Regulation of root-to-leaf Na and Cl transport and its association with photosynthetic activity in salt-tolerant soybean genotypes

ABSTRACT

Soil salinity is a major constraint to sustainable crop production. Genetic improvements are needed for growing soybean in salinity-prone environments. Salt-tolerant soybean genotypes alleviate a reduction in photosynthesis and growth under saline conditions; however, the detailed mechanisms involved remain unclear. Here, we aimed to clarify how Na and Cl root-to-leaf transport is quantitatively regulated, and to identify whether photosynthetic tolerance depends on traits associated with either stomata or with mesophyll tissues. Two pairs of pot-grown soybean near-isogenic lines (NILs) consisting of tolerant and susceptible counterparts, derived from a cross between salt-tolerant FT-Abyara and salt-sensitive C01, were subjected to salinity treatment in a rainout greenhouse. Comparison of photosynthetic responses between genotypes indicated that genotypic differences in salinity tolerance depended on the ability for sustained CO₂ assimilation in mesophyll tissues, rather than stomatal conductance. The ratio of photosynthetic rate to intercellular CO₂ concentration (A/Ci) declined exponentially with increasing Na and Cl concentration regardless of genotype, but tolerant genotypes effectively kept both elements at significantly low levels. Under saline conditions, tolerant genotypes reduced Na and Cl content at the two transport pathways: from root to stem, and from stem to leaf, but the reduction of Cl at each pathway was only minor. These results suggest that integrating genetic capacity for Cl transport regulation and osmotic adjustment should be an important target in salinity-tolerance soybean breeding.     

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.     

Phenotypic Analyses of Multi-Environment Data for Two Diverse Tetraploid Potato Collections: Comparing an Academic Panel with an Industrial Panel

Phenotypic analyses of two different association panels of tetraploid potato cultivars are presented. Association panels are sets of variously related genotypes assembled for association analysis purposes. The aims of this research were to inspect, analyse and compare two phenotypic data sets, a first step in association mapping analysis. A first panel of 205 contemporary and historical cultivars, selected to represent the commercial potato germplasm pool, was evaluated in two trials in 2006, one on sandy soil and the other on clay soil, both with two replications. It was called the academic panel. Data for the second panel with 299 genotypes were compiled from contributions from five breeding companies and included 66 locations and 18 years. Each of the participating breeding companies contributed data from their clonal selection programmes for 38 advanced breeding clones and a series of standard cultivars. It was called the industrial panel. Variance components for genotypic main effects and genotype-by-environment interactions were calculated, and estimates for the random genotypic main effects were produced. The genotypic main effects for 19 agro-morphological and quality traits were used to study trait by trait correlations within each panel. In addition, for the genotypes shared by both panels, the correlation of genetic main effects between the panels was investigated. The heritability of all traits was high and no large differences were observed between panels. Coefficients of trait variation were highly correlated (r = 0.9) for both panels and trait by trait correlations in both panels showed highly similar patterns. These results demonstrate that a single-year balanced field trial as well as using breeders’ records yields robust phenotypic information that can be used in a genome-wide association study. Issues related to data management and definition of traits are discussed.     

Identification of quantitative trait loci controlling nodulation and shoot mass in progenies from two Brazilian soybean cultivars

Nitrogen (N) demand of soybean [Glycine max (L.) Merrill] can be supplied via biological nitrogen fixation (BNF), however, higher yielding cultivars increase plant demand for N. Phenotypes differing for traits associated with biological nitrogen fixation result from the expression of the multiple genes of both the host plant and the microsymbiont, but limited studies have been done on the genetics of the soybean BNF. Integrated maps of soybean with simple sequence repeat (SSR) markers [Cregan, P.B., Jarvik, T., Bush, A.L., Shoemaker, R.C., Lark, K.G., Kahler, A.L., Kaya, N., Van Toai, T.T., Lohnes, D.G., Chung, J., Specht, J.E., 1999. An integrated genetic linkage map of the soybean genome. Crop Sci. 39, 1464–1491.] offer an excellent opportunity for the identification of traits related to BNF. This study aimed at the identification of quantitative trait loci (QTLs) controlling BNF and nodulation in an F₂ population of 160 plants derived from an intraspecific cross between two Brazilian cultivars, Embrapa 20 × BRS 133, previously identified as having good potential for mapping of QTLs [Nicolás, M.F., Arias, C.A.A., Hungria, M., 2002. Genetics of nodulation and nitrogen fixation in Brazilian soybean cultivars. Biol. Fertil. Soils 36, 109–117.]. From 252 SSR markers tested in the parental genotypes 45 were polymorphic with high heterozygotes resolution. Mapping was performed with those 45 SSR markers for nodulation [nodule number (NN) and nodule dry weight (NDW)] and plant growth [shoot dry weight (SDW)] phenotypes in F_2:3 lines. A total of 21 SSR loci were mapped with a likehood of odds (LOD) value of 3.0 and a maximum Haldane distance of 50 cM, and were distributed in nine linkage groups with coverage of 251.2 cM. The interval mapping analysis with Mapmaker/QTL revealed two genomic regions associated with NN and NDW, with a contribution of putative QTLs of 7.1 and 10%, respectively. The regression analysis identified 13 significant associations between the marker loci and QTLs due to additive effects, with some of them being significantly associated with more than one phenotypic trait. Effects were observed in all variables studied, ranging from 2 to 9%. A one-way analysis of variance (ANOVA) also detected 13 significant associations, related to dominance effects. A two-way-ANOVA showed six epistatic interactions among non-linked QTLs for SDW, NN and NDW, explaining up to 15% of the trait variation and increasing the phenotypic expression from 8 to 28%. The data obtained in this work establish the initial stage for additional studies of the QTLs controlling BNF and indicate that effective marker-assisted selection using SSR markers may be feasible for enhancing BFN traits in soybean breeding programs.     

京411及其衍生系苗期氮和磷利用效率相关性状的遗传分析

为了研究小麦苗期氮、磷吸收及利用效率的遗传差异,以骨干亲本京411及其14份衍生后代为材料,在3个氮处理(Ca(NO3)2含量分别为0、0.05和2.0mmol·L-1)和3个磷处理(KH2PO4含量分别为0、0.005和0.25mmol·L-1)条件下分析不同基因型苗期营养利用效率及相关性状,并结合90kSNP芯片分析氮、磷吸收及利用效率相关遗传区段,以及京411携带的重要区段的传递和分布。结果表明,供试品种(系)的氮、磷吸收及利用效率存在较大遗传变异,京411和CA0958的氮吸收量和农学效率较高,北京0045、中麦175和CA0816R的氮利用效率较高,09抗1027、CA9722、中麦415和CA1133具有较强的耐低氮能力;09抗1027、北京0045和CA1133的磷吸收量较高,中麦175和CA9722的磷利用效率较高,CA0958和北京0045具有较高的磷农学效率,中麦175和CA1055具有较强的耐低磷能力。A和B染色体组在小麦苗期氮和磷吸收及利用中的作用可能大于D染色体组。3B和4B染色体上各存在一个在低磷和高磷条件下对苗期磷利用效率均有影响的位点,1B和2A染色体上各存在一个在不施磷和低磷条件下均表现较强耐低磷能力的位点。氮、磷吸收及利用效率可能具有相同或相似的遗传背景。中麦175与骨干亲本的氮、磷吸收及利用效率相同位点较多,且含有较多的正向效应位点,同时在苗期表现出了较强的氮、磷吸收及利用效率,其在实际生产中表现为高产且水肥利用效率高,是京411的优良衍生后代。     

Yield,protein, and oil quality of soybean genotypes selected for tofu production

The soyfood industry prefers some soybean [( Glycine max L. (Merr.)] cultivars over others based on chemical constituents, physical traits, and processing quality of the seed. However, soybean cultivars possessing the combination of desirable agronomic traits and biochemical characteristics that enhance the quality of soyfoods have not been identified in the U.S. Thus, this research was conducted with the objective of determining yield, seed protein, and fatty acid composition of soybean genotypes selected for tofu production. Twelve soybean genotypes were planted in plots arranged in a randomized complete block design with four replications at the Agricultural Research Station, Fort Valley State University, Georgia during 1994 and 1995. Seed yield ranged from 1.6 to 3.0 metric tons/ha. The protein content varied between 314.2 and 480.7 g/kg seed. Both BARC-8 and BARC-9 had significantly higher protein content than other genotypes. These two genotypes also showed significant year by genotype interactions for some fatty acids. V71-370 had the highest oleic acid concentration and a high ratio (0.92) of monounsaturated to polyunsaturated fatty acids. The concentration of linoleic and linolenic acids ranged from 406.5 to 531.0 and 37.1 to 63.0 g/kg oil, respectively. Seed yield was correlated with biomass, harvest index, and filled pods per m2. In this study, V71-370 was found to be relatively superior in oil quality with fatty acid composition desirable for human consumption. The significant variation for seed yield and biochemical characteristics observed among the few genotypes examined in this study indicates the potential for breeding high yielding soybean cultivars suitable for soyfoods. Therefore, there is a need for evaluation of soybean germplasm for agronomic traits that contribute to seed yield and biochemical characteristics including fatty acid profiles that enhance soyfood quality before initiating development of suitable cultivars for tofu.     

云南间作大豆耐荫性综合评价及鉴定指标筛选

      本文旨在探讨不同基因型大豆品种的耐荫特性，筛选出耐荫性鉴定指标，建立可用于耐荫性评价的数学模型。以44个大豆品种（系）为试验材料，在玉米-大豆间作下创设的自然荫蔽条件开展耐荫性鉴定，净种大豆作为对照。在各参试材料植株成熟期调查10个主要形态性状和产量性状，以各指标的耐荫系数为基础，采用多元统计方法对大豆的耐荫性进行综合评价。结果表明：与对照相比，受荫蔽胁迫后，参试材料的各性状变化趋势及幅度不同，各指标间都有不同程度的相关性，部分性状间相关性达到显著或极显著水平。通过主成分分析，将10个单项指标转换为4个相互独立的综合指标，代表了全部数据79.77%信息量。利用隶属函数法计算综合耐荫评价值（D），并对其进行系统聚类，将44个大豆品种（系）按照耐荫性强弱分为了强耐荫、中等耐荫和弱耐荫3大类。通过逐步回归建立了大豆耐荫性评价数学模型，并筛选出株高、主茎节数、有效分枝数、单株荚数、单株粒数、单株产量、每荚粒数和倒伏8个性状可作为云南省间作大豆耐荫性鉴定指标     

大豆适应低磷胁迫的机理初探

通过营养液栽培试验研究大豆适应低磷胁迫的机理，试图找出供试大豆在水培条件下对低磷胁迫下的适应性与田间表现的关系，为快速选育磷高效品种提供具有参考价值的实验数据。结果表明：在水培条件下，大豆在磷效率方面存在着显著的基因型差异。在总体磷效率(以生物量为标准)方面和磷吸收效率(整株含磷量)方面，结果与田间试验表现基本一致。BX10和GD1属于磷高效对磷不敏感基因型，BD2属于磷低效对磷不敏感基因型，BX11和GD2属于磷低效对磷敏感基因型，BD1属于磷高效对磷敏感基因型，GD3和GD4表现不稳定。从磷的利用效率(单位磷所产生的生物量)来看，基因型间没有显著差异。说明即使在水培条件下，磷利用效率对大豆总体磷效率贡献也不大，大豆总体磷效率主要是由吸收效率决定的。与田间反应不同的是，水培条件下磷吸收效率高的基因型，具有较长的根长与较大的根表面积。说明在介质有效磷分布均匀的条件下，根形态性状对磷吸收效率起一定的作用。     

大豆种质资源共生固氮特性评价及遗传初步研究

以我国２２个省５９０份主要栽培大豆品种为材料,评价春、夏、秋大豆遗传资源结瘤固氮性状,并配制杂交组合进行初步遗传分析,结果显示,１）春夏秋大豆类型间、品种间结瘤固氮性状差异极显著。同类型不同产区的大豆品种共生固氮性状差异显著,以长江流域及其以南产区,尤以湖北、江苏省品种最佳。２）与共生固氮性状密切相关的１０项参数变异范围以夏大豆最大,并鉴定出单株结瘤数达２３８．８个,根瘤重达０．５９ｇ、固氮量达１     

Evaluation of physiological traits as indirect selection criteria for drought tolerance in sugar beet

Drought is the most important limitation to sugar beet (Beta vulgaris L.) production in the UK and other areas dependent on usually insufficient summer rainfall. As increased irrigation is not a viable answer to the problem, an economically and environmentally desirable solution is new varieties with decreased sensitivity to water deficits. However, there is little genotypic information on drought tolerance in sugar beet, and breeders are not equipped to make these selections. The objectives of this study were to assess the degree of genotypic diversity for drought-related morpho-physiological traits and to measure the strength of association between these traits and indicators of crop performance. 46 sugar beet genotypes with diverse genetic backgrounds were tested in three field experiments from 1999 to 2001. Drought was imposed by covering plots with large polythene tunnels, allowing the crop to grow solely on stored soil moisture. Agronomic characters and drought tolerance indices are described in a companion paper [Ober et al., Assessing the genetic resources to improve drought tolerance in sugar beet. Agronomic traits of diverse genotypes under droughted and irrigated conditions. Field Crops Res., in press]. In this report, we show that there were significant genotypic differences for stomatal conductance, succulence index, specific leaf weight, and osmotic adjustment, but not for photosynthetic rate, relative water content or total water use. Patterns of water use within the soil profile differed between genotypes; some extracted more water from deep soil layers. The maintenance of green foliage cover during drought was positively correlated with drought tolerance index, which was negatively correlated with succulence index and scores for wilting and leaf senescence. Droughted sugar yield was positively correlated with soil water extraction and negatively correlated with relative leaf expansion rate measured in late summer. Under irrigated conditions, there was high positive correlation between transpiration rate and sugar yield. Genotype × trait biplots showed superior genotypes with relatively greater expression of combinations of favourable traits. The results suggest that succulence index and wilting score could be used to cull inferior plants in early stages of breeding programs, and green foliage cover and patterns of water use could help identify superior genotypes in elite germplasm. These data should enable tools to be developed for indirect selection of genotypes suited to drought-prone environments.     

不同大豆品种田间结瘤固氮有效性的评价

利用相关和通径分析对田间种植的４０份大豆品种（系）的结瘤固氮性状（结瘤分级，有效瘤数，有效瘤干重，有效结瘤指数，植株干重和植株全氮含量）的研究表明：有效瘤数，有效瘤重和有效结瘤指数可以有效地作为对大豆固氮种质的评价指标，其相对重要性为有效瘤重＞有效瘤数＞有效结瘤指数。在此基础上并结合籽粒产量因子筛选出２份结瘤固氮及产量较高的种质。研究同时也获得了七份在有效瘤重与有效瘤数或有效瘤重与效结瘤指数上表现     

Yield Potential and Waterlogging Tolerance of Selected Near-Isogenic Lines and Recombinant Inbred Lines from Two Southern Soybean Populations

Abstract

A quantitative trait locus (QTL) for waterlogging tolerance has been identified in a northern cultivar Archer. In the current study, Archer was crossed with two southern elite soybean cultivars A5403 and P9641 to investigate the efficiency of marker-assisted selection and phenotypic selection for waterlogging tolerance and to assess the value of waterlogging tolerance for soybean yield improvement. Near-isogenic lines (NILs) were created using the linked simple sequence repeat (SSR) marker Sat_064 for the waterlogging tolerance QTL from each of the F6-derived populations. Concurrently, 103 and 67 recombinant inbred lines (RILs) were also generated from Archer × A5403 and Archer × P9641, respectively. Significant variations in seed yield or plant injury were observed among the NILs and RILs under waterlogging stress. The 29 most tolerant and 29 most sensitive NILs and RILs were selected on the basis of waterlogging injury ratings and evaluated under irrigated and waterlogged conditions in Arkansas and Missouri in 2002 and 2003. The most tolerant lines produced an average of 60.9% of their irrigated yield, as compared with only 32.6% and 53.9% by the most sensitive lines and the commercial checks, respectively. Waterlogging injury scores for the tolerant lines, checks, and sensitive lines were 3.6,4.3, and 6.6, respectively, following the same trend as their yield reductions. A genotype-by-environment interaction (G × E) analysis showed that some of the selected lines were highly stable in response to waterlogging stress across environments. Breeding selection for the waterlogging tolerance can be performed in the field based on seed yield and plant injury scores.     

Genotypic Variation in Biomass Production at the Early Vegetative Stage among Rice Cultivars Subjected to Deficient Soil Moisture Regimes and Its Association with Water Uptake Capacity

References

Genetic improvement in water uptake ability and/or water use efficiency (WUE) of rice cultivars is one option to enhance productivity under water-limited conditions. We examined the genotypic variation in biomass production among 70 rice cultivars (69 cultivars of NIAS global rice core collection and Azucena) under different soil moisture conditions, and to identify whether water uptake ability or WUE is responsible for the variation, if any. Two-week-old seedlings were transplanted into pots and grown for three weeks in an environmentally-regulated growth chamber under three soil moisture regimes: flooded (?0.02 MPa soil water potential) and two unflooded (?0.10 and ?0.52 MPa) conditions. Substantial genotypic variations in total dry weight (TDW) were observed under all three regimes. Among all the cultivars tested, TDW was significantly correlated with water uptake ability, but not with WUE. However, several cultivars exhibited comparably higher WUE while showing superior biomass production under the ?0.52 MPa regime. The amount of water uptake was significantly correlated with root dry weight among cultivars regardless of moisture regimes, while substantial genotypic difference in the amount of water uptake per unit root dry weight was observed. These results indicate that a marked genotypic difference exists in biomass production at the early vegetative growth under water-deficient conditions, and that this difference appears to be ascribed primarily to greater water uptake capacity, and additionally to higher WUE in drought-tolerant cultivars.     

In winter wheat (Triticum aestivum L.), post-anthesis nitrogen uptake and remobilisation to the grain correlates with agronomic traits and nitrogen physiological markers

In wheat, nitrogen (N) uptake and remobilisation after flowering contributes largely, in Northern countries, to grain yield and grain protein content. The aim of our study was first to estimate the proportion of N taken up and remobilised to the grain as well as their relative efficiency using ¹⁵NO₃⁻-labelling at flowering. The validity of the technique was assessed in comparison to the N budget calculation method on five winter wheat cultivars grown for 2 years at low and high fertilization input. We estimated that on average 71.2% of grain N originates from remobilisation with significant genotypic differences. Among the five genotypes, significant differences were also found for both N remobilisation efficiency (from 69.8 to 88.8%) and N translocation efficiency (from 89.7 to 93.4%). In parallel, during 1 year, we monitored physiological markers representative of N assimilation and recycling at two sampling dates during the grain filling period. We then examined if there was any relationship between these physiological markers, N absorption and remobilisation estimates and agronomic traits related to yield and grain N content. Nitrate reductase (NR) activity was highly correlated to N absorbed post-flowering and to grain protein content. Glutamine synthetase (GS) activity was even more highly correlated than NR activity to the amount of N remobilised and grain yield. The use of physiological traits such as NR and GS activities as markers of the wheat N status is discussed.     

耐酸铝根瘤菌的筛选及其对大豆-根瘤菌共生体系的影响

为解决华南大豆种植所面临的土壤酸化问题,筛选出耐酸铝高效根瘤菌,通过回接试验找出适合华南酸性土壤环境的根瘤菌及其共生固氮体系。利用菌株活化培养法分离来自广东增城和惠州地区的20个栽培大豆上的根瘤菌,通过分光光度计检测在酸铝条件下的培养的菌株,筛选出耐性菌株YX30号,并对其生长特性以及接种后对大豆生长的影响。结果表明:在p H4.5及p H6.0条件下含一定浓度铝的营养液中,接种YX30号根瘤菌后,铝浓度为200μmol·L~(-1)时耐酸铝品种华夏1号、PI416937仍能结瘤,桂夏1号和Young不能结瘤。在p H4.5和p H6.0条件下,营养液铝浓度达到100μmol·L~(-1)时,大豆地上部干重均为负增长,铝明显的抑制了大豆的生长;低铝浓度(25和50μmol·L~(-1))条件下,结瘤数均、固氮酶活性、地上部干重及氮含量均高于对照,酸性环境中低浓度的铝能促进结瘤,提高地上部干重和含氮量。     

Morphological and Molecular Characterization of Novel Salt-Tolerant Rice Germplasms from the Philippines and Bangladesh

To screen for new sources of salinity tolerance, 688 traditional rice varieties from the Philippines and Bangladesh were obtained, and their tolerance to hypersaline conditions at the seedling stage was examined. A total of 29 Philippine lines and 15 Bangladeshi lines were scored as salt-tolerant.Morphological assessment(plant height, biomass and Na-K ratio) revealed that among the 44 salt-tolerant accessions, Casibon, Kalagnon and Ikogan had significantly higher relative shoot length difference, relative shoot growth reduction and shoot Na-K ratio than the tolerant check FL478.Additionally, AC and Akundo exhibited significantly higher Na-K ratios than the other genotypes. The genetic diversity of the 44 genotypes was assessed using 34 simple sequence repeat markers. A total of 133 alleles were detected across all loci. Cluster analysis showed that AC, Akundo and Kuplod were clustered along with FL478, indicating a strong genetic relatedness between these genotypes. IR29(susceptible check) was singly separated. The haplotype analysis revealed that none of the 44 genotypes had a similar allele combination as FL478. These accessions are of interest since each genotype might be different from the classical salinity-tolerant Pokkali.     

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.     

Mapping QTLs using a novel source of salinity tolerance from Hasawi and their interaction with environments in rice

Background

Salinity is one of the most severe and widespread abiotic stresses that affect rice production. The identification of major-effect quantitative trait loci (QTLs) for traits related to salinity tolerance and understanding of QTL × environment interactions (QEIs) can help in more precise and faster development of salinity-tolerant rice varieties through marker-assisted breeding. Recombinant inbred lines (RILs) derived from IR29/Hasawi (a novel source of salinity) were screened for salinity tolerance in the IRRI phytotron in the Philippines (E1) and in two other diverse environments in Senegal (E2) and Tanzania (E3). QTLs were mapped for traits related to salinity tolerance at the seedling stage.

Results

The RILs were genotyped using 194 polymorphic SNPs (single nucleotide polymorphisms). After removing segregation distortion markers (SDM), a total of 145 and 135 SNPs were used to construct a genetic linkage map with a length of 1655 and 1662 cM, with an average marker density of 11.4 cM in E1 and 12.3 cM in E2 and E3, respectively. A total of 34 QTLs were identified on 10 chromosomes for five traits using ICIM-ADD and segregation distortion locus (SDL) mapping (IM-ADD) under salinity stress across environments. Eight major genomic regions on chromosome 1 between 170 and 175 cM (qSES1.3, qSES1.4, qSL1.2, qSL1.3, qRL1.1, qRL1.2, qFWsht1.2, qDWsht1.2), chromosome 4 at 32 cM (qSES4.1, qFWsht4.2, qDWsht4.2), chromosome 6 at 115 cM (qFWsht6.1, qDWsht6.1), chromosome 8 at 105 cM (qFWsht8.1, qDWsht8.1), and chromosome 12 at 78 cM (qFWsht12.1, qDWsht12.1) have co-localized QTLs for the multiple traits that might be governing seedling stage salinity tolerance through multiple traits in different phenotyping environments, thus suggesting these as hot spots for tolerance of salinity. Forty-nine and 30 significant pair-wise epistatic interactions were detected between QTL-linked and QTL-unlinked regions using single-environment and multi-environment analyses.

Conclusions

The identification of genomic regions for salinity tolerance in the RILs showed that Hasawi possesses alleles that are novel for salinity tolerance. The common regions for the multiple QTLs across environments as co-localized regions on chromosomes 1, 4, 6, 8, and 12 could be due to linkage or pleiotropic effect, which might be helpful for multiple QTL introgression for marker-assisted breeding programs to improve the salinity tolerance of adaptive and popular but otherwise salinity-sensitive rice varieties.

     

Rhizobial Inoculants for Legume Crops

Summary

Legumes are an important source of protein for humans and livestock. Legumes have also been used for soil improvement for centuries because of their N and non-N rotational benefits to non-legume crops. The N benefits include N₂ fixation and mineralization, sparing of soil inorganic N, and reduced immobilization of soil inorganic N. The non-N benefits include breaking pest cycles, improvement of soil structure, and the nutritional and disease-control effects of endophytic rhizobia. Therefore, optimizing the legume-Rhizobium symbiosis is important, and it can be done by selecting or modifying either (or both) symbiotic partner(s) for desirable traits related to N₂ fixation. Rhizobium strains can be selected or genetically modified for traits like N₂ fixation potential, nodulation competitiveness, persistence in soil, compatibility with inoculant carriers, and tolerance to environmental stress factors. Legume genotypes can also be selected, bred or genetically modified for N₂ fixation potential, restricted or preferential nodulation, and tolerance to nitrate and environmental stress factors. When choosing prospective strains or legume genotypes for a particular environment, time and resources can be saved by realizing that the most adaptable rhizobia or legume genotypes are usually those isolated from similar environments. Inoculant delivery methods also affect N₂ fixation. Soil inoculation, particularly with granular inoculants, seems to be often better and never worse than seed inoculation for initiating nodulation and N₂ fixation. Use of pre-inoculated seeds eliminates the seed inoculation operation, but Rhizobium numbers in pre-inoculated seeds tend to be lower than those in traditional inoculant products. Therefore, the time saved by using pre-inoculated seeds should be weighed against the possibility that crop yields may be lower if insufficient Rhizobium numbers are delivered. Until tools for genetic modification of rhizobia or legumes to suit specific requirements are commonly used, N₂ fixation can be enhanced by adopting practices like choosing the best combinations of Rhizobium strains and legume genotypes, the best inoculant formulation and delivery methods, optimum inoculation rates, and providing favourable growing conditions for the crop.     

Effects of Waterlogging on Nitrogen Fixation and Photosynthesis in Supernodulating Soybean Cultivar Kanto 100

Abstract

The supernodulating soybean (Glycine max (L.) Merr.) cultivar Kanto 100 was previously characterized by superior nitrogen (N) fixation and photosynthesis, and resulting in high yields. However, this cultivar seems to be susceptible to waterlogging during the vegetative growth stage, which frequently occurs in major soybean producing areas in East Asia. The objective of this study was to compare the effects of waterlogging on nodulation, N fixation and photosynthesis in Kanto 100 with those in its normally-nodulating ancestral cultivar Enrei. Kanto 100 and Enrei were grown in pots, and subjected to waterlogging for 10 days at three vegetative growth stages in 2003 and 2004. Waterlogging significantly reduced the number of nodules of both cultivars, but the magnitude of the reduction was more pronounced in Kanto 100. The acetylene reduction activity (ARA) of nodules and apparent photosynthetic rate (AP) of leaves were generally depressed immediately after the start of waterlogging, but both functions recovered substantially at the pod-filling stage in both cultivars. No marked cultivar difference was found in the magnitude of the reduction of ARA per plant and AP measured immediately after waterlogging and at the pod-filling stage in both years, but growth impairment was more pronounced in Kanto 100 in 2003. These results suggest that the supernodulating cultivar Kanto 100 is more susceptible to waterlogging than its normally-nodulating ancestral cultivar.