Genetic diversity and population structure of common bean (<Emphasis Type="Italic">Phaseolus vulgaris</Emphasis> L<Emphasis Type="Italic">.</Emphasis>) landraces from the East African highlands

The East African highlands are a region of important common bean production and high varietal diversity for the crop. The objective of this study was to uncover the diversity and population structure of 192 landraces from Ethiopia and Kenya together with four genepool control genotypes using morphological phenotyping and microsatellite marker genotyping. The germplasm represented different common bean production ecologies and seed types common in these countries. The landraces showed considerable diversity that corresponded well to the two recognized genepools (Andean and Mesoamerican) with little introgression between these groups. Mesoamerican genotypes were predominant in Ethiopia while Andean genotypes were predominant in Kenya. Within each country, landraces from different collection sites were clustered together indicating potential gene flow between regions within Kenya or within Ethiopia. Across countries, landraces from the same country of origin tended to cluster together indicating distinct germplasm at the national level and limited gene flow between the two countries highlighting divided social networks within the regions and a weak trans-national bean seed exchange especially for landrace varieties. One exception to this may be the case of small red-seeded beans where informal cross-border grain trade occurs. We also observed that genetic divergence was slightly higher for the Ethiopian landraces compared to Kenyan landraces and that Mesoamerican genotypes were more diverse than the Andean genotypes. Common beans in eastern Africa are often cultivated in marginal, risk-prone farming systems and the observed landrace diversity should provide valuable alleles for adaptation to stressful environments in future breeding programs in the region.     

Water Stress-Induced Responses in the Growth,Cuticular Wax Composition,Chloroplast Pigments and Soluble Protein Content,and Redox Metabolism of Two Genotypes of Ricinus communis L.

Journal of Plant Growth Regulation - The aim of this study was to investigate the physiological and biochemical responses to three different water regimes in two castor bean genotypes (BRS Energia...     

Aerenchyma development in different root zones of maize genotypes under water limitation and different phosphorus nutrition

Root cortical aerenchyma (RCA) is suggested to reduce metabolic cost for root growth, but it might lower water uptake by plants. The objective of this work was to evaluate the effects of drought and phosphorus on the RCA development along the root axis and to elucidate its role in water stress tolerance of two maize genotypes. Plants of drought-tolerant DKB390 and drought-sensitive BRS1010 genotypes were grown in Vermiculite at field capacity of 100, 75, 50, and 25 % and supplied with 0.1, 0.4, and 0.8 mM phosphorus. Growth parameters, RCA, and plant P content were evaluated for all plants. Higher RCA development was observed in DKB390 than in BRS1010. Drought reduced the percentage of RCA in the root-hair zone of both genotypes but increased its development in the root maturation zone. Phosphorus limitation enhanced RCA development only in the DKB390. Under drought stress, DKB390 showed resilient growth whereas growth was inhibited in BRS1010. Higher root P content was related to its higher supply. Therefore, RCA formation was induced either by drought or by phosphorus limitation, while no interaction was evident. The RCA development varied along the root axis in order to balance water and phosphorus uptake and the drought response was genotype dependent.     

Photosynthesis, photorespiration and productivity of wheat and soybean genotypes

The results of the numerous measurements obtained during the last 40 years on gas exchange rate, photosynthetic carbon metabolism by exposition in ¹⁴CO₂ and activities of primary carbon fixation enzyme, ribulose‐1,5‐bisphosphate carboxylase/oxygenase (RuBPC/O), in various wheat and soybean genotypes grown over a wide area in the field and contrasting in photosynthetic traits and productivity are presented in this article. It was established that high productive wheat genotypes (7–9 t ha^?1) with the optimal architectonics possess higher rate of CO₂ assimilation during the leaf ontogenesis. Along with the high rate of photosynthesis, high values of photorespiration are characteristic for the high productive genotypes. Genotypes with moderate (4–5 t ha^?1) and low (3 t ha^?1) grain yield are characterized by relatively low rates of both CO₂ assimilation and photorespiration. A value of photorespiration constitutes 28–35% of photosynthetic rate in contrasting genotypes. The activities of RuBPC and RuBPO were changing in a similar way in the course of the flag leaf and ear elements development. High productive genotypes are also characterized by a higher rate of biosynthesis and total value of glycine–serine and a higher photosynthetic rate. Therefore, contrary to conception arisen during many years on the wastefulness of photorespiration, taking into account the versatile investigations on different aspects of photorespiration, it was proved that photorespiration is one of the evolutionarily developed vital metabolic processes in plants and the attempts to reduce this process with the purpose of increasing the crop productivity are inconsistent.     

Interaction of Anthonomus grandis and cotton genotypes: biological and behavioral responses

The boll weevil, Anthonomus grandisBoheman (Coleoptera: Curculionidae), is a key pest of cotton, Gossypium hirsutumL. (Malvaceae). Knowledge about boll weevil feeding and oviposition behavior and its response to plant volatiles can underpin our understanding of host plant resistance, and contribute to improved monitoring and mass capture of this pest. Boll weevil oviposition preference and immature development in four cotton genotypes (CNPA TB90, TB85, TB15, and BRS Rubi) were investigated in the laboratory and greenhouse. Volatile organic compounds (VOCs) produced by TB90 and Rubi genotypes were obtained from herbivore‐damaged and undamaged control plants at two phenological stages – vegetative (prior to squaring) and reproductive (during squaring) – and four collection times – 24, 48, 72, and 96 h following herbivore damage. The boll weevil exhibited similar feeding and oviposition behavior across the four tested cotton genotypes. The chemical profiles of herbivore‐damaged plants of both genotypes across the two phenological stages were qualitatively similar, but differed in the amount of volatiles produced. Boll weevil response to VOC extracts was studied using a Y‐tube olfactometer. The boll weevil exhibited similar feeding and oviposition behavior at the four tested cotton genotypes, although delayed development and production of smaller adults was found when fed TB85. The chemical profile of herbivore‐damaged plants of both genotypes at the two phenological stages and time periods (24–96 h) was similar qualitatively, with 30 identified compounds, but differed in the amount of volatiles produced. Additionally, boll weevil olfactory response was positive to herbivory‐induced volatiles. The results help to understand the interaction between A. grandis and cotton plants, and why it is difficult to obtain cotton genotypes possessing constitutive resistance to this pest.     

Simultaneous gas exchange and fluorescence measurements indicate differences in the response of sunflower,bean and maize to water stress

Gas exchange and fluorescence measurements of attached leaves of water stressed bean, sunflower and maize plants were carried out at two light intensities (250 mol quanta m^-2s^-1 and 850 mol quanta m^-2s^-1). Besides the restriction of transpiration and CO₂ uptake, the dissipation of excess light energy was clearly reflected in the light and dark reactions of photosynthesis under stress conditions. Bean and maize plants preferentially use non-photochemical quenching for light energy dissipation. In sunflower plants, excess light energy gave rise to photochemical quenching. Autoradiography of leaves after photosynthesis in ¹⁴CO₂ demonstrated the occurrence of leaf patchiness in sunflower and maize but not in bean. The contribution of CO₂ recycling within the leaves to energy dissipation was investigated by studies in 2.5% oxygen to suppress photorespiration. The participation of different energy dissipating mechanisms to quanta comsumption on agriculturally relevant species is discussed.Abbreviations F_o minimal fluorescence - F_m maximal fluorescence - F_p peak fluorescence - g leaf conductance - P_N net CO₂ uptake - q_N coefficient of non-photochemical quenching - q_P coefficient of photochemical quenching     

Genetic diversity in Capsicum germplasm based on microsatellite and random amplified microsatellite polymorphism markers

A sound knowledge of the genetic diversity among germplasm is vital for strategic germplasm collection, maintenance, conservation and utilisation. Genomic simple sequence repeats (SSRs) and random amplified microsatellite polymorphism (RAMPO) markers were used to analyse diversity and relationships among 48 pepper (Capsicum spp.) genotypes originating from nine countries. These genotypes covered 4 species including 13 germplasm accessions, 30 improved lines of 4 domesticated species and 5 landraces derived from natural interspecific crosses. Out of 106 SSR markers, 25 polymorphic SSR markers (24 %) detected a total of 76 alleles (average, 3.04; range, 2–5). The average polymorphic information content (PIC) was 0.69 (range, 0.29–0.92). Seventeen RAMPO markers produced 87 polymorphic fragments with average PIC of 0.63 (range, 0.44–0.81). Dendrograms based on SSRs and RAMPOs generated two clusters. All 38 Capsicum annuum genotypes and an interspecific landrace clustered together, whereas nine non-annuum (three Capsicum frutescens, one Capsicum chinense, one Capsicum baccatum and four interspecific landraces) genotypes clustered separately. Genetic variation within non-annuum genotypes was greater than the C. annuum genotypes. Distinctness of interspecific derivative landraces grown in northeast India was validated; natural crossing between sympatric Capsicum species has been proposed as the mechanism of their origin.     

Hypersensitive response of beans to Apion godmani (Coleoptera: Curculionidae)

High levels of resistance to Apion godinani Wagner have been reported in bean, Phaseolus vulgaris L., landraces from Mexico. We report on the role of hypersensitivity to A. godmani in five resistant and three susceptible bean genotypes. In susceptible genotypes (cultivars 'Canario 107','Jamapa', and 'Zacatecas 45'), the eggs and first instars of A. godmani were embedded in the pod mesocarp and usually were surrounded by healthy tissue. In contrast, in resistant landraces ('Amarillo 154', 'Amarillo 155', 'J-117', 'Puebla 36', and 'Pinto 168'), necrotic tissues developed concentrically around the oviposition site, encapsulating eggs and dead larvae. An inverse relationship between percentage egg and larval encapsulation at the early immature pod stages and percentage of damaged seeds at harvest was found. Results indicate that hypersensitivity in developing pods plays an important role in antibiosis to A. godmani in beans. This information will facilitate future genetic and biochemical research and provide much needed information concerning the phenotypic basis of resistance to A. godmani in bean.     

根据光合作用能量代谢测定光呼吸的方法研究

本文根据光合作用和光呼吸途径能量代谢,通过改变外界CO2和O2浓度,计算卡尔文循环固定的CO2和光呼吸消耗的O2。结果表明,可以通过3种方法计算。方法1,测定在CO2饱和点（A）和正常CO2（A＇）浓度下吸收的CO2,得出光呼吸消耗的O2为：18／19（A-A＇）,卡尔文循环固定的CO2为：1／19（6A＋13A＇＋19Rd）。方法2,测定在不含O2的空气中（O）和正常O2（O’）浓度下释放的O2,得出光呼吸消耗的O2为：-13／5O-O＇-18／5Rd,卡尔文循环固定的CO2为：13／18（O＇—O）。方法3,测定在正常情况下吸收的CO2（A）和释放的O2（O＇）,得出光呼吸消耗的O2为：18（O＇—A＇）,卡尔文循环固定的CO2为：6O＇-5A＇＋Rd。测定在CO2饱和点和正常CO2浓度下吸收的CO2计算出水稻光呼吸释放的CO2占光合作用固定的24％-40％。     

Reactive Oxygen Species and Relative Enzyme Activities in the Development of Aerial Roots of Chinese Banyan (Ficus microcarpa)

Although previous research has indicated that reactive oxygen species (ROS) regulate cell extension and tissue ontogenesis, the functions of ROS in aerial roots have not been previously studied. This research evaluated ROS production and dissipation in aerial roots of Chinese banyan (Ficus microcarpa). Aerial root segments (4 cm long) were cut from trees and divided into developmental zones 1, 2, and 3 (0–5, 5–15, and 15–25 mm from root tip, respectively). According to histochemical and biochemical determinations, production of the superoxide radical (O ₂ ^·– ), hydrogen peroxide (H₂O₂), and the hydroxyl radical (^·OH) decreased from zone 1 to zone 3. The detected ROS increased with the application of exogenous stimulators of ROS generation and decreased with the application of exogenous inhibitors of ROS generation. Based on protein content, superoxide dismutase (SOD) activity increased but peroxidase (POD) and catalase (CAT) activities decreased from zone 1 to zone 3, whereas based on root segment fresh weight, SOD and CAT activities did not differ among the zones but POD activity decreased from zone 1 to 3. We conclude that ROS are generated mainly in the rapidly developing zones of aerial roots and suggest that NADPH oxidase, POD, and SOD control ROS generation. POD activity and the hydroxyl cycle seem particularly important in ROS generation in aerial roots.     

The influence of dietary lipid composition on liver mitochondria from mice following 1 month of calorie restriction

To investigate the role mitochondrial membrane lipids play in the actions of CR (calorie restriction), C57BL/6 mice were assigned to four groups (control and three 40% CR groups) and the CR groups were fed diets containing soya bean oil (also in the control diet), fish oil or lard. The fatty acid composition of the major mitochondrial phospholipid classes, proton leak and H₂O₂ production were measured in liver mitochondria following 1 month of CR. The results indicate that mitochondrial phospholipid fatty acids reflect the PUFA (polyunsaturated fatty acid) profile of the dietary lipid sources. CR significantly decreased the capacity of ROS (reactive oxygen species) production by Complex III but did not markedly alter proton leak and ETC (electron transport chain) enzyme activities. Within the CR regimens, the CR-fish group had decreased ROS production by both Complexes I and III, and increased proton leak when compared with the other CR groups. The CR-lard group showed the lowest proton leak compared with the other CR groups. The ETC enzyme activity measurements in the CR regimens showed that Complex I activity was decreased in both the CR-fish and CR-lard groups. Moreover, the CR-fish group also had lower Complex II activity compared with the other CR groups. These results indicate that dietary lipid composition does influence liver mitochondrial phospholipid composition, ROS production, proton leak and ETC enzyme activities in CR animals.     

Effects of nitrogen rates on grain yield and nitrogen agronomic efficiency of durum wheat genotypes under different environments

Durum wheat is an important staple food crop in Tunisia and other Mediterranean countries and is grown in various climatic conditions. Production and yield are however severely limited not only by drought events but also by reduced levels of nitrogen fertilisation. A study was carried out at two locations in the sub‐humid area of Tunisia: Mateur in 2009–10 and 2010–11 and Beja in 2011–12 and 2012–13 under rainfed conditions. Four durum wheat genotypes (landraces: Bidi, Azizi; improved: Om Rabia, Khiar) were evaluated for nitrogen agronomic efficiency and related agronomic traits under various nitrogen rates: 0, 50, 100, 150, 200 and 250 kg N ha^?1, with three replications. There was a significant interaction effect (P ≤ 0.001) environments × genotypes × N treatments for grain yield (GY), biomass yield (BY), harvest index (HI), partial factor productivity of applied nitrogen (PFP_N) and nitrogen agronomic use efficiencies (NAE). GY was the most affected trait by nitrogen applied showing an increase of 94% under high N treatment (250 kg N ha^?1) compared to control plots without N treatments. A significant linear regression exists between GY (0 N) and GY for the different N rates (r = 0.70; P < 0.001). This effect was more pronounced for improved genotypes than landraces for all parameters excepting BY and NAE_BY. BY showed +11% increase in landraces than improved genotypes. PFP_N showed an average decrease of 65% under high‐N fertilisation with 10% prevalence for improved genotypes. Landraces tend to promote vegetative growth while grain filling efficiency was higher for improved genotypes.     

Effects of Nitrate Level on Nitrogen Metabolism in Winged Bean and Soya Bean

The effects of high (15 mM) and low (0.75 mM) solution nitratelevels on nitrogen metabolism in three genotypes (IL 7A, IL13 and IL 21) of winged beans [Psophocarpus tetragonolobus (L.)DC.] and one genotype (Williams) of soya bean [Glycine max (L.)Merrill] were investigated. Plants were grown for 42 days ina greenhouse in solution culture prior to sampling. The 15 mM nitrate treatment resulted in greater growth of allplant parts except roots. Growth of soya beans was more responsiveto nitrate level than was growth of winged beans. The high nitratelevel inhibited nodulation in all plants. The IL 13 and IL 21winged bean genotypes had similar nitrogenase activity (acetylenereduction per plant) as the soya bean and IL 7A winged beangenotype had lower activity. However, the IL 13 winged beangenotype had higher nitrogenase activity (acetylene reductionper unit nodule mass) than the other three genotypes which allhad similar activity. The 15 mM solution nitrate level stimulatedleaf and root nitrate reductase (NR) activity for all plants.All winged bean genotypes had higher leaf NR activity and higherpercentage reduced- and nitrate-nitrogen contents of leavesand stems compared with soya beans. However, total protein (reducednitrogen) was greater in soya beans when sampled indicatingthat more nitrate had been metabolized by soya beans than bywinged beans during the 42-day growth period. Psophocarpus tetragonolobus (L.) DC., winged bean, Glycine max (L.) Merrill, Soya bean, nitrate reductase, nitrogen fixation, nitrogenase activity, nodulation     

Phytoremediation: green technology for the removal of mixed contaminants of a water supply reservoir

The Iraí Reservoir, a water supply in Brazil, is constantly impacted by anthropogenic activities such as waste inputs from agriculture, hospitals and urbanization, resulting toxic cyanobacterial blooms causing economic, social and environmental problems. This study assessed the concentration of some common contaminants of the Iraí Reservoir, namely paracetamol, diclofenac and microcystin-LR and tested whether a laboratory scale Green Liver System^® would serve as a suitable technology to remove these contaminants. Further, the study investigated whether the pollutants caused adverse effects to the macrophytes using catalase as a biomarker for oxidative stress and investigated whether biotransformation (glutathione S-transferase) was a main route for detoxification. Egeria densa, Ceratophyllum demersum and Myriophyllum aquaticum were exposed to a mixture of the three contaminants for 14?days in a concentration range similar to those detected in the reservoir. The plants removed 93% of diclofenac and 100% of MC-LR after 14?days. Paracetamol could not be detected. Catalase and glutathione S-transferase enzyme activities remained unaltered after the 14-day exposure, indicating that the mixture did not cause oxidative stress. The study showed that the aquatic macrophytes used are suitable tools to apply in a Green Liver System^® for the remediation of mixed pollutants.     

Chromium (VI)-induced hormesis and genotoxicity are mediated through oxidative stress in root cells of Allium cepa L.

Chromium (VI) genotoxicity was evaluated in Allium bioassay by using different treatment protocols. Treatment of bulbs of Allium cepa L. with Cr(VI) at a range of concentrations for 5 days (120 h) exhibited low dose (12.5 μM) stimulation and high dose (25–200 μM) inhibition of root growth apparently indicating hormesis. Inhibition of root growth was correlated with the dose-dependent increase in generation of reactive oxygen species (ROS), cell death, lipid peroxidation, repression of antioxidative enzymes (catalase, superoxide dismutase, ascorbate peroxidase), induction of DNA damage, chromosome aberrations or micronuclei in root cells. The above effects were, however, reversed when the duration of Cr(VI) treatment was limited to 3–24 h followed by recovery in tap water for 4 days that resulted in the dose-dependent stimulation of root growth, mitosis and increased activity of the antioxidative enzymes that obliterated oxidative stress and genotoxicity. The above Cr(VI)-induced stimulation of root growth was effectively countered by pre- or post-treatments of dimethylthiourea, a ROS-scavenger. These findings underscored that Cr(VI), depending on the magnitude of the dose (concentration × time), could either be stimulatory or inhibitory for root growth that underlined the crucial role of ROS having obvious implications in agriculture, post harvest technology and human health.     

Processes contributing to photoprotection of grapevine leaves illuminated at low temperature

Photoinactivation of photosystem II (PSII) and energy dissipation at low leaf temperatures were investigated in leaves of glasshouse-grown grapevine ( Vitis vinifera L. cv. Riesling). At low temperatures (< 15°C), photosynthetic rates of CO₂ assimilation were reduced. However, despite a significant increase in the amount of light excessive to that required by photosynthesis, grapevine leaves maintained high intrinsic quantum efficiencies of PSII ( F _v/ F _m) and were highly resistant to photoinactivation compared to other species. Non-photochemical energy dissipation involving xanthophylls and fast D1 repair were the main protective processes reducing the 'gross' rate of photoinactivation and the 'net' rate of photoinactivation, respectively. We developed an improved method of energy dissipation analysis that revealed up to 75% of absorbed light is dissipated thermally via pH- and xanthophyll-mediated non-photochemical quenching at low temperatures (5–15°C) and moderate (800 µmol quanta m⁻² s⁻¹) light. Up to 20% of the energy flux contributing to electron transport was dissipated via photorespiration when taking into account temperature-dependent mesophyll conductance; however, this flux used in photorespiration was only a relatively small amount of the total absorbed light energy. Photoreduction of O₂ at photosystem I (PSI) and subsequent superoxide detoxification (water-water cycle) was more sensitive to inhibition by low temperature than photorespiration. Therefore the water-water cycle represents a negligibly small energy sink below 15°C, irrespective of mesophyll conductance.     

Evaluation of mitochondrial redox status and energy metabolism of X-irradiated HeLa cells by LC/UV,LC/MS/MS and ESR

To evaluate the metabolic responses in tumour cells exposed to ionizing radiation, oxygen consumption rate (OCR), cellular lipid peroxidation, cellular energy status (intracellular nucleotide pool and ATP production), and mitochondrial reactive oxygen species (ROS), semiquinone (SQ), and iron–sulphur (Fe?S) cluster levels were evaluated in human cervical carcinoma HeLa cells at 12 and 24?h after X-irradiation. LC/MS/MS analysis showed that levels of 8-iso PGF_2α and 5-iPF_2α-VI, lipid peroxidation products of membrane arachidonic acids, were not altered significantly in X-irradiated cells, although mitochondrial ROS levels and OCR significantly increased in the cells at 24?h after irradiation. LC/UV analysis revealed that intracellular AMP, ADP, and ATP levels increased significantly after X-irradiation, but adenylate energy charge (adenylate energy charge (AEC)?=?[ATP?+?0.5?×?ADP]/[ATP?+?ADP?+?AMP]) remained unchanged after X-irradiation. In low-temperature electron spin resonance (ESR) spectra of HeLa cells, the presence of mitochondrial SQ at g?=?2.004 and Fe–S cluster at g?=?1.941 was observed and X-irradiation enhanced the signal intensity of SQ but not of the Fe–S cluster. Furthermore, this radiation-induced increase in SQ signal intensity disappeared on treatment with rotenone, which inhibits electron transfer from Fe–S cluster to SQ in complex I. From these results, it was suggested that an increase in OCR and imbalance in SQ and Fe–S cluster levels, which play a critical role in the mitochondrial electron transport chain (ETC), occur after X-irradiation, resulting in an increase in ATP production and ROS leakage from the activated mitochondrial ETC.     

Phosphorus runoff from a phosphorus deficient soil under common bean (Phaseolus vulgaris L.) and soybean (Glycine max L.) genotypes with contrasting root architecture

The selection and breeding of crop genotypes with root traits that improve soil resource extraction is a promising avenue to improved nutrient and water use efficiency in low-input farming systems. Such genotypes may accelerate nutrient extraction (“nutrient mining”), but may also reduce nutrient loss via soil erosion by producing greater shoot biomass and by direct effects of root traits on aggregate formation and water infiltration. Little is known about the effects of root architecture on phosphorus (P) runoff and soil erosion, and the relative importance of root and shoot traits on runoff P loss has not been determined. Four genotypes of common bean (Phaseolus vulgaris L.) and two genotypes of soybean (Glycine max) selected for contrasting root architecture were grown in a low P soil (Aquic Fragiudult, <20 mg kg^?1 Mehlich-3 P, 3% slope) and subjected to rainfall-runoff experiments with and without shoot removal. Plots with intact shoots had significantly lower runoff volumes (1.3–7.6 mm) and total P loads in runoff (0.005–0.32 kg ha^?1) than plots with shoots removed (7.0–16.8 mm; 0.025–1.95 kg ha^?1). Dissolved reactive P leached from plant material did not contribute significantly to P loss in runoff. Total root length acquired from soil cores differed significantly among genotypes. Root length densities in the upper 15 cm of soil mid-way between rows were less than 4.0 cm cm^?3 and variation in root length density was not correlated with runoff or P loss. Root length density also did not affect rainfall infiltration or surface runoff volume. We conclude that for annual dicotyledonous crops such as bean and soybean with relatively low root length densities, root traits have little direct effect on soil erosion.     

Calcium chloride enhances the antioxidative system of sweet potato (Ipomoea batatas) under flooding stress

Three sweet potato varieties, Taoyuan 2, Simon 1 and Sushu 18, were pretreated with four levels of CaCl₂ (0, 60, 120 and 180 kg ha^?1) weekly for 50 days from planting before being subjected to non‐flooding (control) and flooding conditions. The experiment used a randomised complete block design with a split‐split plot arrangement of treatments. Young, fully expanded leaves from each plant were clipped for measuring enzyme activities and antioxidant contents. The three genotypes exhibited unique abilities and specificities through the antioxidative systems in response to flooding stress. The level of activity of the antioxidative system in sweet potato leaves was related to CaCl₂ pretreatment during flooding. The ascorbate peroxidase, superoxide dismutase, glutathione reductase, reduced ascorbate, total ascorbate, reduced glutathione and malondialdehyde contents of the three sweet potato varieties under flooding stress significantly increased because of pretreatment with 60 and 120 kg ha^?1 of CaCl₂. Moreover, pretreatment with 60 and 120 kg ha^?1 CaCl₂ enhanced the flooding tolerance of all three sweet potato varieties and mitigated the effects of flooding stress. However, pretreatment with 180 kg ha^?1 CaCl₂ markedly decreased some enzyme activities and antioxidant contents under a flooded condition. Calcium most likely played a role in the antioxidative system in the leaves of these three sweet potato varieties under flooding stress, as an optimum amount strengthened their oxidative systems.