescence). In contrast, infected plants treated with thiabendazole (30 μM) or with resveratrol (876 μM) showed similar characteristics of fresh weight, malondialdehyde accumulation and chlorophyll fluorescence to those of uninfected plants. These results are promising with respect to the use of thiabendazole-containing pesticides as alternatives to currently used pesticides for control of esca in vines. Results also suggest that the presence of resveratrol in grapevines may be useful to induce resistance to these fungi.     

Transpiration,photosynthetic responses,tissue water relations and dry mass partitioning in Callistemon plants during drought conditions

Callistemon is an Australian species used as ornamental plant in Mediterranean regions. The objective of this research was to analyse the ability of Callistemon to overcome water deficit in terms of adjusting its physiology and morphology. Potted Callistemon laevis Anon plants were grown in controlled environment and subjected to drought stress by reducing irrigation water by 40% compared to the control (irrigated to container capacity). The drought stress produced the smallest plants throughout the experiment. After three months of drought, the leaf area, number of leaves and root volume decreased, while root/shoot ratio and root density increased. The higher root hydraulic resistance in stressed plants caused decreases in leaf and stem water potentials resulting in lower stomatal conductance and indicating that water flow through the roots is a factor that strongly influences shoot water relations. The water stress affected transpiration (63% reduction compared with the control). The consistent decrease in g_s suggested an adaptative efficient stomatal control of transpiration by this species, resulting in a higher intrinsic water use efficiency (P_n/g_s) in drought conditions, increasing as the experimental time progressed. This was accompanied by an improvement in water use efficiency of production to maintain the leaf water status. In addition, water stress induced an active osmotic adjustment and led to decreases in leaf tissue elasticity in order to maintain turgor. Therefore, the water deficit produced changes in plant water relations, gas exchange and growth in an adaptation process which could promote the faster establishment of this species in gardens or landscaping projects in Mediterranean conditions.     

Growth and flowering of black iris (Iris nigricans Dinsm.) following treatment with plant growth regulators

The effects of application method and concentration of gibberellic acid (GA₃), paclobutrazol and chlormequat on black iris performance were assessed. Plants (10 cm high, 4 ± 1 leaves) were sprayed with 125, 250, 375 or 500 mg L⁻¹ or drenched with 0.25, 0.5, 1 or 2 mg L⁻¹ GA₃. In a second experiment, the plants were sprayed with 100, 250, 500 or 1000 mg L⁻¹ or drenched with 0.25, 0.5, 1 or 2 mg L⁻¹ paclobutrazol. Other plants were sprayed with 250, 500, 1000 or 1500 mg L⁻¹ or drenched with 100, 250, 375 or 550 mg L⁻¹ chlormequat. In each experiment, the control treatment consisted of untreated plants. Results indicated that the tallest plants (37.3 cm) in the GA₃ experiment were those sprayed with 250 mg L⁻¹. The most rapid flowering (160 days after planting) occurred when a 375 mg L⁻¹ GA₃ spray was used, whereas flowering was delayed to 200 days using 1 mg L⁻¹ GA₃ drench. Drenching with 1 mg L⁻¹ GA₃ increased height of the flower stalk by 7 cm compared to the control. Though relatively slow to flower, plants drenched with 1 mg L⁻¹ GA₃ had long and rigid stalks, which were suitable as cut flowers. Number and characteristics of the sprouts were not affected by GA₃. All paclobutrazol sprays resulted in leaf falcation. A 500 or 1000 mg L⁻¹ paclobutrazol spray resulted in severe and undesirable control of plant height, drastic reduction in stalk height and weight, and delayed flowering. Plants drenched with 0.25 or 1 mg L⁻¹ paclobutrazol were suitable as pot plants. Chlormequat reduced plant height only at the highest drench concentration, which also reduced flowering to 70%. No leaf falcation was observed with GA₃ or chlormequat. Chemical names: ( ± )-(R*,R*)-beta-((4-chlorophenyl)methyl)-alpha-(1,1,-dimethylethyl)-1H-1,2,4,-triazol-1-ethanol (paclobutrazol); (2-chloroethyl) trimethylammonium chloride (chlormequat).     

Parental chromosome differentiation in citrangequat [Fortunella sp. × (Citrus sinensis × Poncirus trifoliata)] using CMA banding patterns

The efficiency of chromomycin A₃ (CMA) staining was examined for parental chromosome differentiation in citrange [Citrus sinensis (L.) Osbeck × Poncirus trifoliata (L.) Raf.] and citrangequat (Fortunella sp. × citrange). All of the accessions analyzed had the same chromosome number of 2n = 18. CMA staining revealed six characteristic banding patterns on the basis of the number and position of CMA positive bands (CMA⁺) as follows; A: two terminal and one proximal band, B: one terminal and one proximal band, C: two terminal bands, D: one terminal band, E: no band, and F: one proximal band. Chromosome CMA banding patterns of the accessions were 1A + 1B + 2C + 13D + 1F in Fortunella margarita, 2B + 2C + 7D + 7E in ‘Fukuhara’ orange, 2B + 10D + 6E in Poncirus trifoliata, 1B + 1C + 10D + 6E in citrange and 1A + 1C + 11D + 4E + 1F in citrangequat. The results of this study confirmed the intergeneric and tri-generic hybridity of citrange and citrangequat, respectively.     

Higher than optimum temperature under CO2 enrichment influences stomata anatomical characters in rose (Rosa hybrida)

There is little available information on the effects of temperature and CO₂ enrichment on stomata anatomical characteristics of plants. Effect of these two microclimates was studied on five rose (Rosa spp.) cultivars, viz. ‘First Red’ (used as check), ‘Arjun’, ‘Raktima’, ‘Raktagandha’ and ‘Pusa Pitamber’. Budded, single-stemmed rose cultivars having five lateral buds were grown in controlled environment growth cabinets under enriched CO₂ (1000 μmol mol⁻¹) and optimum (28/18 °C, T₀) or high (35/25 °C, T₁) temperature for 50 days. All observations were made on the abaxial leaf surface. Significant increases in stomatal density (68.7%), index (29.6%) and epidermal cell density (37.3%) were recorded in plants grown at high temperature over control with CO₂ enrichment. The cultivars responded differently in terms of length and width of guard cell and stoma (pore) under high temperature, however, the values averaged over treatments showed a significant reduction in these parameters. Further, number of stomata per leaf was higher (28.3%) in plants grown at high temperature, except First Red. A reduction in mean leaf area (26.7%) and dry mass (32.0%) was recorded at high rather than optimum temperature. The specific leaf area was maximum in Arjun (87%) while in First Red, a 14% reduction was noted at high temperature.     

Defence responses in leaves of resistant and susceptible pepper (Capsicum annuum L.) cultivars infected with different inoculum concentrations of Phytophthora capsici Leon

Three pepper cultivars (PM-702: resistant, Demre-8 and KM-hot: susceptible) with different resistances to Phytophthora capsici-22 (P. capsici-22) were inoculated with different concentrations of zoospores to analyze the time course of phenylalanine ammonia lyase (PAL) activity, malondialdehyde (MDA), hydrogen peroxide (H₂O₂), proline and total protein.     

Effect of elevated CO2 on vegetative and reproductive growth characteristics of the CAM plants Hylocereus undatus and Selenicereus megalanthus

This study examined the vegetative and reproductive growth responses of the crassulacean acid metabolism (CAM) vine-cactus fruit crop species Hylocereus undatus and Selenicereus megalanthus to CO₂ enrichment (1000 μmol mol⁻¹ vs. control of 380 μmol mol⁻¹). H. undatus plants enriched with CO₂ demonstrated 52%, 22%, 18%, and 175% increases, relative to plants measured in ambient CO₂, in total daily net CO₂ uptake, shoot elongation, shoot dry mass, and number of reproductive buds, respectively. The responses of S. megalanthus plants exposed to elevated CO₂ were greater than those of H. undatus under the same conditions. Compared to plant responses in ambient CO₂, under conditions of CO₂ enrichment, S. megalanthus showed 129%, 73%, 68%, and 233% increases in total daily net CO₂ uptake, shoot elongation, shoot dry mass, and number of reproductive buds, respectively. Moreover, for H. undatus, there was no significant change in fruit fresh mass although it showed a slight (7%) upward trend. On the other hand, fruit fresh mass of S. megalanthus significantly increased by 63% in response to elevated CO₂. These results indicate the high potential of CAM plants to respond to CO₂ enrichment. It is thus apparent that S. megalanthus grown under CO₂ enrichment may benefit from elevated CO₂ to a greater extent than H. undatus grown under sub-optimal growth conditions.     

Does root-sourced ABA play a role for regulation of stomata under drought in quinoa (Chenopodium quinoa Willd.)

The Andean seed crop quinoa (Chenopodium quinoa Willd.) is traditionally grown under drought and other adverse conditions that constrain crop production in the Andes, and it is regarded as having considerable tolerance to soil drying. The objective of this research was to study how chemical and hydraulic signalling from the root system controlled gas exchange in a drying soil in quinoa. It was observed that during soil drying, relative g_s and photosynthesis A_max (drought stressed/fully watered plants) equalled 1, until the fraction of transpirable soil water (FTSW) decreased to 0.82 ± 0.152 and 0.33 ± 0.061, respectively, at bud formation, indicating that photosynthesis was maintained after stomata closure. The relationship between relative g_s and relative A_max at bud formation was represented by a logarithmic function (r² = 0.79), which resulted in a photosynthetic water use efficiency WUE_Amax_/gs$\text{WU}{\text{E}}_{A_{\text{max}}/g_{\text{s}}}$ of 1 when FTSW > 0.8, and increased by 50% with soil drying to FTSW 0.7–0.4. Mild soil drying slightly increased ABA in the xylem. It is concluded that during soil drying, quinoa plants have a sensitive stomatal closure, by which the plants are able to maintain leaf water potential (ψ_l) and A_max, resulting in an increase of WUE. Root originated ABA plays a role in stomata performance during soil drying. ABA regulation seems to be one of the mechanisms utilised by quinoa when facing drought inducing decrease of turgor of stomata guard cells.     

Cold tolerance and short day acclimation in perennial Gaura coccinea and G. drummondii

The use of related species to integrate important traits into cultivated crops is a common practice in plant breeding. Gaura coccinea and, potentially its derived species Gaura drummondii, could be donor species for introgressing cold tolerance into non-hardy G. lindheimeri. However, cold tolerance and acclimation has not been studied in these species, so protocols for determining these traits are required. The objectives of this study were to determine the relative cold tolerance of G. coccinea, G. drummondii and whether short day photoperiod is involved in cold acclimation. G. drummondii from Texas, USA and G. coccinea from Minnesota and Texas, USA were subjected to freezing tests using whole plant or electrolyte leakage after natural acclimation or non-acclimation conditions. Minnesota genotypes were able to withstand colder temperatures (−12 °C) than Texas genotypes (−9 °C). Acclimation capacity was determined for whole plant and electrolyte leakage assays using three different plant organs—stem, crown, and rhizome. Underground rhizomes were the best predictors of cold tolerance, however they were difficult to obtain. Stem sections of G. drummondii (Texas) and G. coccinea (Minnesota and Texas) were used to determine a shift in acclimation under short days. The Minnesota G. coccinea genotypes demonstrated greater cold tolerance after 3 weeks of short days while Texas G. coccinea, G. drummondii genotypes did not change even after 5 weeks.     

Droplet-vitrification of apical shoot tips of Rubus fruticosus L. and Prunus cerasifera Ehrh.

Apical shoot tips excised from in vitro plantlets of blackberry (Rubus fruticosus L. ‘?a?anska Bestrna’) and cherry plum (Prunus cerasifera Ehrh.) were tested for recovery after cryopreservation using the droplet-vitrification technique. Following treatment for 30 min with a loading solution comprising 1.9 M glycerol and 0.5 M sucrose, explants were dehydrated with a highly concentrated cryoprotectant solution, so called vitrification solution. Shoot tips were dehydrated for 10, 20 and 30 min at room temperature with a solution derived from the original PVS2 solution (containing 37.5% (w/v) glycerol, 15% (w/v) dimethylsulfoxide, 15% (w/v) ethylene glycol and 22.5% (w/v) sucrose) and for 60, 90 and 120 min using the PVS3 solution (containing 50% (w/v) glycerol and 50% (w/v) sucrose). Explants were cooled by direct immersion in LN in 10 μl droplets of vitrification solution placed on aluminium foil strips. Rewarming was done by direct plunging of foil strips in a preheated (37 °C) unloading solution (0.8 M sucrose) for 30 s, after which an equal volume of unloading solution (at room temperature) was added for further incubation for 30 min. As for regrowth of blackberry, PVS3 proved more effective than the modified PVS2, but the difference was significant (P < 0.05) only for the shortest treatment duration. The duration of PVS3 treatment had no significant effect on regrowth of cryopreserved shoot tips (45.8–70%). By contrast, a 30-min treatment with modified PVS2 solution resulted in a significant increase in regeneration percentage (30%), as compared with a 10-min treatment with the same solution (5%). Cherry plum shoot tips were very sensitive to both vitrification solutions and growth recovery of cryopreserved samples was generally lower (5–20%) than that of blackberry explants. No significant influence of PVS treatment (both type of solution and treatment duration) on regrowth of cryopreserved shoot tips was observed with cherry plum shoot tips. Experiments performed in France and in Serbia produced similar results, thereby showing the robustness and reproducibility of the protocols developed.