Characterization of novel inbred lines of white clover (Trifolium repens L.). I. Dynamics of plant growth and nodule development in flowing solution culture

Growth, dry matter partitioning between shoots and roots, and extent of nodulation were characterised in four novel self-fertile highly inbred lines (referred to as A, B, C and D) of white clover (Trifolium repens L.) thought to differ fundamentally in their nitrogen relations and therefore regarded as candidate material for genetic mapping. Plants were inoculated with a mixture of three strains of Rhizobium and grown in flowing nutrient solutions without N for 18 d. Half the plants were then supplied with 20 μM NO₃ ^- during a 36 d treatment period, the remaining plants acting as ‘controls’ solely dependent upon N₂ fixation for acquisition of N. Total dry matter production and shoot:root ratios were similar in all lines supplied with NO₃ ^- and in control plants of lines B and C. Growth was severely reduced in control plants of line D and to a lesser extent in control line A. These effects were attributed to a failure to develop effective N₂ fixation capacity after apparently normal infection. Mean nodule size, nodule numbers and nodule d.w. per plant were extremely low in line D compared with the other lines, irrespective of whether NO₃ ^- was supplied. Lines A, B and C differed in the severity with which NO₃ ^- decreased mean d.w. per nodule and total nodule d.w. per plant relative to corresponding control plants, with line C being least sensitive. Nitrate also decreased the total number of nodules per plant relative to control plants after day 14 in all lines except C, and most severely in line B. This revised version was published online in August 2006 with corrections to the Cover Date.     

在受控条件下植物促生菌对扁豆的生长，结瘤和养分积累的效应

Application of plant growth-promoting rhizobacteria (PGPR) has been shown to increase legume growth and development under field and controlled environmental conditions. The present study was conducted to isolate plant growth-promoting rhizobacteria (PGPR) from the root nodules of lentil (Lens culinaris Medik.) grown in arid/semi-arid region of Punjab, Pakistan and examined their plant growth-promoting abilities. Five bacterial isolates were isolated, screened in vitro for plant growth-promoting (PGP) characteristics and their effects on the growth of lentil were assessed under in vitro, hydroponic and greenhouse (pot experiment) conditions. All the isolates were Gram negative, rod-shaped and circular in form and exhibited the plant growth-promoting attributes of phosphate solubilization and auxin (indole acetic acid, IAA) production. The IAA production capacity ranged in 0.5-11.0 μg mL-1 and P solubilization ranged in 3-16 mg L-1 . When tested for their effects on plant growth, the isolated strains had a stimulatory effect on growth, nodulation and nitrogen (N) and phosphorus (P) uptake in plants on nutrient-deficient soil. In the greenhouse pot experiment, application of PGPR significantly increased shoot length, fresh weight and dry weight by 65%, 43% and 63% and the increases in root length, fresh weight and dry weight were 74%, 54% and 92%, respectively, as compared with the uninoculated control. The relative increases in growth characteristics under in vitro and hydroponic conditions were even higher. PGPR also increased the number of pods per plant, 1 000-grain weight, dry matter yield and grain yield by 50%, 13%, 28% and 29%, respectively, over the control. The number of nodules and nodule dry mass increased by 170% and 136%, respectively. After inoculation with effective bacterial strains, the shoot, root and seed N and P contents increased, thereby increasing both N and P uptake in plants. The root elongation showed a positive correlation (R2 = 0.67) with the IAA production and seed yield exhibited a positive correlation (R2 = 0.82) with root nodulation. These indicated that the isolated PGPR rhizobial strains can be best utilized as potential agents or biofertilizers for stimulating the growth and nutrient accumulation of lentil.     

Genetic diversity of rhizobia associated with indigenous legumes in different regions of Flanders (Belgium)

We investigated the diversity of rhizobia isolated from different indigenous legumes in Flanders (Belgium). A total of 3810 bacterial strains were analysed originating from 43 plant species. Based on rep-PCR clustering, 16S rRNA gene and recA gene sequence analysis, these isolates belonged to Bradyrhizobium, Ensifer (Sinorhizobium), Mesorhizobium and Rhizobium. Of the genera encountered, Rhizobium was the most abundant (62%) and especially the species Rhizobiumleguminosarum, followed by Ensifer (19%), Bradyrhizobium (14%) and finally Mesorhizobium (5%). For two rep-clusters only low similarity values with other genera were found for both the 16S rRNA and recA genes, suggesting that these may represent a new genus with close relationship to Rhodopseudomonas and Bradyrhizobium. Primers for the symbiotic genes nodC and nifH were optimized and a phylogenetic sequence analysis revealed the presence of different symbiovars including genistearum, glycinearum, loti, meliloti, officinalis, trifolii and viciae. Moreover, three new nodC types were assigned to strains originating from Ononis, Robinia and Wisteria, respectively. Discriminant and MANOVA analysis confirmed the correlation of symbiosis genes with certain bacterial genera and less with the host plant. Multiple symbiovars can be present within the same host plant, suggesting the promiscuity of these plants. Moreover, the ecoregion did not contribute to the separation of the bacterial endosymbionts. Our results reveal a large diversity of rhizobia associated with indigenous legumes in Flanders. Most of the legumes harboured more than one rhizobial endosymbiont in their root nodules indicating the importance of including sufficient isolates per plant in diversity studies.     

Cultivar × rhizobial strain interactions in peas with respect to early symbiosis, nodule initiation and N uptake

Sixteen pea cultivars differing in their phenotypic characteristics were studied in order to characterize the cultivars' variability in symbiotic characters using three Rhizobium leguminosarum biovar viceae strains. The peas did not show any cultivar × strain interactions with the rhizobial strains used with respect to root hair infection frequency or day of nodule initiation. Three cultivars had high root hair infection frequencies, and five had only a few infected root hairs. Four of five leafless/semi-leafless varieties investigated and one cultivar with normal leaves formed nodules quickly, whereas three varieties with normal leaves formed nodules slowly. Ten of the cultivars showed cultivar × strain interactions with respect to N uptake, indicating that the performance of the N2-fixing symbioses depends on the rhizobial partner. Six cultivars showed cultivar × strain interactions with respect to dry matter production and the nodule proportion of the dry matter. Of the cultivars investigated, we conclude that some of the leafless/semi-leafless varieties (‘Capella’, ‘Filby’ and ‘Solara’) are suitable for inclusion in a future breeding programme, since these cultivars combined several important symbiotic characters.     

几种土壤及其铁锰结核中粘粒矿物组合的研究

以我国几种常见土壤及相应土壤铁锰结核为试验材料,应用Ｘ－射线衍射,研究了土壤和铁锰结核中层状硅酸盐和氧化铁的类型组合。结果表明：１）从南到北,从供试红壤到砂姜黑土,其层状硅酸盐矿物组合变化表现为由１：１型高岭为主变为以２：１型水云母为主,１．４ｎｍ矿物中由１．４ｎｍ过渡矿物转变为蛭石;从不含蒙脱石到含有一定量的蒙脱石。供试铁锰结核与相应土壤中的层状硅酸盐矿物组合及含量消长趋势在总体上基本一致。２）     

2，4-D对麦苗的刺激、抑制和致瘤效应的研究

 低浓度2，4-D溶液作用于麦苗的不同部位，产生不同的生理效应。以1.5ppm的2，4-D溶液喷于麦苗茎、叶，对小麦生长有刺激作用，但根部不形成瘤状物；如以同样浓度的2，4-D溶液浇根，麦苗根部形成瘤状物，但麦苗植株生长受到抑制。用抗药性标记的田菁茎瘤菌（Azorhizobium caulinodans）接种，证明在30%左右的麦瘤中有该菌进入，但这种麦瘤测不出固氮酶活性，说明麦瘤中少量茎瘤菌是随机性的被动进入，也没有与小麦植株建立共生关系。     

广西黎塘岩溶区富含铁锰结核土元素迁移特征

[目的]研究广西黎塘岩溶区土壤富含铁锰结核背景下元素含量与迁移特征,为富含铁锰结核土的有效修复提供理论依据.[方法]选择具有代表性的未受农业耕作影响的富含铁锰结核土为试验样地,其成土母岩为碳酸盐岩,以成土母岩为碎屑岩的土壤为对照,分层采集剖面A(0~35 cm)、B层(>35 cm)土壤及对应岩石样品,测定土壤、岩石氧化物及重金属元素含量.[结果]广西黎塘岩溶区土壤主要是Si、A1和Fe的氧化物,三者之和在土壤剖面A、B层的平均含量分别占总量的86.32%和86.30%;广西黎塘岩溶区土壤的SiO2和Fe2O3含量均低于对照,而Al2O3、CaO和MgO含量高于对照.广西黎塘岩溶区土壤Cd、Pb和Zn含量顺序为Zn>Pb>Cd,其中剖面A层Cd和Pb平均含量均超过B层,而Zn平均含量低于B层,剖面A、B层Cd、Pb和Zn平均含量均已超过广西土壤元素背景值及成土母岩为碎屑岩的土壤,未超过土壤环境质量二级标准值.广西黎塘岩溶区土壤以高硅铝系数、低盐基总量淋溶系数为特征,土壤剖面B层风化淋溶强度高于A层,风化淋溶程度整体上高于碎屑岩成土.土壤烧失量(LOI)与SiO2含量、Al2O3含量、硅铝率、盐基总量淋溶系数的相关系数分别为-0.8063、0.7091、-0.8570和-0.2923,土壤剖面A、B层Ca、Mg元素及B层的Cd元素发生了亏损,其他元素均表现为富集或强烈富集.[结论]成土母岩为碳酸盐岩的土壤氧化物、重金属含量、风化淋溶强度、迁移特征等与成土母岩为碎屑岩的土壤具有差异,铁锰结核的存在已造成重金属元素在土壤中的积累并具有潜在污染.     

不同施肥处理对蚕豆根系及根瘤的影响*

 以蚕豆品种89-147为材料，在大田条件下研究了不同施肥处理对蚕豆根系及根瘤的影响。结果表明：单施磷肥和磷钾肥配施在现蕾期和开花期对根系和根瘤生长均有较好的促进作用；单施钾肥在各个时期对根系和根瘤生长的促进作用不大；氮磷钾肥配施对根系生长较好，但在现蕾期和开花期对根瘤生长有抑制作用。从经济产量结果看，氮磷钾肥配施的产量最高，其次为单施磷肥和磷钾肥配施，单施钾肥增产效应不大。     

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为大豆的高产栽培提供参考,进行净作大豆(T1),净作大豆十钼肥拌种(T2,播种大豆前取5 g钼酸铵用温水完全溶解,然后加水至0.5 kg,即为1％钼酸铵溶液,然后拌种),间作大豆(T3),间作大豆十钼肥拌种(T4)栽培试验.结果表明:净间作条件下,钼肥拌种大豆能明显改善地上部的农艺性状,T2处理大豆的叶片叶绿素含量比T1处理增加28.9％、T4处理比T3处理增加15.1％;单株根瘤数T4处理为47.2个/株,比T3处理增加24.5％,且比T2处理增加12.9％;净间作大豆的根系活力分别比相应对照增加55.8％和33.6％,产量分别增加550.25 kg/hm2和340.4 kg/hm2,增产幅度为23.4％和38.03％.钼肥拌种处理能够显著增加净间作大豆株高,促进根瘤数增多、根瘤体积增大、固氮能力提高,进而叶片叶绿素含量增加、光合能力增强,从而提高大豆产量.     

田菁生育期间根瘤菌固氮作用和木质素积累研究

本试验研究了田菁生育期间新老根瘤更替和根瘤菌固氮作用,干物质 C/N 比和木质素累积。试验结果表明:1.田菁生育过程中有旺盛的新老根瘤的更替。主茎一真叶有效根瘤在主根上发生,主根有效根瘤教在盛花期达最大值,结荚期则减少16%,而侧根有效根瘤数则增加40.5%,从盛花期至鼓粒期单株有效根瘤数和衰亡根瘤数均增加。2.从盛花期到鼓粒期单株有效根瘤重量显著增加,虽然单位重量有效根瘤固氮酶活性降低,而单株有效根瘤固氮酶活性提高,增加固氮量。3.田菁鼓粒期较盛花期干物质量大并提高干物质 C/N 比和木质素含量,增加单株木质素积累。