Genotypic variation in salinity tolerance and its association with nodulation and nitrogen uptake in soybean

Saline soils hamper various physiological functions in soybean [Glycine max (L.) Merr.]. One example is the reduction in nitrogen (N) uptake capacity, a major dysfunction that limits soybean growth and yield under saline conditions. Previous studies have revealed that tolerance to salinity varies with cultivar; however, the cultivars used in these studies were selected solely based on agro-morphological traits. In this study, we examined genotypic variation in salinity tolerance among 85 soybean genotypes which were selected based on an assessment of both single nucleotide polymorphisms (SNP) markers and agro-morphological traits. Additionally, we examined whether salt tolerance is associated with nodulation and N uptake. We used a subset of the world soybean mini-core collection (80 cultivars) and an additional five cultivars/genetic lines (NILs72-T, NILs72-S, Enrei, En-b0-1, and En1282). All plants were grown in pots and treated with saline (final concentration of 150 mM NaCl) during the vegetative growth stage. To evaluate salinity tolerance, we used the ratio of saline-treated (S) to control (C) plant total dry weight [DW (S/C)]. The ratio differed markedly according to genotype. Furthermore, salinity-tolerant genotypes exhibited superior nodulation, leaf greenness, and N uptake under saline conditions. These results indicate that there is a marked genotypic variation in salinity tolerance, and that the tolerant genotypes exhibit greater nodulation and N uptake, although further studies are needed to clarify whether the superior nodulation and N uptake of salinity-tolerant genotypes are responsible for the observed tolerance.     

Field responses of grain sorghum to a salinity gradient

Grain sorghum is a potential crop for moderately saline areas, having been identified as fairly tolerant to salinity, and shown to contain intraspecific variability for that trait. The aim of this work was to describe the responses of grain sorghum to saline irrigation, assess the responses of a set of genotypes to salinity, and to analyze the relationships between several agronomic and physiological traits and salinity tolerance. In an experiment during three years, eleven public inbred lines and one cultivar were exposed to a salinity gradient (NaCl and CaCl₂, 1:1 w/w) created with a triple line source sprinkler system. The traits most affected by salinity were grain yield, number of grains per head, shoot dry weight (both grain and stover), harvest index, and leaf chloride, sodium, calcium, and potassium concentrations.Plant height, head length, and head number per plot were moderately affected by salinity, whereas flowering time, and total number of leaves per plant were unaffected. Two sets of three genotypes were identified with consistently contrasting responses to salinity across the three years. The differences in tolerance between these two groups were not associated with differences in total shoot biomass, but rather with different patterns of biomass partitioning under the most saline conditions. There were significant differences between the tolerant and susceptible genotypes in leaf chloride and potassium concentrations. The possible implications of the latter in the determination of the contrasting genotypic responses to salinity are discussed.     

18份大豆品种耐盐碱性筛选与综合鉴定

采用水培方法,用60 mmol·L^-1混合盐(NaHCO_3∶Na_2CO_3的摩尔比为9∶1)溶液,对18份大豆品种的幼苗进行盐碱胁迫。处理7 d后,测定株高、茎粗、叶面积、主根长、地上干重、净光合速率(Pn)、胞间CO_2浓度(Ci)、蒸腾速率(Tr)和气孔导度(Gs)等指标,通过主成分分析法和模糊数学隶属函数法对18份大豆品种进行耐盐碱性综合评价,并进行聚类分析,筛选出相对耐盐碱的大豆品种,从而为盐碱地大豆品种的应用提供理论依据。结果表明:经主成分分析,株高、主根长和净光合速率(Pn)的负荷量最大,可作为衡量大豆耐盐碱性与品种筛选的主要指标。不同品种大豆材料经过模糊数学隶属函数法进行耐盐碱性排序,品种间耐盐碱性表现出明显差异,最后通过聚类分析,18份大豆品种可以被分为三大类,其中杂交豆5号等4个品种为耐盐碱品种,吉育611和吉育299等11个品种为中等耐盐碱品种,吉育256和东农63为盐碱敏感品种。     

Assessing tolerance to soybean rust in selected genotypes

Breeding for tolerance to soybean rust is potentially one of the solutions to combating soybean rust; however, very little progress in tolerance breeding has been documented. Fourteen pre-selected genotypes were evaluated in a sprayed versus unsprayed split-plot trial conducted over three seasons for their tolerance to soybean rust. Different assessments of tolerance were compared for their effectiveness in discriminating between genotypes. Conventional methodology using a yield loss % index for assessing tolerance produced results which were poorly correlated with each other over seasons, which likely accounts for the historic lack of breeding success. This study has used the superiority measure (P_i) of Lin and Binns and the ecovalence statistic (W_i) of Wricke in a biplot to identify the most tolerant genotypes. A novel statistic (W_iP_i) has been generated from this biplot which facilitates the simultaneous selection for general performance and yield stability of genotypes under a range of rust stress conditions.     

Intracellular position of mitochondria and chloroplasts in bundle sheath and mesophyll cells of C3 grasses in relation to photorespiratory CO2 loss

In C₃ plants, photosynthetic efficiency is reduced by photorespiration. A part of CO₂ fixed during photosynthesis in chloroplasts is lost from mitochondria during photorespiration by decarboxylation of glycine by glycine decarboxylase (GDC). Thus, the intracellular position of mitochondria in photosynthetic cells is critical to the rate of photorespiratory CO₂ loss. We investigated the intracellular position of mitochondria in parenchyma sheath (PS) and mesophyll cells of 10 C₃ grasses from 3 subfamilies (Ehrhartoideae, Panicoideae, and Pooideae) by immunostaining for GDC and light and electron microscopic observation. Immunostaining suggested that many mitochondria were located in the inner half of PS cells and on the vacuole side of chloroplasts in mesophyll cells. Organelle quantification showed that 62–75% of PS mitochondria were located in the inner half of cells, and 62–78% of PS chloroplasts were in the outer half. In mesophyll cells, 61–92% of mitochondria were positioned on the vacuole side of chloroplasts and stromules. In PS cells, such location would reduce the loss of photorespiratory CO₂ by lengthening the path of CO₂ diffusion and allow more efficient fixation of CO₂ from intercellular spaces. In mesophyll cells, it would facilitate scavenging by chloroplasts of photorespiratory CO₂ released from mitochondria. Our data suggest that the PS cells of C₃ grasses have already acquired an initial structure leading to proto-Kranz and further C₃–C₄ intermediate anatomy. We also found that in the Pooideae, organelle positioning in PS cells on the phloem side resembles that in mesophyll cells.     

Effect of CO2 Concentration,Temperature and N Fertilization on Biomass Production of Soybean Genotypes Differing in N Fixation Capacity

Abstract

We tested the hypothesis that elevated CO₂ concentration [CO₂]-induced enhancement of biomass production of soybean is greater in a genotype that has a higher nitrogen (N) fixation capacity. Furthermore, we analyzed theinteractive effects of N fertilization, temperature and [CO₂] on biomass production. Three genetically related genotypes: Enrei (normally-nodulating genotype), Kanto 100 (supernodulating genotype), and En1282 (non-nodulating genotype) were grown in pots, with or without N fertilizer for two years (2004, 2005). They were then subjected to two different [CO₂] (ambient and elevated (ambient + 200 ?mol mol-¹)) × two temperature regimes (low,high (low + 4~5ºC)). Top dry weight at maturity was the greatest in the elevated [CO₂] × high temperature regime, irrespective of genotype and N fertilization. The [CO₂] elevation generally enhanced N acquisition and dry matter production during the vegetative growth stage, and the enhancement was more pronounced in the nodulating genotypes (Enrei and Kanto 100) than in the non-nodulating genotype (En1282), indicating that N supply through N fixation contributes to elevated [CO₂]-induced biomass production in soybean. However, the relative responsiveness ofbiomass production to elevated [CO₂] was not necessarily higher in the supernodulating genotype than the normally-nodulating genotype. The N utilization efficiency to produce biomass was inferior in the supernodulating genotype than in the normally-nodulating and non-nodulating genotypes. These results did not fully verify the hypothesis that elevated [CO₂]-induced enhancement of biomass production of soybean is greater in a genotype with a higher N fixation capacity.     

Evaluation of salt-tolerant genotypes of durum wheat derived from in vitro and field experiments

The performance of selected salt-tolerant genotypes of durum wheat [Triticum turgidum L. subsp. durum (Desf.) Husn.], derived from field and in vitro assessment methods, was evaluated under greenhouse and field conditions. Eight durum wheat genotypes comprising three salt-tolerant genotypes and one salt-sensitive genotype selected from each of the methods were used. This study was conducted under both saline and non-saline field conditions as well as under greenhouse condition with salinized solution culture at 0 mM (control), 75 and 150 mM NaCl (concentrations) using supplemental Ca²⁺. Days to heading, days to maturity, plant height, number of grains per spike, grain weight per spike, 1000 grain weight, number of spikes per m², grain yield and harvest index were recorded in the field experiments. Plant dry weight, Na⁺, K⁺ and Ca²⁺ accumulated in the hydroponically grown seedlings were measured 20 days after salinity treatments. In spite of the smaller range of genotypes used by the in vitro screening method, tolerant genotypes screened by the in vitro method (ITGs) performed comparably with those of the field-derived tolerant genotypes (FTGs) for grain yield under saline field conditions. Field salinity significantly reduced (P < 0.01) means of all traits averaged on eight tested genotypes. In vitro salt-tolerant genotypes Dipper-6 and Prion-1 produced the highest dry weight and K⁺/Na⁺ ratio under salt stress conditions (150 mM NaCl) in the greenhouse. Although dry matter correlated with the grain yield (R² = 0.37), the regression coefficient was higher for shoot K⁺/Na⁺ ratio (R² = 0.44). Dipper-6 (ITG) and Prion-1 (ITG) genotypes have been ranked superior while Massara-1 (ISG) was inferior for salt tolerance in the regression analysis. However, based on grain yield reduction Ajaia/Hora/Jro/3/Gan (FTG) and PI40100 (ITG) were the most tolerant having 58% and 60% reduction, respectively.     

Effects of saline and alkaline stresses in varying temperature regimes on seed germination of Leymus chinensis from the Songnen Grassland of China

Leymus chinensis is a dominant and most promising grass species in the Songnen Grassland of Northern China. Experiments were conducted to determine the effect of temperature, salinity, alkalinity and their interactions on seed germination. Seeds were germinated at four alternating temperatures (10–20, 15–25, 20–30 and 25–35°C), with saline stress (9:1 molar ratio of NaCl:Na₂SO₄) and alkaline stress (9:1 molar ratio of Na₂CO₃:NaHCO₃). Germination percentage and rate were inhibited by either an increase or decrease in temperature from the optimal temperature range of 20–30°C, and were also inhibited by an increase in salinity and alkalinity at all temperatures. The inhibitory effects of high salinity on germination were greater at 25–35°C, but seeds were subjected to more stress even though the alkalinity was low under this temperature. Recovery percentage was highest at 400 mm salinity at 20–30°C, but only at 100 mm alkalinity, and 25–35°C also resulted in lower recovery percentage under both stresses. Results suggest that saline stress and alkaline stress have different impacts on seed germination and that saline‐alkaline tolerance of L. chinensis seeds is affected by the interactions of temperature and salinity‐alkalinity. Early July sowing in the field is recommended when temperature is optimal and salinity‐alkalinity concentrations are reduced by the high rainfall.     

Effects of Soil Salinity and Alkalinity on Grain Quality of Tolerant,Semi-Tolerant and Sensitive Rice Genotypes

Soil salinity and alkalinity adversely affects the productivity and grain quality of rice.The grain quality of 19 rice genotypes characterized as salt tolerant (T),semi-tolerant (ST) and sensitive (S) was assessed in lysimeters containing saline and highly alkaline soils.Head rice recovery was reduced by salinity stress whereas it was not affected by alkalinity stress.The ratio of length to width (grain dimensions) was significantly reduced in the T genotype even at low electrical conductivity (EC,4 mS/cm) and alkalinity (pH 9.5),whereas in the ST genotype,it was significantly reduced at high salinity (EC 8 mS/cm).There was no significant effect of any levels of salinity or alkalinity on grain dimensions in the S genotype.Amylose content was significantly reduced in T and ST groups even at low EC (4 mS/cm) and alkalinity (pH 9.5) and the effect in the S genotype was only at high salinity.Starch content showed significant reduction at high salinity and alkalinity (EC 8 mS/cm and pH 9.8) in the T and ST genotypes and no significant effect was observed in the S genotype.The effect of both levels of salinity (EC 4 and 8 mS/cm) and high alkalinity (pH 9.8) on gel consistency was observed only in the S genotype.The tolerant genotypes IR36 under high salinity,and CSR10 and CSR11 under alkali stress showed less reduction in amylose content.The T genotype BR4-10,and ST genotypes CSR30,CSR29 and CSR13 showed better gel consistency under saline and alkali stress.Amylose content was affected even at low salinity stress and thus important to be considered in breeding rice for salt tolerance.Overall,the grain quality of T and ST genotypes was less affected by saline and alkali stress compared to S ones.     

Differential Sensitivity of Chloroplasts in Mesophyll and Bundle Sheath Cells in Maize,an NADP-Malic Enzyme-Type C4 Plant,to Salinity Stress

Abstract

The changes in chloroplast ultrastructure and the contents of chlorophyll, Na and K in response to salinity stress were investigated in leaves of maize, an NADP-malic enzyme-type C₄ plant species possessing dimorphic chloroplasts. The seedlings were treated with 0, 1, 2 or 3% NaCl for three or five days under a light or dark condition. In both light and dark conditions, the dry weight of salt-treated plants decreased as NaCl concentration increased. Chlorophyll and K contents of the second leaf blade decreased as NaCl concentration increased under the light condition but not under the dark condition. Na content of the second leaf blade was significantly higher at high NaCl concentrations under both light and dark conditions. However, Na content was much lower under the dark condition than light condition. Higher concentrations (2 and 3%) of NaCl significantly increased the size of plastoglobules, decreased the number and size of starch granules and altered the chloroplast ultrastructure. Under the light condition, mesophyll cell (MC) chloroplasts appeared more sensitive to the damaging effect of salinity than the bundle sheath cell (BSC) chloroplasts. MC chloroplasts became more globular in shape and showed swollen and disorganized thylakoids and reduced thickness of grana by salinity. BSC chloroplasts were less affected by salinity than MC chloroplasts. Although chloroplast size and number and size of starch granules were reduced, there was no structural distortion in the thylakoids of BSC chloroplasts. However, the thickness of grana was increased by salinity. Under the dark condition, the chloroplast structure was less affected by salinity. Though the envelope of BSC chloroplasts was occasionally damaged, the thylakoids in both MC and BSC chloroplasts were preserved under salinity stress. The present study suggests that the chloroplast damage caused by salinity is light-dependent and MC chloroplasts are more sensitive to salinity than BSC chloroplasts.     

干旱条件下土壤盐分对大豆生长及光合作用的影响

以盆栽大豆为材料,设置不同程度的土壤盐分(NaCl)、干旱及旱盐组合处理,然后测定各处理大豆植株的株高、生物量、光合作用指标以及植株的水分状况和Na~+、K~+含量,探索干旱条件下土壤盐分对大豆生长的影响及可能机制。结果表明:干旱和盐胁迫均可导致大豆叶片的净光合速率降低和生长量的减少,干旱还导致光合机构的严重损伤。但是,干旱和适量土壤盐分(100~150 mmol·L~(-1)NaCl)组合处理的大豆植株,其生长量、净光合速率和PSⅡ最大光化学效率都显著高于单一干旱处理。同时,旱盐组合处理的大豆叶片RWC、Na~+含量也高于单一干旱处理,水势和渗透势低于后者,且叶片Na~+含量与其渗透势降低显著相关。综合分析表明,在干旱条件下,土壤适量NaCl的存在使大豆能够吸收和积累更多Na~+等盐离子作为渗透调节物质,来降低渗透势、提高吸水能力,以改善植株的水分状况和光合性能,保持植株较高的生长速率,即土壤中适量盐分(NaCl)的存在可减轻干旱对大豆的负效应。     

The Role of Seed Structure and Oxygen Responsiveness in Pre-Germination Flooding Tolerance of Soybean Cultivars

Abstract

Flooding during germination often inhibits the germination and emergence of soybean [Glycine max (L.) Merr.], but little is known about the mechanisms involved in the tolerance of soybean cultivars to the damage caused by the flooding. The objectives of this study were to characterize the germination responses of soybean cultivars to pre-germination flooding and low oxygen conditions, and to identify possible seed traits responsible for the tolerance. A comparison of germination percentages among 18 cultivars under optimal and flooding conditions for 3 d enabled the identification of two tolerant cultivars (Williams and Peking), and two susceptible cultivars (Nakasennari and Enrei), which were used for further analyses. A comparison of the water absorption speed (WAS) in the following seed forms: embryo only (E), embryo with aleurone layer (E + AL), and intact seed with aleurone layer and seed coat (E + AL + SC) revealed that the aleurone layer provides a barrier to water penetration during the first hour of inundation regardless of cultivar. The intact seeds of a tolerant cultivar, Peking absorbed water more slowly than the other cultivars in the first hour of flooding. When the oxygen concentration in the seed container was reduced to 70 mL L-¹ for 3 d, the germination percentage of susceptible cultivars was reduced to approximately 70 % whereas that of tolerant cultivars remained high, indicating that responsiveness to low oxygen could also be responsible for pre-germination flooding tolerance of soybean cultivars.     

Correlation of Leaf Nitrogen,Chlorophyll and Rubisco Contents with Photosynthesis in a Supernodulating Soybean Genotype Sakukei 4

Abstract

Soybean requires more nitrogen (N) than gramineous crops because it accumulates a large amount of N in seeds, and its photosynthetic rate per leaf N is low. The supernodulating genotype Sakukei 4 has a superior symbiotic N₂ fixation capability, and thereby is potentially high-yielding. In our previous study, Sakukei 4 was characterized by having a superior ability to maintain high leaf N content and high photosynthetic rate. The objectives of this study were to know photosynthetic characteristics of Sakukei 4 in detail, especially, the responses to CO₂ concentration and light intensity, and to elucidate how the photosynthetic characteristics of Sakukei 4 are associated with the amounts of photosynthesis-related N compounds (chlorophyll and Rubisco). The three genotypes (Sakukei 4 - supernodulating cultivar derived from Enrei, Enrei - normally nodulating cultivar, En1282-non-nodulating line derived from Enrei) were grown at various N levels in this study. The CO₂ exchange rate (CER) in Sakukei 4 was higher than, or equal to that in Enrei at wide ranges of CO₂ concentrations (150-700 μmol mol-¹) and light intensities (200-1,500 μmol m-² s-¹ PPFD). Sakukei 4 had higher leaf N (N_l), chlorophyll (Chl_L) and Rubisco (Rub_L) contents per leaf area, but lower chlorophyll and Rubisco contents per leaf N content (Chl_L/N_l, Rub_L/N_l) than Enrei. The specific leaf weight (SLW) and leaf area trended to be lower in Sakukei 4 than in Enrei. These results indicate that the superior photosynthetic rate in Sakukei 4 is attributed to higher total N, chlorophyll and Rubisco contents per leaf area, but not to high rate of allocation of total N to these N compounds.     

The Effect of Elevated Atmospheric CO2 Concentration on Two Populus Clones Grown in a FACE System

SUMMARY

Two poplar clones, hybrid Populus deltoides Bartr. Ex Marsh X Populus nigra L. (Populus xeuramericana), clone I-214, and Populus deltoides, clone Lux, were grown from hardwood cuttings for one growing season in either ambient (360 μmol mol^?1) or elevated (560 μmol mol^?1) [CO₂] in FACE-systemrings at Rapolano Terme (Siena, Italy). Both clones I-214 and Lux exhibited a higher aboveground bio-mass, photosynthesis at light saturation and instantaneous transpiration efficiency (ITE) in CO₂-enriched air. The elevated [CO₂]-induced responses of clone I-214 included increased investment in branch and leaf biomass, and enhanced stem volume. The elevated [CO₂]-induced responses of clone Lux included an increase in the number of branches (and foliage area). Indication of photosynthetic acclimation under elevated [CO₂] was found during the early morning, but only in clone I-214. Stomatal conductance decreased under elevated [CO₂] particularly in clone Lux. Clone differences in response to elevated [CO₂] should be taken in account when planning future poplar plantations in forecast warmer and drier Mediterranean sites.     

Salt tolerance variability among stress‐selected Panicum coloratum cv. Klein plants

This work assessed intracultivar variability for salt tolerance within Panicum coloratum cv. Klein, explored some physiological parameters potentially associated with it and evaluated the contribution of cell division and expansion to the decreased leaf length observed under salinity. Individual plants that had survived severe stress environments in an established pasture were collected and clonal families were obtained by vegetative propagation. These were evaluated in a greenhouse, in pots with an inert substrate irrigated with nutrient solution containing 0, 200 or 400 mm NaCl. Salt tolerance was assessed from growth variables expressed as a percentage of non‐salinized controls. Changes induced by salinity in carbon fixation, soluble sugars and compatible solutes were also measured. The selected plants showed 33% higher salt tolerance than plants from the same cultivar obtained from seeds, and variability for salt tolerance was detected within the group, suggesting these plants could be valuable germplasm for breeding programmes for saline areas. All selected plants accumulated low leaf blade Na concentrations (< 0·1 mm  g^?1 dry weight on average), and K concentrations tended to remain high under salinity. A kinematic analysis indicated a reduction in the number of cells in the division‐only zone was the main cause of shorter leaves under stress. Although plants showed some differences in all these traits, they were not related to salt‐tolerance variability within this group of stress‐tolerant plants.     

Evaluation of the Effect of Photosynthesis on Biomass Production with Simultaneous Analysis of Growth and Continuous Monitoring of CO2 Exchange in the Whole Plants of Radish,cv Kosena under Ambient and Elevated CO2

Abstract

The effects of elevated CO₂ (approximate doubling of atmospheric CO₂ concentration) on the rate of photosynthesis estimated from continuous monitoring of CO₂ exchange in whole plants were investigated in radish cv. Kosena accompanied with simultaneous analysis of growth for 6 days from 15 to 21 days after planting (DAP). The elevated CO₂ increased the dry weights of hydroponically grown radish plants by 59% at 21 DAP.

The increase in dry weight was due to a combined effect of increased leaf area and increased photosynthetic rate per unit leaf area. Leaf area and the photosynthetic rate were increased by elevated CO₂ by 18-43% and 9-20%, respectively, during 15 to 21 DAP. Namely, an increase in the rate of photosynthesis is accompanied by an increase in leaf area, both having a significant effect on biomass production.     

Mechanism of High Photosynthetic Capacity in BC2F4 LinesDerived from a Cross between Oryza sativa and Wild Relatives O. rufipogon

Abstract

We found that several BC₂F₄ lines had high leaf photosynthetic rates under light-saturated and ambient CO₂ conditions. These lines are progenies of BC₂F₁ plants with high photosynthetic capacities which were generated by backcrossing between Oryza rufipogon (W630) and O. sativa cv. Nipponbare, as a recurrent parent. Some photosynthetic characteristics of the BC₂F₄ lines were investigated to identify the factors increasing photosynthetic rates. Photosynthetic rates of these lines under light-saturated conditions at 50 to 700 ppm CO₂ concentrations were higher than those in Nipponbare. The estimated-maximum photosynthetic rates under light-saturated and CO₂-saturated conditions in BC₂F₄ lines were also higher than that in Nipponbare. The photosynthetic rate under light-saturated and ambient CO₂ conditions was positively correlated with the carboxylation efficiency as an indicator of ribulose-1,5-bisphosphate carboxylase/oxygenase (Rubisco) activity in vivo rather than stomatal conductance. Initial and total Rubisco activities in vitro tended to be higher in the BC₂F₄ lines than in Nipponbare. The content of active Rubisco calculated from the activation state of Rubisco was also higher in the BC₂F₄ lines than in Nipponbare. These results suggest that high photosynthetic capacities of BC₂F₁ plants can be maintained high in their progenies and high photosynthetic rates under light-saturated and ambient CO₂ conditions in the BC₂F₄ lines are achieved mainly by the high activity of Rubisco due to the high active Rubisco content.     

Effects of water stress on photosynthesis and chlorophyll fluorescence of five potato cultivars

Summary Reduction of leaf photosynthesis due to water stress has been analyzed into various components and genetic variation in these components has been evaluated. Five potato cultivars were grown on nutrient solution in a conditioned glasshouse. Water stress was imposed by adding polyethylene glycol to the nutrient solution. Photosynthesis, transpiration and chlorophyll fluorescence were measured on intact leaves during the stress period and after recovery from the stress. Water stress reduced photosynthesis, initially as a consequence of stomatal closure, but after 3 days increasingly by inhibiting directly the photosynthetic capacity (mesophyll limitation). Stomatal closure correlated with the reduction in photosynthesis, but it was not the sole cause of this reduction because the internal CO₂ concentration in the leaves was not affected by water stress, indicative of inhibitory factors other than stomatal ones. Chlorophyll fluorescence emission suggested that the Calvin cycle was inhibited, while quantum efficiency was not affected at 17°C. Increasing the temperature to 27°C reduced quantum efficiency but only in the stress environment. The recovery of young leaves after relief of the stress was associated with a lower stomatal conductance but a higher mesophyll conductance compared with the control, which caused a low internal CO₂ concentration and probably invoked photo-inhibition and leaf damage. Cultivar differences in photosynthetic rate were highly significant under both optimal and stress conditions, and corresponded with differences in mesophyll conductance.     

Differences in the Vegetative Growth between Common and Tartary Buckwheat in Saline Hydroponic Culture

Abstract

Common buckwheat (Fagopyrum esculentum Moench cv. Tsushima) and Tartary buckwheat (F. tataricum (L.) Gaertn. cv. Pontivy) were grown in a nutrient solution with or without added NaCl to investigate interspecific differences in their responses to salinity, based on their dry-matter production. The mechanism of salt tolerance was also studied. Addition of 100 mM NaCl to the culture solution (salt treatment) lowered the plant growth rate to 48% and 16% of the control in Tsushima and Pontivy, respectively, and decreased the net assimilation rate and mean leaf area of Pontivy more severely than in Tsushima. The salt treatment decreased the leaf growth rate and leaf area per leaf to 30% and 72% of the control, respectively, in Tsushima, and to 12% and 52%, respectively, in Pontivy. It decreased the photosynthetic rate to 67% and 35% of the control, and stomatal conductance to 25% and 15% of the control in Tsushima and Pontivy, respectively. It also decreased the transpiration rate to 41% and 30% of the control in Tsushima and Pontivy, respectively, and increased the wateruse efficiency 1.6 times in Tsushima, but did not influence the wateruse efficiency in Pontivy. In the saline solution, the accumulation of Na⁺ in leaves and stem was greater in Pontivy than in Tsushima, but that in the roots, was greater in Tsushima than in Pontivy. In both species, Na⁺ accumulated rapidly in the leaves after removal of the roots in the saline solution. We conclude that the difference in salt tolerance between common and Tartary buckwheat may result from the difference in accumulation of Na⁺ in leaves and absorption of Na⁺ by the roots.     

Selection of Rice Genotypes for Salinity Tolerance Through Morpho-Biochemical Assessment

The present study reported the morpho-biochemical evaluation of 15 selected rice genotypes for salt tolerance at the seedling stage. Growth parameters including shoot length, root length, plant biomass, plant turgid weight, plant dry weight along with relative water content were measured after exposure to saline solution （with electrical conductivity value of 12 dS/m）. Genotypes, showing significant differential responses towards salinity in the fields, were assessed through 14 salinity-linked morpho-biochemical attributes, measured at 14 d after exposure of seedling in saline nutrient solution. Relative water content, chlorophyll a/b, peroxidase activity and plant biomass were identified as potential indicators of salt tolerance. Principal component analysis and successive Hierarchical clustering using Euclidean distance revealed that Talmugur, Gheus, Ghunsi, Langalmura, Sabitapalui, and Sholerpona were promising genotypes for further breeding programmes in rice. The maximum Euclidean distance was plotted between Thavallakanan and Talmugur （7.49）, followed by Thavallakanan and Langalmura （6.82）, indicating these combinations may be exploited as parental lines in hybridization programmes to develop salinity tolerant variety.