Unconditional and conditional QTL underlying the genetic interrelationships between soybean seed isoflavone,and protein or oil contents

Selection for soybean (Glycine max L. Merr.) rich in isoflavones, protein and oil has been difficult due to negative genetic interrelationships. In this study, genetic interrelationships among seed isoflavones and protein and oil contents were evaluated using both unconditional and conditional QTL mapping. Daidzein (DZ), genistein (GT), glycitein (GC) and total isoflavone (TI) contents were analysed in F_5:6, F_5:7 and F_5:8 recombinant inbred lines (RILs) derived from a cross between ‘Zhongdou 27’(TI 3791 μg/g; protein content 42.84%; oil content 18.73%) and ‘Jiunong 20’ (TI 2061 μg/g; protein content 34.05%; oil content 21.42%). When DZ, GT, GC and TI were analysed for their genetic relationships with protein or oil contents, eight conditional QTL were detected, which included DZ|pro, GC|pro, GT|pro, TI|pro, DZ|oil, GC|oil, GT|oil and TI|oil. Seventeen QTL that had significant genetic associations between seed isoflavone, and seed protein or oil contents were found, including two for DZ conditioned on protein (qDZ|proK‐1, qDZ|proF‐2); one for GC conditioned on protein (qGC|proM‐1); three for GT conditioned on protein (qGT|proM‐1, qGT|proA2‐1, qGT|proL‐1); three for TI conditioned on protein (qTI|proM‐1, qTI|proA2‐1, qTI|proF‐2); one for DZ conditioned on oil (qDZ∣oil K_1); one for GC conditioned on oil (qGC∣oilI_1); four for GT conditioned on oil (qGT∣oil A2_1, qGT∣oil F_1, qGTF_2, qGT∣oilD2_1); three for TI conditioned on oil (qTI∣oilA2‐1, qTI∣oilE‐1, qTI∣oilL‐1). Few epistatic interactions among loci were detected. These loci may be valuable for improving seed isoflavone, protein and oil contents.     

Irrigation Level Affects Isoflavone Concentrations of Early Maturing Soya Bean Cultivars

Field experiments were conducted in 2003/2004 in Québec to determine the effects of irrigation levels (none, low and high) and cultivars (AC Orford, AC Proteina and Golden) on soya bean [Glycine max (L.) Merr.] isoflavone concentrations and yields. Seed yield, yield components, and oil and crude protein (CP) concentrations were concurrently determined. Response to irrigation was greater in 2003, which was substantially warmer and drier than in 2004. In both years, most responses were observed with the lower of the two irrigation levels evaluated, which increased total isoflavones concentration by an average of 45 % compared with a non‐irrigated control. Cultivars, however, responded differently to irrigation. In 2003, response of AC Proteina was greater than that of AC Orford, while Golden did not respond. In 2004, some responses were observed with AC Proteina and Golden but none with AC Orford. Overall, in both years, AC Proteina had the greatest isoflavone concentrations and AC Orford the lowest. Responses of seed yield and yield components depended on the year and were also greater in 2003. Both irrigation treatments generally increased seed yield and yield components compared with a non‐irrigated control; the response was greater with the higher irrigation level. Irrigation had no effect on oil and CP concentrations. Finally, isoflavone yield response to irrigation was again greater in 2003, and depended on the cultivar. Results thus demonstrate that specific soil moisture levels will maximize soya bean isoflavone concentrations, excess irrigation sometimes negating any potential benefits.     

Aerial canopy temperature differences between fast‐ and slow‐wilting soya bean genotypes

Drought stress limits crop growth and yield in soya bean (Glycine max [L.] Merr.), but there are relatively few tools available to assess the ability of different genotypes to tolerate drought. Aerial infrared image analysis was evaluated as a potential tool for identifying drought tolerance in soya bean. Drought effects were evaluated from late vegetative to mid‐reproductive stages of soya bean development in an experiment with ten genotypes including five slow‐ and five fast‐wilting genotypes that were from a population derived from Benning×PI416937. There were two deficit irrigation levels for 2 years and one deficit irrigation level for the third year along with a fully irrigated control level. When the canopy was completely closed, relative canopy temperature was determined using an infrared camera taken from an aerial platform 50–75 m above the experiment. As water availability decreased, the relative canopy temperature generally increased. Moreover, slow‐wilting soya bean genotypes generally had lower canopy temperature compared to fast‐wilting genotypes, and grain yield was generally positively associated with cool canopy temperatures. The results indicate that the determination of canopy temperature is a promising tool for rapid characterization of drought‐related traits in soya bean.     

Dynamic quantitative trait loci underlies isoflavone accumulation in soybean seed

Most of quantitative trait loci (QTL) underlying soybean seed isoflavone contents were derived from the harvest stage of plant development, which uncover the genetic effects that were expressed in earlier seed developmental stages. The aim of this study was to detect conditional QTL associated with isoflavone accumulation during the entire seed development. A total of 112 recombinant inbred lines developed from the cross between ‘Zhongdou 27’ (higher seed isoflavone content) and ‘Jiunong 20’ (lower seed isoflavone content) were used for the conditional QTL analysis of daidzein (DZ), genistein (GT), glycitein (GC) and total isoflavone (TI) accumulations through composite interval mapping with mixed genetic model. The results indicated that the number and type of QTL and their additive effects for individual and total isoflavone accumulations were different among R3 to R8 developmental stages. Three unconditional QTL and six conditional QTL for DZ, four unconditional QTL and five conditional QTL for GT, six unconditional QTL and five conditional QTL for GC, six unconditional QTL and seven conditional QTL for TI were identified at different developmental stages, respectively. Unconditional and conditional QTL that affect individual and total isoflavone accumulations exhibited multiple expression patterns, implying that some QTL are active for long period and others are transient. Two genomic regions, Satt144‐Satt569 in linkage group F (LG F; chromosome 13, chr 13) for DZ, GC, GT and TI accumulations and Satt540‐Sat_240 in LG M (chr 07) for TI and GC accumulations, were found to significantly affect individual and total isoflavone accumulations in multiple developmental stages, suggesting that the accumulation of soybean seed isoflavones is governed by time‐dependent gene expression.     

Deficit Irrigation of Soya Bean [Glycine max (L.) Merr.] in a Sub-humid Climate

An experiment was conducted to investigate the influence of different levels of water deficit on yield and crop water requirement of soya beans in a sub‐humid environment (Southern Marmara region, Bursa, Turkey) in 2005 and 2006. One full‐irrigated treatment (T₁), one non‐irrigated treatment (T₅) and three different deficit irrigation (T₂ = 25 % water deficit, T₃ = 50 % water deficit, T₄ = 75 % water deficit) treatments were applied to ‘Nova’ soya bean planted on a clay soil. Non‐irrigated and all deficit irrigation treatments significantly reduced biomass and seed yield and yield components. The full‐irrigated (T₁) treatment had the highest yield (3760 kg ha^?1), while the non‐irrigated (T₅) treatment had the lowest yield (2069 kg ha^?1), a 45.0 % seed yield reduction. T₂, T₃ and T₄ deficit irrigation treatments produced 11.7–27.4 % less seed yield than the T₁ treatment. Harvest index showed less and irregular variation among irrigation treatments. Both leaf area per plant and leaf area index were significantly reduced at all growth stages as amount of irrigation water was decreased. Evapotranspiration increased with increased amounts of irrigation water supplied. Our results indicate that higher amounts of irrigation resulted in higher seed yield, whereas water use efficiency and irrigation water use efficiency values decreased when irrigation amount increased.     

Uncertainty assessment of soya bean yield gaps using DSSAT‐CSM‐CROPGRO‐Soybean calibrated by cultivar maturity groups

Soya bean yield gap can be caused by different factors resulting in uncertainties when the objective is to use such information for farm decision‐making and reference yield determination. Thus, this study aimed to quantify the soya bean yield gap for four sites, located in Southern and Midwestern Brazil, as well as the uncertainties of that related to cultivars, sowing dates, soil types and reference yields. The crop simulation model DSSAT‐CSM‐CROPGRO‐Soybean was calibrated for cultivars with similar maturity groups, based on the data obtained from the best farmers at the county level. The yield gap by water deficit (YG_WD) was obtained through the difference between potential and attainable yields, and that one caused by sub‐optimum crop management (YG_CM) by subtracting actual yield of each county, obtained from official statistics between 1989/90 and 2014/15 growing seasons, from the estimated attainable yield. The yield was simulated using four sowing dates, three soil types and two soya bean maturity groups by county. The reference yield uncertainty was quantified using yield reference from crop model and regional winners of the soya bean yield context, conducted by CESB (Brazilian Soybean Strategic Committee), for the growing seasons from 2013/14 to 2015/16. The crop model showed a good agreement between measured and simulated crop development and growth using calibration by maturity group, with low root mean square error (347 kg/ha). Southern sites had a mean YG_WD of 1,047 kg/ha, while in the Midwest, it was lower than 100 kg/ha. The YG_CM was 1,067, 528, 984 and 848 kg/ha, respectively, for Castro, PR, Mamborê, PR, Montividiu, GO and Primavera do Leste, MT, representing the opportunity for yield gain when having the best farmers as reference. The maturity groups, sowing dates and soil types showed to be an important source of uncertainty for yield gap determination, being recommended to investigate the farms in detail for an appropriate quantification. The reference yield showed expressive uncertainties, with some farmers presenting conditions to increase their soya bean yields by more than 3,000 kg/ha, when considering as reference the yields obtained by the winners’ farmers. These results show that uncertainties must be reduced when assessing farm yield gaps, in order to ensure that expected rate of soya bean yield growth could be reached by adopting the same technologies from CESB winners and best farmers in the county as a reference.     

Yield–Density Relation of Glyphosate-Resistant Soya beans and their Responses to Light Enrichment in North-eastern USA

Optimum plant population densities are a key means of achieving higher seed yield in soya bean [Glycine max (L.) Merr.]. Limited information is available on yield‐density relation of glyphosate‐resistant soya beans in north‐eastern USA. The objective of this research was to determine the appropriate populations for glyphosate‐resistant soya beans, and if the yield potential of glyphosate‐resistant soya bean produced in light‐enriched conditions was affected by populations. Eight glyphosate‐resistant soya bean cultivars with three populations (300 000, 500 000 and 800 000 plants ha⁻¹) were grown under both ambient and light‐enriched conditions in 2002 and 2003. Yield of all cultivars responded to density linearly. As density increased, grain yield was increased by up to 92 % among cultivars. Light enrichment increased yield for all cultivars across the 2 years, although some cultivars were more sensitive. Harvest index either remained unchanged or declined slightly at higher density in 2002, and there was no difference among treatments in 2003. Both pod number and seed number per plant were significantly decreased with the increase of density across the 2 years, while seeds per pod declined slightly or remained unchanged. Greater seed size was obtained in higher density with varied degree depending on cultivars across the 2 years except for those cultivars with relatively larger seed. The increase in seed size by light enrichment was cultivar and density dependent, and varied between years. 800 000 plants ha⁻¹ could be a suitable practice in producing higher yield in north‐east USA for glyphosate‐resistant soya bean. Maintaining the mass of an individual seed is an important strategy in achieving high yield at high population. Establishing mechanisms responsible for the greatest yields via high population under light‐enriched conditions, may provide insights for management and phenotypic improvement.     

Molecular loci associated with seed isoflavone content may underlie resistance to soybean pod borer (Leguminivora glycinivorella)

Soybean pod borer (SPB) (Leguminivora glycinivorella (Mats.) Obraztsov) causes severe loss of soybean (Glycine max L. Merr.) seed yield and quality in some regions of the world, especially in north‐eastern China, Japan and Russia. Isoflavones in soybean seed play a crucial role in plant resistance to diseases and pests. The aim of this study was to find whether SPB resistance QTL are associated with soybean seed isoflavone content. A cross was made between ‘Zhongdou 27’ (higher isoflavone content) and ‘Jiunong 20’ (lower isoflavone content). One hundred and twelve F_5:10 recombinant inbred lines were derived through single‐seed descent. A plastic‐net cabinet was used to cover the plants in early August, and thirty SPB moths per square metre were put in to infest the soybean green pods. The results indicated that the percentage of seeds damaged by SPB was positively correlated with glycitein content (GC), whereas it was negatively correlated with genistein (GT), daidzein (DZ) and total isoflavone content (TI). Four QTL underlying SPB damage to seeds were identified and the phenotypic variation for SPB resistance explained by the four QTL ranged from 2% to 14% on chromosomes Gm7, 10, 13 and 17. Moreover, eleven QTL underlying isoflavone content were identified, and ten of them were encompassed within the same four marker intervals as the SPB QTL (BARC‐Satt208‐Sat292, Satt144‐Sat074, Satt540‐Sat244 and Satt345‐Satt592). These QTL could be useful in marker‐assisted selection for breeding soybean cultivars with both SPB resistance and high seed isoflavone content.     

Drought Tolerance Screening Under Controlled Conditions Predicts Ranking of Water‐Limited Yield of Field‐Grown Soybean Genotypes

Drought is a major limitation to crop yields worldwide. Screening for soybean yield under water deficit is often a bottleneck in breeding programmes. We assessed the validity of a standardized drought tolerance screening method to predict water‐limited field performance of soybean in NW Argentina. First, to determine the phenological period when yield of glasshouse‐grown plants was more sensitive to water deficit, we applied treatments during 21 days in V₇, R₃ or R₅ stages, being the period from R₅ to R₆ the most critical for yield. Afterwards, two glasshouse experiments were carried out to quantify the tolerance of either eight or four genotypes, respectively, by applying a controlled water deficit of constant intensity during the critical period. Finally, yield data obtained in field trials in Argentina across several locations and seasons classified according to rainfall were analysed. Drought Susceptibility Index was calculated for each experiment and for field data, and rankings of tolerance were similar in all cases. This standardized method, which can be automated for high‐throughput phenotyping, could represent a useful tool in breeding programmes for identifying soybean cultivars with improved performance under drought conditions.     

Molecular mapping of a new gene for resistance to frogeye leaf spot of soya bean in 'Peking'

Amplified fragment length polymorphism (AFLP) and microsatellite (simple sequence repeat, SSR) techniques were used to map the _RGSp_eking gene, which is resistant to most isolates of Cercospora sojina in the soya bean cultivar ‘Peking’. The mapping was conducted using a defined F₂ population derived from the cross of ‘Peking’(resistant) בLee’(susceptible). Of 64 EcoRI and MseI primer combinations, 30 produced polymorphisms between the two parents. The F₂ population, consisting of 116 individuals, was screened with the 30 AFLP primer pairs and three mapped SSR markers to detect markers possibly linked to Rcs_Peking. One AFLP marker amplified by primer pair E‐AAC/M‐CTA and one SSR marker Satt244 were identified to be linked to Res_Peking. The gene was located within a 2.1‐cM interval between markers AACCTA178 and Satt244, 1.1 cM from Satt244 and 1.0 cM from AACCTA178. Since the SSR markers Satt244 and Satt431 have been mapped to molecular linkage group (LG) J of soya bean, the Res_Peking resistance gene was putatively located on the LG J. This will provide soya bean breeders an opportunity to use these markers for marker‐assisted selection for frogeye leaf spot resistance in soya bean.     

Selection of soybean mutant lines with altered seed coat colour and their antioxidant activity

In this study, the flavonoid and isoflavone contents in four checks with seed coat colour altered from yellow to black were determined, and their antioxidant activity was measured. Three anthocyanins (delphinidin‐3‐O‐β‐D‐glucoside, D3G; cyanidin‐3‐O‐β‐D‐glucoside, C3G; and petunidin‐3‐O‐β‐D‐glucoside, Pt3G) were detected in the four checks, while their controls (cvs. ‘Danbaek’ and ‘Daepung’) were not found. Among them, D‐16 derived from cv. ‘Danbaek’ showed the highest anthocyanin contents. The isoflavone contents of all checks showed lower levels compared to their controls. Among six isoflavones, glycitein was only detected in DP‐39. To analyse the radical scavenging activities among the four checks, we conducted DPPH, FRAP and UWLA assays. Significant differences in antioxidant activities were obtainable in the four checks, which contained significant differences in levels of anthocyanins and isoflavones. Based on these results, gamma irradiation may change the isoflavone and anthocyanin contents of soybean. Our four checks selected in this study may be useful for breeding soybean varieties to alter their nutritional values.     

Responses of Soya bean Yield and Yield Component Distribution across the Main Axis under Source–Sink Manipulation

Extensive studies have been conducted regarding the source–sink alterations on soya bean [Glycine max (L.) Merr.] yield, but limited information is available for the seed yield and distribution of yield components across main nodes under whole‐plant light‐enriched conditions. A 2‐year research was conducted at the University of Massachusetts Agronomy Farm under ambient and light‐enriched conditions for two old and two new cultivars planted with a normal density. A randomized block design was used in each year. Light enrichment was initiated at the onset of flowering by installing a 90‐cm tall wire mesh fencing (mesh hole size 4–5 cm) adjacent to the centre row and sloping away at a 45° angle and was left in place for the remainder of the growing season. Five source–sink manipulations were initiated following the establishment of light enrichment. The yield sensitivity of the two old cultivars to the changes in source strength and light‐enriched conditions during reproductive period was much greater than that of the two new cultivars. The increased yield by light enrichment in various manipulations of source–sink treatments was, in part, due to increased branch contribution. Most pods were produced at the nodes in the middle sections of the plants and appeared in higher node position in new cultivars compared with the old cultivars. Seed number per pod and seed size was quite uniform across all node positions. Seed size of both the old and the new cultivars was responsive to changes in the source–sink ratio and changes in the environment during the growth of the soya bean plant. The results suggested that soya bean plants showed several mechanisms to control or realize their excess reproductive potential in a constantly changing environment.     

大豆异黄酮组分HPLC快速分析技术及其在豆腐加工中的应用

大豆异黄酮育种与大豆制品加工研究需要进行大批量样品12种异黄酮组分的快速定量分析。在前人研究基础上利用Agilent 1100高效液相色谱(HPLC)系统,以大豆品种南农95C-13为材料,研究大豆苷元,大豆苷,乙酰基大豆苷,丙二酰基大豆苷,染料木苷元,染料木苷,乙酰基染料木苷,丙二酰基染料木苷,黄豆苷元,黄豆苷,乙酰基黄豆苷,丙二酰基黄豆苷等12种标准品外标法快速定量技术。从样品制备与色谱条件对分析12种异黄酮组分的准确度和分离度入手,确定分析流程,以(科丰1号×南农1138-2)的184个重组自交系(NJRIKY)为材料,研究豆腐加工中总量和各组分的变化特点。(1)样品以80%甲醇水溶液50℃超声1 h提取;色谱条件为,检测波长254 nm, 柱温36℃,流速2.0 mL min^–1, 进样量 10 μL, 流动相0.1%(V/V)乙酸水溶液(A)和100%甲醇(B),0~2 min,27% B (V/V)→2~3 min,27%~38% B→3~10 min, 38% B→10~12 min,38%~39% B→12~14 min, 39% B→14~15 min, 39~27% B梯度洗脱;在15 min内将12个组分良好分离,各组分峰面积与其相应浓度均呈良好线性关系(R²为0.9976~0.9999);加标回收率均大于99%,变异系数低于2%。(2)NJRIKY群体籽粒、豆乳、豆腐异黄酮总量和组分的大量分析验证了HPLC快速技术的效果。籽粒异黄酮总含量(3 695.00 μg g^–1)在豆乳加工中平均85.15%转入豆乳 (3 146.12 μg g^–1),14.85% (548.88 μg g^–1)进入豆渣。传统豆腐加工通过硫酸钙絮凝,只有17.32% (639.89 μg g^–1)转入豆腐,67.83% (2 506.23 μg g^–1)留在黄浆水中。豆乳中12种组分含量比籽粒稍低,均以丙酰基染料木苷含量最高;而豆腐中乙酰基染料木苷和乙酰基黄豆苷缺失,以染料木苷元与大豆苷元含量较高。大豆科丰1号与南农1138-2杂交重组后家系间的异黄酮遗传变异增大,增加了对其遗传改良的潜力。     

Characterization of Drought‐Tolerance Traits in Nodulated Soya Beans: The Importance of Maintaining Photosynthesis and Shoot Biomass Under Drought‐Induced Limitations on Nitrogen Metabolism

Drought is the single most important factor limiting soya bean (Glycine max L. Merr.) yields in the field. The following study was therefore undertaken to identify phenotypic markers for enhanced drought tolerance in nodulated soya beans. Leaf and nodule parameters were compared in three genotypes: Prima 2000, glyphosate‐resistant A5409RG and Jackson, which had similar shoot biomass and photosynthesis rates at the third trifoliate leaf stage under water‐replete conditions. When water was withheld at the third trifoliate leaf stage, photosynthesis, nodule numbers, nodule biomass and symbiotic nitrogen fixation (SNF) were greatly decreased. Significant cultivar–drought interactions were observed with respect to photosynthesis, which also showed a strong positive correlation with nodule SNF, particularly under drought conditions. Prima leaves had high water‐use efficiencies, and they also maintained high photosynthetic electron transport efficiencies under long‐term drought. Moreover, Prima had the highest shoot biomass under both water‐replete and drought conditions. A‐5409RG was the most drought‐sensitive genotype showing early closure of stomata and rapid inhibition of photosynthesis in response to drought. In addition to classifying the genotypes in relation to drought tolerance, the results demonstrate that the ability to sustain shoot biomass under nitrogen limitation is an important parameter, which can be easily applied in germplasm screening for drought tolerance in soya bean.     

Old and New Cultivars of Soya Bean (Glycine max L.) Subjected to Soil Drying Differ in Abscisic Acid Accumulation,Water Relations Characteristics and Yield

Two old (Huangsedadou and Longxixiaohuangpi (LX)) and two new (Jindou 19 (JD) and Zhonghuang 30 (ZH)) soya bean (Glycine max (L.) Merr.) cultivars were used to investigate the influence of soil drying on the abscisic acid (ABA) accumulation in leaves, stomatal conductance (g_s), leaf water relations, osmotic adjustment (OA), leaf desiccation tolerance, yield and yield components. The greater ABA accumulation was induced by soil drying, which also inducing g_s decreased at higher soil water contents (SWC) and leaf relative water content (RWC) significantly decreased at lower SWC in the new soya bean cultivars than in the old soya bean cultivars. The soil water threshold between the value at which stomata began to close and the RWC began to decrease was significantly broader in the new cultivars than in the old cultivars. The new cultivars had significantly higher OA and lower lethal leaf water potential than old cultivars when the soil dried. The old cultivars had greater biomass, but lower grain yield than the new cultivars in well‐watered, moderate stress and severe stress conditions. Thus with soil drying, the new soya bean cultivars demonstrated greater adaptation to drought by inducing greater ABA accumulation, stomatal closure at higher SWC, enhanced OA and better water relations, associated with increased leaf desiccation tolerance, greater water use efficiency and higher yield.     

Soya Bean (Glycine max L. Merr.) Genotype Response to Early-season Flooding: II. Aboveground Growth and Biomass

Soya bean is often grown in regions prone to periodic flooding, thus selecting cultivars that maintain production under waterlogged conditions is desirable. An experiment involving flooded soya beans was planted in southern Florida to examine (1) stem and leaf growth; (2) morphological adaptations; and (3) the relationship between early‐season and late‐season flood tolerance in flooded soya beans. Eleven soya bean genotypes previously defined as tolerant or sensitive to flooding were subjected to three treatments at 21 days after sowing (DAS): (1) no flood, (2) 2‐week flood and (3) 4‐week flood. All plants were harvested 49 DAS. Flooded plants exhibited lower stem dry weights but greater partitioning to the stem. Non‐flood treatments had greater leaf dry weight, leaf area and partitioning to leaves than flooded plants. There were positive correlations of genotype stem dry weight and leaf dry weight to early‐season flood tolerance but stem partitioning was negatively correlated with early‐season flood tolerance. Genotypic rankings of early‐season flood tolerance in this study were not correlated with earlier studies basing flood tolerance on seed yield. Our study highlights the range of soya bean morphological adaptations in response to flood. However, our results indicate that early‐season screening may not be an accurate predictor of soya bean genotypic response to late‐season flood.     

Soya Bean (Glycine max L. Merr.) Genotype Response to Early-season Flooding: I. Root and Nodule Development

Soya bean is often grown in regions subject to periodic flooding, with the rooting zone most affected by flooding due to its proximity to the source of stress. Our objectives were to examine the effects of flooding soya bean on its primary roots, adventitious roots and root nodules, and to determine relationships between root morphological changes and early‐season flood tolerance. The experiment was conducted in Belle Glade, FL with 11 soya bean genotypes subjected to (i) no flood, (ii) 2‐week flood 21–35 days after sowing (DAS) or (iii) 4‐week flood 21–49 DAS. All plants were harvested 49 DAS. Flooding reduced soya bean primary root weight, length and volume across genotypes. Adventitious root length and volume were greater in the 4‐week than the 2‐week flood. Soya bean nodule dry weight was threefold higher in the non‐flooded treatments. Genotypic differences in root development and tolerance to flooding were noted, with early‐season flood tolerance correlated with primary root dry weight, length and surface area, and adventitious root dry weight. However, there was no correlation between this study's early‐season root development and late‐season flood tolerance based on seed yield from previous studies. Our results indicate that full season trials may be necessary to identify flood‐tolerant soya bean germplasm.     

A SNP genetic linkage map based on the ‘Hamilton’ by ‘Spencer’ recombinant inbred line population identified QTL for seed isoflavone contents in soybean

Soybean is one of the most important crops worldwide for its protein and oil as well as the health beneficial phytoestrogens or isoflavone. This study reports a relatively dense single nucleotide polymorphism (SNP)‐based genetic map based on ‘Hamilton’ by ‘Spencer’ recombinant inbred line population and quantitative trait loci (QTL) for seed isoflavone contents. The genetic map is composed of 1502 SNP markers and covers about 1423.72 cM of the soybean genome. Two QTL for seed isoflavone contents have been identified in this population. One major QTL that controlled both daidzein (qDZ1) and total isoflavone contents (qTI1) was found on LG C2 (Chr 6). And a second QTL for glycitein content (qGT1) was identified on the LG G (Chr 18). These two QTL in addition to others identified in soybean could be used in soybean breeding to optimize isoflavone content. This newly assembled soybean linkage map is a useful tool to identify and map QTL for important agronomic traits and enhance the identification of the genes involved in these traits.     

Effect of Deep Placement of N Fertilizers and Different Inoculation Methods of Bradyrhizobia on Growth,N2 Fixation Activity and N Absorption Rate of Field‐grown Soybean Plants

The effects of deep placement (supplied at 20 cm depth from soil surface below plants) of 100 kg N ha^?1 of N fertilizers, urea, coated urea or calcium cyanamide (lime nitrogen) on the growth, nitrogen fixation activity, nitrogen absorption rate and seed yield of soybean (Glycine max L. Merr.) plants were examined by comparing them with control plots without deep placement of N fertilizer in sandy dune field. In addition, three different inoculation methods of bradyrhizobia were used for each N treatment: (1) transplantation of 10‐day‐old seedling in a paper pot with vermiculite inoculated with Bradyrhizobium japonicum USDA110, (2) direct transplantation of inoculated 10‐day‐old seedlings, and (3) transplantation of 10‐day‐old seedlings in a non‐inoculated paper pot. The deep placement of N fertilizers, especially calcium cyanamide and coated urea, markedly increased the growth and total N accumulation in shoot, roots and nodules, which resulted in an increase in seed yield. Daily N₂ fixation activity and N absorption rate were estimated by relative abundance of ureide‐N analysed from the concentration of N constituents (ureide‐N, amide‐N and nitrate‐N) in root bleeding xylem sap and increase in total N accumulation in whole plants at R1, R3, R5 and R7 stages. The total amount of N₂ fixation was about 50 % higher in the plants with calcium cyanamide and coated urea deep placements compared with control plants. Deep placement of slow release fertilizers kept nodule dry weight higher in the maturing stage of seed, possibly through abundant supply of photoassimilate to the nodules by supporting leaf area and activity until late reproductive stages. The results indicate that deep placement of calcium cyanamide or coated urea enhances N₂ fixation activity, which ultimately increases the seed yield. The promotive effect was observed with the seedlings transplanted in paper pot with inoculum of bradyrhizobia within any treatments, although nodulation by indigenous rhizobia was observed in the plants transplanted with non‐inoculated paper pot.     

Quantitative trait loci for leafhopper (Empoasca fabae and Empoasca kraemeri) resistance and seed weight in the common bean

A population of 108 common bean recombinant inbred lines (RILs) (F_5:6‐9), derived from a leafhopper (Empoasca fabae and E. kraemeri)‐susceptible cultivar (‘Berna’) and a leafhopper‐resistant line (EMP 419) was used to identify molecular markers genetically linked to leafhopper resistance and seed weight. Bulked segregant analysis and quantitative trait analysis identified eight markers that were associated with resistance to E. fabae, and four markers that were associated with E. kraemeri resistance. Three markers were associated with resistance to both species. A partial linkage map of the bean genome was constructed. Composite interval mapping identified quantitative trait loci (QTL) for resistance to both leaf hopper species on core‐map linkage groups B1, B3 and B7. QTL for seed weight were found close to the locus controlling testa colour and an α‐phaseolin gene.