Identification of pearl millet [Pennisetum glaucum (L.) R. Br.] lines tolerant to soil salinity

Crop tolerance to salinity is of high importance due to the extent and the constant increase in salt-affected areas in arid and semi-arid regions. Pearl millet (Pennistum glaucum), generally considered as fairly tolerant to salinity, could be an alternative crop option for salt affected areas. To explore the genotypic variability of vegetative-stage salinity tolerance, 100 pearl millet lines from ICRISAT breeding programs were first screened in a pot culture containing Alfisol with 250 mM NaCl solution as basal application. Subsequently, 31 lines including many parents of commercial hybrids, selected from the first trial were re-tested for confirmation of the initial salinity responses. Substantial variation for salinity tolerance was found on the basis of shoot biomass ratio (shoot biomass under salinity/ non-saline control) and 22 lines with a wide range of tolerance varying from highly tolerant to sensitive entries were identified. The performance of the genotypes was largely consistent across experiments. In a separate seed germination and seedling growth study, the seed germination was found to be adversely affected (more than 70% decrease) in more than half of the genotypes with 250 mM concentration of NaCl. The root growth ratio (root growth under salinity/control) as well as shoot growth ratio was measured at 6 DAS and this did not reflect the whole plant performance at 39 DAS. In general, the whole plant salinity tolerance was associated with reduced shoot N content, increased K⁺ and Na⁺ contents. The K⁺/Na⁺ and Ca⁺⁺/Na⁺ ratios were also positively related to the tolerance but not as closely as the Na⁺ content. Therefore, it is concluded that a large scope exists for improving salt tolerance in pearl millet and that shoot Na⁺ concentration could be considered as a potential non-destructive selection criterion for vegetative-stage screening. The usefulness of this criterion for salinity response with respect to grain and stover yield remains to be investigated.     

Using Growth and Ionic Contents of Wheat Seedlings as Rapid Screening Tool for Salt Tolerance

High germination percentage with vigorous early growth is preferred for harvesting good wheat stand under saline soils. Therefore, an attempt for rapid screening of wheat genotypes for salt tolerance was made in this study. Eleven wheat genotypes including salt tolerant check Kiran-95were subjected to salinity (120 and 160 mMNaCl) along with non-saline control. Results showed a gradual decrease in seed germination and restricted seedling growth in tested wheat genotypes in response to increasing NaCl concentration in nutrient solution. Among the genotypes, NIA-AS-14-6 and NIA-AS-14-7 exhibited more sensitivity towards the salt stress at the germination stage but NIA-AS-14-6 performed quite satisfactorily later on at the seedling stage. Wheat genotypes NIA-AS-14-2, NIA-AS-14-4, NIA-AS-14-5, NIA-AS-14-10, and Kiran-95 showed better performance in term of root-shoot length, plant biomasses (fresh and dry), K⁺:Na⁺ ratio with least Na⁺ content, and high accumulation of K⁺ at higher levels of NaCl stress. On the basis of overall results, the categorization of genotypes was carried out as sensitive, moderately tolerant, and tolerant. Wheat genotypes NIA-AS-14-2, NIA-AS-14-4, NIA-AS-14-5, NIA-AS-14-10, and Kiran-95 grouped as tolerant, moderately salt tolerant group comprised of NIA-AS-14-1, NIA-AS-14-3, NIA-AS-14-6, and NIA-AS-14-8, whereas, NIA-AS-14-7 and NIA-AS-14-9 were found sensitive to salt stress. Principal component analysis revealed that components I and II contributed 70 and 16.5%, respectively. All growth parameters are associated with each other except RDW. In addition to growth traits, low Na⁺ and improved K⁺ content with better K⁺:Na⁺ ratio may be used for screening of salt tolerance in wheat as potential physiological criteria.     

Identification and Characterization of Salt Tolerance of Wheat Germplasm Using a Multivariable Screening Approach

Salinity is one of the major limitations to wheat production worldwide. This study was designed to evaluate the level of genetic variation among 150 internationally derived wheat genotypes for salinity tolerance at germination, seedling and adult plant stages, with the aim of identifying new genetic resources with desirable adaptation characteristics for breeding programmes and further genetic studies. In all the growth stages, genotype and salt treatment effects were observed. Salt stress caused 33 %, 51 % and 82 % reductions in germination vigor, seedling shoot dry matter and seed grain yield, respectively. The rate of root and shoot water loss due to salt stress exhibited significant negative correlation with shoot K⁺, but not with shoot Na⁺ and shoot K⁺/Na⁺ ratio. The genotypes showed a wide spectrum of response to salt stress across the growth stages; however, four genotypes, Altay2000, 14IWWYTIR‐19 and UZ‐11CWA‐8 (tolerant) and Bobur (sensitive), exhibited consistent responses to salinity across the three growth stages. The tolerant genotypes possessed better ability to maintain stable osmotic potential, low Na⁺ accumulation, higher shoot K⁺ concentrations, higher rates of PSII activity, maximal photochemical efficiency and lower non‐photochemical quenching (NPQ), resulting in the significantly higher dry matter production observed under salt stress. The identified genotypes could be used as parents in breeding for new varieties with improved salt tolerance as well as in further genetic studies to uncover the genetic mechanisms governing salt stress response in wheat.     

Screening sorghum genotypes for salinity tolerant biomass production

Genetic improvement of salt tolerance is of high importance due to the extent and the constant increase in salt affected areas. Sorghum [Sorghum bicolor (L.) Moench] has been considered relatively more salt tolerant than maize and has the potential as a grain and fodder crop for salt affected areas. One hundred sorghum genotypes were screened for salinity tolerance in pots containing Alfisol and initially irrigated with a 250-mM NaCl solution in a randomized block design with three replications. Subsequently 46 selected genotypes were assessed in a second trial to confirm their responses to salinity. Substantial variation in shoot biomass ratio was identified among the genotypes. The performance of genotypes was consistent across experiments. Seven salinity tolerant and ten salinity sensitive genotypes are reported. Relative shoot lengths of seedlings were genetically correlated to the shoot biomass ratios at all stages of sampling though the relationships were not close enough to use the trait as a selection criterion. In general, the whole-plant tolerance to salinity resulted in reduced shoot Na⁺ concentration. The K⁺/Na⁺ and Ca²⁺/Na⁺ ratios were also positively related to tolerance but with a lesser r ². Therefore, it is concluded that genotypic diversity exists for salt tolerance biomass production and that Na⁺ exclusion from the shoot may be a major mechanism involved in that tolerance.     

Responses of Some Local/Exotic Accessions of Lentil (Lens culinaris Medic.) to Salt Stress

Assessment of salt tolerance at all growth stages is crucial to determine the overall tolerance of a crop. Salt tolerance of five tolerantILL 5845, ILL 6451, ILL 6788, ILL 6793 andILL 6796, three moderately tolerant ILL 6431. ILL 6770 andILL 6784, and three sensitiveILL 6210, ILL 6439 andILL 6778 accessions selected at the germination and seedling stages was assessed at the adult stage using sand culture sahnized with 0, 30, or 60 mol m^?3 NaCl. A positive correlation was observed between degrees of salt tolerance at different growth stages in three tolerant accessionsILL 6451, ILL 6788 andILL 6793 which produced significantly higher seed yield than the other accessions. This was also affirmed in three sensitive and two moderately tolerant accessions (ILL 6770 andILL 6784) whose salt sensitivity was conferred consistently at all growth stages. In contrastILL 5845, andILL 6796 which were highly salt tolerant andILL 6431 which was moderately tolerant at the early growth stages had relatively low seed yield, hence showing a negative correlation between tolerances at different growth stages. High yielding accessionsILL 6451, ILL 6788 andILL 6793 in general, accumulated higher Na⁺ and higher or moderate Cl^? in their shoots compared with the other accessions, thus showing a typical halophytic mechanism of salt inclusion. K/Na ratios of all the tolerant, moderately tolerant and sensitive accessions exceptILL 6784 andILL 6778 were less than 1, a suggested minimum level for normal functioning of many metabolic processes in plants. The present study shows that salt tolerance observed previously at the early growth stages is conferred at the adult stage in most of the accessions of lentil examined here; but for others in which no positive correlation was observed between different growth stages suggests that a combination of certain characters can be used as selection criterion for improving salinity tolerance in lentil through exploitation of inter- and intra-cultivar/line variation.     

Differences in Ion Accumulation and Salt Tolerance among Glycine Accessions

Salinity reduces crop yield by limiting water uptake and causing ion‐specific stress. Soybean [Glycine max (L.) Merr.] is sensitive to soil salinity. However, there is variability among soybean genotypes and wild relatives for salt tolerance, suggesting that genetic improvement may be possible. The objective of this study was to identify differences in salt tolerance based on ion accumulation in leaves, stems and roots among accessions of four Glycine species. Four NaCl treatments, 0, 50, 75 and 100 mm , were imposed on G. max, G. soja, G. tomentella and G. argyrea accessions with different levels of salinity tolerance. Tolerant genotypes had less leaf scorch and a greater capacity to prevent Na⁺ and Cl^? transport from soil solution to stems and leaves than sensitive genotypes. Magnitude of leaf injury per unit increase in leaf Na⁺ or Cl^? concentrations was lower in tolerant than in susceptible accessions. Also, plant injury was associated more with Na⁺ rather than with Cl^? concentration in leaves. Salt‐tolerant accessions had greater leaf chlorophyll‐meter readings than sensitive genotypes at all NaCl concentrations. Glycine argyrea and G. tomentella accessions possessed higher salt tolerance than G. soja and G. max genotypes.     

Characterization of alfalfa (Medicago sativa L.) following in vitro selection for salt tolerance

Summary Alfalfa (Medicago sativa L.) is a valuable forage crop which is grown in areas of limited rainfall, high temperature and where the land is often salt affected. Seedlings of the commercial variety CUF 101 and the more salt tolerant breeding line CUF101-1S were used as explant material to produce tissue cultures for an in vitro screen for salt tolerance. Callus cultures were placed on a regeneration medium containing 0–350 mol m^-3 NaCl to establish the highest possible salt concentration that would allow buds to regenerate and survive as plantlets. Buds were regenerated in 250 mol m^-3 NaCl then isolated, grown to maturity and set seed. The response to salt tolerance in the short term was investigated by exposing 14-day-old seedlings to 200 mol m^-3 NaCl. Measurement of growth, survival, proline concentration and the activity of antioxidant enzymes were made after 14 days exposure to NaCl. One somaclone in particular (6R2IV) compared with the parent line showed increased salt tolerance, greater accumulation of proline and a greater increase in the antioxidant enzyme, glutathione reductase. A potentially important gene is pA9 which is known to be responsible for the production of a proline rich cell wall protein. Polymerase Chain Reaction (PCR) amplification of a region of the pA9 gene indicated that it was present in both tolerant and sensitive lines. Southern blotting has shown that the copy number of the pA9 was present as multiple copies in the tolerant clone compared with a single copy in the parents.Abbreviations GR glutathione reductase     

Understanding physiological and morphological traits contributing to drought tolerance in barley

Drought stress is a major limiting factor for crop production in the arid and semi‐arid regions. Here, we screened eighty barley (Hordeum vulgare L.) genotypes collected from different geographical locations contrasting in drought stress tolerance and quantified a range of physiological and agronomical indices in glasshouse trails. The experiment was conducted in large soil tanks subjected to drought treatment of eighty barley genotypes at three‐leaf stage and gradually brought to severe drought by withholding irrigation for 30 days under glasshouse conditions. Also, root length of the same genotypes was measured from stress‐affected plants growing hydroponically. Drought tolerance was scored 30 days after the drought stress commenced based on the degree of the leaf wilting, fresh and dry biomass and relative water content. These characteristics were related to stomatal conductance, stomatal density, residual transpiration and leaf sap Na, K, Cl contents measured in control (irrigated) plants. Responses to drought stress differed significantly among the genotypes. The overall drought tolerance was significantly correlated with relative water content, stomatal conductance and leaf Na⁺ and K⁺ contents. No significant correlations between drought tolerance and root length of 6‐day‐old seedling, stomatal density, residual transpiration and leaf sap Cl^? content were found. Taking together, these results suggest that drought‐tolerant genotypes have lower stomatal conductance, and lower water content, Na⁺, K⁺ and Cl^? contents in their tissue under control conditions than the drought‐sensitive ones. These traits make them more resilient to the forthcoming drought stress.     

Assessment of tolerance to salt stress in Kenyan tomato germplasm

Tomato is an important vegetable crop in Kenya and the development of salt tolerant cultivars would enhance its productivity in the vast marginal areas of the country. This study was aimed at determining the magnitude of genotypic variability for salt tolerance in the Kenyan tomato germplasm. Pot experiments with 22 landraces and 9 market cultivars were laid out as a two and four replicate split-plot design in glasshouse in Experiments 1 and 2, respectively. Salt treatments in Experiment 1 were 0 and 5 g NaCl kg^-1 resulting into 0.5 and 9.1 dS m^-1 of the soil saturation extracts, respectively. In Experiment 2 the treatments were 0, 4, and 8 g NaCl kg^-1 soil corresponding to 0.5, 7.4, and 14.2 dS m^-1, respectively. Data were recorded on agronomic and biochemical parameters. The germplasm showed large variation for salt tolerance. Fruit and seed production at soil salinity of 14.2 dS m^-1 demonstrated that these tomatoes are fairly tolerant of NaCl. Osmotic adjustment was achieved by higher fruit electrical conductivity, brix and total titratable acidity. Low and high contents of K⁺, Ca²⁺ and Mg²⁺ within tomato tissues and soil, respectively, under salt treatment, confirmed competition and antagonism involving Na⁺ and these cations. Low Na⁺ and Cl^- contents in the fruit at 7.4 dS m^-1 revealed their exclusion and ensured production of physiologically normal seeds and nutritionally healthy fruits. Two landraces ‘Chwerotonglo’ and ‘Nyanyandogo’ were identified as salt tolerant. Comparatively, the market cultivars showed superior fruit yields despite their susceptibility to salinity. Accordingly, tolerance of landraces in combination with superior yields of the market cultivars is suitable for tomato improvement for salt tolerance. This revised version was published online in July 2006 with corrections to the Cover Date.     

蛋白激发子Hrip1基因在拟南芥中表达可提高植株的耐盐耐旱能力

Hrip1是从极细链格孢(Alternaria tenuissima)代谢物中分离的一种蛋白激发子。将蛋白激发子基因Hrip1转化到拟南芥,对5个T₁代转基因拟南芥株系进行分子检测, 证明Hrip1基因能够在拟南芥中转录和表达。转基因植株对盐和干旱胁迫的抗性显著增强, 75 mmol L⁻¹ NaCl和50 mmol L⁻¹甘露醇渗透胁迫2 d, 转基因植株种子平均相对发芽率为32.1%和77.9%, 分别比野生型的增加3.72倍和5.61倍; 150 mmol L⁻¹ NaCl和50 mmol L⁻¹甘露醇处理拟南芥幼苗7 d后, 转基因植株平均相对根长为81.79%和93.25%, 分别是野生型的1.53倍和1.34倍。3周龄的转基因植株在250 mmol L⁻¹ NaCl条件下胁迫20 d, 平均存活率为67%, 显著高于野生型(42%)(P<0.05); 干旱胁迫25 d后, 复水5 d转基因植株平均存活率为72%, 而野生型仅为44%。检测结果显示转基因植株叶片的抗氧化酶活性明显高于野生型, 用200 mmol L⁻¹ NaCl和200 mmol L⁻¹甘露醇处理24 h后, POD活性分别比野生型植株提高1.56倍和1.85倍, CAT活性分别比野生型植株提高1.64和1.86倍。说明蛋白激发子Hrip1基因在拟南芥中的表达能够改善和提高植株的耐盐抗旱能力。     

Differential Cl−/Salt Tolerance and NaCl‐Induced Alternations of Tissue and Cellular Ion Fluxes in Glycine max,Glycine soja and their Hybrid Seedlings

The salt‐sensitive Glycine max N23674 cultivar, the salt‐born Glycine soja BB52 population, and their hybrid 4076 strain (F₅) selected for salt tolerance generation by generation were used as the experimental materials in this study. First, the effects of NaCl stress on seed germination, tissue damage, and time‐course ionic absorption and transportation were compared. When qualitatively compared with seed germination appearance in culture dishes, and tissue damages on roots or leaves of seedlings, or quantitatively compared with the relative salt injury rate, the inhibition on N23674 was all the most remarkable. After the exposure of 140 mm NaCl for 1 h, 4 h, 8 h, 12 h, 2 days and 4 days, the content of Cl^? gradually increased in the roots and leaves of seedlings of BB52, 4076 and 23674. Interestingly, the extents of the Cl^? rise in roots of the three experimental soybean materials were BB52 > 4076 > N23674, whereas those in leaves were just on the contrary. Secondly, by using the scanning ion‐selective electrode technique (SIET), fluxes of Na⁺ and Cl^? in roots and protoplasts isolated from roots and leaves were also investigated among the three experimental soybean materials. After 140 mm NaCl stress for 2, 4 and 6 days, and when compared with N23674, slighter net Cl^? influxes were observed in root tissue and protoplasts of roots and leaves of BB52 and 4076 seedlings, especially at the cellular protoplast level. The results indicate that with regard to the ionic effect of NaCl stress, Cl^? was the main determinant salt ion for salt tolerance in G. soja, G. max and their hybrid, and the difference in their Cl^?/salt tolerance is mainly attributed to the capacity of Cl^? restriction to the plant above‐ground parts such as leaves.     

In vitro selection of wheat callus tolerant to high levels of salt and plant regeneration

Summary Embryogenic calli isolated from immature embryos of four wheat cultivars were subjected to three in vitro selection methods for salt tolerance. The effect of NaCl on the selected and unselected cell lines has been investigated. The results indicated that the relative growth rate of callus decreased as the concentration of NaCl increased in both callus lines. The selected callus line gave a higher growth weight in the presence of NaCl in the medium and was highly significant as compared with unselected callus line across medium protocols in all wheat cultivars. The dry weight of both kinds of callus lines of all wheat cultivars increased markedly with increasing NaCl concentration in most cases. The Na⁺ and Cl^- contents of both callus lines were increased with increasing salinity levels while K⁺ content was decreased. The selected callus line of each cultivar at the same salinity level produced significant amounts of Na⁺, K⁺ and Cl^- higher than the unselected callus line in most salinity levels. However, the unselected callus lines of the cultivars Giza-157 and Sakha-90 at the same salinity level produced significant amounts of K⁺ higher than the selected callus line in most salinity levels. The proline content of both kinds of callus lines for all wheat cultivars was increased with increasing salinity level. However, the selected callus line gave a significantly higher proline content than the unselected callus line in all wheat cultivars at the same Salinity level. Results from the in vitro selection for NaCl tolerance showed that the stepwise method of increasing NaCl in the medium was more effective for plant regeneration than other methods.     

The yield stability of CIMMYT'S maize germplasm

Summary Relationships between whole-plant and germination NaCl tolerance and two in vitro measures of NaCl tolerance were evaluated in lucerne (Medicago sativa L.). No significant correlations were observed between relative NaCl tolerance of non-regenerating callus cultures, herbage regrowth, seed or pollen germination, and pollen tube growth. Simulated selection using indirect measures of NaCl tolerance produced small expected gains in relative NaCl tolerance during herbage regrowth and seed germination. These gains were less than 30% of those expected with direct selection for regrowth or germination tolerance. Selection based on the apparent NaCl tolerance of callus tissue or male gamephytes would appear unproductive. Direct selection for NaCl tolerance both at germination and during mature plant regrowth would appear to be necessary to rapidly develop lucerne populations with field-relevant levels of tolerance to NaCl stress.Approved by the Arizona Agric. Expt. Stn. as Journal Series no. 5015.     

Estimation of salt tolerance in Andrographis paniculata accessions using multiple regression model

The complexity and polygenic nature of the salt tolerance trait in plants needs to develop a multiple indicator in the screening process. The mentioned issue led us to carry out an experiment to identify tolerant genotypes through multiple parameters in Andrographis paniculata. For this purpose, the 40-days seedlings were grown in different salinity levels (control, 4, 8, 12 and 16?dS?m^?1) on Hoagland??s medium. The results indicated that salinity had a significant effect on the morphological, physiological and biochemical traits. All measured morphological traits, and chlorophyll, K⁺ and Ca²⁺ content were significantly decreased with increasing salinity levels, while proline and Na⁺ content increased. The present exploration revealed that, salt tolerance index (STI), using the multiple regression model, demonstrated a more stable trend than the single variable assay (total dry weight). Furthermore, STI based on multiple regression analysis gives an accurate definition of salt-tolerant individuals. Under salt stress, tolerant accessions had high STI and produced higher proline, K⁺ and Ca²⁺, and lower Na⁺ content than sensitive accessions. Cluster analysis based on related traits to STI, indicated high similarity in each group. These outcomes can be utilized to evaluate the salt tolerance threshold in the species and may have a great advantage over conventional methods. Probably, our upshots can be applied in the next breeding programs to develop salt-tolerant varieties.     

Maize genotypes with deep root systems tolerate salt stress better than those with shallow root systems during early growth

Maize (Zea mays L.) is susceptible to salinity but shows genotypic variation for salt tolerance. How maize genotypes with contrasting root morphological traits respond to salt stress remains unclear. This study assessed genotypic variation in salinity tolerance of 20 maize genotypes with contrasting root systems exposed to NaCl for 10 days (0, 50 mM or 100 mM NaCl, added in four increments every other day from 14 days after transplanting, DAT) in a semi-hydroponic phenotyping system in a temperature-controlled greenhouse. Considerable variation was observed for each of the 12 measured shoot and root traits among the 20 genotypes under NaCl treatments. Salt stress significantly decreased biomass production by up to 54% in shoots and 37% in roots compared with the non-saline control. The 20 genotypes were classified as salt-tolerant (8 genotypes), moderately tolerant (5) and salt-sensitive (7) genotypes based on the mean shoot dry weight ratio (the ratio of shoot dry weight at 100 mM NaCl and non-saline control) ± one standard error. The more salt-tolerant genotypes (such as Jindan52) had less reductions in growth, and lower shoot Na⁺ contents and higher shoot K⁺/Na⁺ ratios under salt stress. The declared salt tolerance was positively correlated with shoot height, shoot dry weight and primary root depth, and negatively correlated with shoot Na⁺ content at 100 mM NaCl. Primary root depth is critical for identifying salt responsiveness in maize plants and could be suggested as a selection criterion for screening salt tolerance of maize during early growth. The selected salt-tolerant genotypes have potentials for cultivation in saline soils and for developing high-yielding salt-tolerant maize hybrids in future breeding programmes.     

Screening for Drought Tolerance: Evaluation of Seed Germination and Seedling Growth for Drought Resistance in Legume Plants

Experiments were performed to evaluate seed germination and seedling growth in simulated drought as screening techniques for drought tolerance raring. Several laboratory screening tests were evaluated for ability to estimate drought resistance in 18 cultivars of legume plants (field bean, soybean, field pea, lupine). Drought was simulated by a water solution of mannitol of chemical water potential ψ= -0.3 and -0.6 MPa. Both solutions significantly affected seed germination (final germination and promptness index) and seedling growth parameters (seedling height, dry matter of shoot and root as well as leaf injury by drought and high temperature). The tested cultivars could be grouped as drought resistant and drought susceptible plants. Drought tolerance ratings of legume plants in the laboratory tests were, on the whole, consistent with the ratings based on estimation of direct effects of soil drought on seed yield in field experiments. Measurements of electroconductivity of leaf diffusate to evaluate invisible injury caused by drought or high temperature were found to be an adequate criterion for drought tolerance rating. It is concluded that tolerance to drought stress in growing seedlings can be screened for by using mannitol containing nutrient solution. According to the results collected in this research, varieties differences in seed germination, seedling growth and leaf injury affected by drought or heat temperature were evident, however, not all treatments appeared to be equally useful for screening of legume species cultivars.     

Growth Properties and Ion Distribution in Different Tissues of Bread Wheat Genotypes (Triticum aestivum L.) Differing in Salt Tolerance

Four bread wheat genotypes differing in salt tolerance were selected to evaluate ion distribution and growth responses with increasing salinity. Salinity was applied when the leaf 4 was fully expanded. Sodium (Na⁺), potassium (K⁺) concentrations and K⁺/Na⁺ ratio in different tissues including root, leaf‐3 blade, flag leaf sheath and flag leaf blade at three salinity levels (0, 100 and 200 mm NaCl), and also the effects of salinity on growth rate, shoot biomass and grain yield were evaluated. Salt‐tolerant genotypes (Karchia‐65 and Roshan) showed higher growth rate, grain yield and shoot biomass than salt‐sensitive ones (Qods and Shiraz). Growth rate was reduced severely in the first period (1–10 days) after salt commencements. It seems after 20 days, the major effect of salinity on shoot biomass and grain yield was due to the osmotic effect of salt, not due to Na⁺‐specific effects within the plant. Grain yield loss in salt‐tolerant genotypes was due to the decline in grain size, but the grain yield loss in salt‐sensitive ones was due to decline in grain number. Salt‐tolerant genotypes sequestered higher amounts of Na⁺ concentration in root and flag leaf sheath and maintained lower Na⁺ concentration with higher K⁺/Na⁺ ratios in flag leaf blade. This ion partitioning may be contributing to the improved salt tolerance of genotypes.     

Quantitative trait loci controlling rice seed germination under salt stress

Salt tolerance of rice (Oryza sativa L.) at the seed germination stage is one of the major determinants for the stable stand establishment in salinity soil. One population of recombinant inbred lines (RILs, F_2:9), derived from a cross between a japonica rice landrace tolerant to salt stress and a sensitive indica rice variety, was used to determine the germination traits including imbibition rate and germination percentage under control (water) and salt stress (100 mM NaCl) for 10 days at 30 °C. The multiple interval mapping (MIM) were applied to conduct QTL for the traits. The results showed that seed germination was a quantitative trait controlled by several genes, and strongly affected by salt stress. A total of 16 QTLs were detected in this study, and each QTL could explain 4.6–43.7% of the total phenotypic variance. The expression of these QTLs might be developmentally regulated and growth stage-specific. In addition, only one digenic interaction was detected under salt stress, showing small effect on germination percentage with R² 2.7%. Among sixteen QTLs detected in this study, four were major QTLs with R² > 30%, and some novel alleles of salt tolerance genes in rice. The results demonstrated that the japonica rice Jiucaiqing is a good source of gene(s) for salt tolerance and the major or minor QTLs identified could be used to improve the salt tolerance by marker-assisted selection (MAS) in rice.     

An in vitro assay for drought-tolerant coconut germplasm

Summary The feasibility of developing an in vitro technique for screening drought-tolerant coconut germplasm has been investigated. Embryos excised from mature nuts of Sri Lanka-tall coconut were cultured as described previously. Water-stress in the culture system was progressively increased with each passage, by incorporating polyethylene glycol (PEG-6000), mannitol and sodium chloride into the culture medium. PEG and mannitol were observed to be growth inhibitory in action event at low concentrations and these two compounds were abandoned. In NaCl-stressed media, about 21% of randomly selected Sri Lanka-tall embryos died before reaching the 170 mM NaCl. About 78% survived 170 mM NaCl and only 12.6% were able to resist 320 mM NaCl. When zygotic embryos derived from two known drought-susceptible cultivars of coconut, CRIC-65 and Dwarf (from pumila) were tested using the same technique, 29% and 73% of embryos respectively died due to stress damage caused by 170 mM NaCl and none of either cultivar survived a salt concentration above 230 mM.However, embryos originated from two putative drought-tolerant cultivars showed a higher survival rate when subjected to salt stress. At 170 mM NaCl, all the embryos had developed into seedlings. In fact, percent germination of embryos was somewhat higher in 170 mM NaCl than in the control, that was devoid of NaCl. However, percent survivors gradually dropped with increase in salt concentration and about 18% survived the 330 mM NaCl. The technique seems to have great potential in screening drought-tolerant coconut germplasm.     

Effect of Sodium Chloride on Germination and Seedling Characters of Different Types of Rice (Oryza sativa L.)

The rice eultivars grown in the tropies and sub-tropics can be broadly categorized as aromatic small grain, local coarse grain and modern high yielding varieties (HYV). The first two categories are traditional rice, and are generally palatable. The aromatic rice has better market value than HYV rice, yet farmers are unwilling to expand its cultivation because of the low yield potential. One possibility to expand the cultivation of traditional rice is o t find stress tolerant cultivars for growing in marginal land. The salinity tolerance of nine rice cultivars representing three from each type of aromatic small grains, local coarse grains and HYV types, was analysed at germination and early seedling stage. Seeds were placed for germination and the seedlings were allowed to grow for nine days at NaCl concentrations of 0, 50, 100, 150 and 200 mM. NaCl decreased the germination index (GI), speed of germination, seedling height and seedling dry matter weight. Seedling characteristics were decreased more than GI. In general aromatic small grain type showed more salt sensitivity than the other two types. Among the nine cultivars Shakkorkhora (aromatic type) showed the least salt tolerance in relation to germination and seedling characters while the other two cultivars of the same group showed tolerance as high as the tolerant cultivars in other types. Generalization of group salt tolerance of rice, therefore, has little value from the agronomic point of view at least at early growth stage. As the number of cultivars employed in this study was only three from each type it is suggested that more cultivars be considered for the purpose of salt tolerant improvement programme of various types of rice.