Inoculation of fumigated nursery soil increases nodulation and yield of bare-root red alder (Alnus rubra Bong.)

To determine if inoculation increases nodulation and yield of bare-root red alder (Alnus rubra Bong.), fumigated nursery plots were treated with inoculum and ammonium sulfate (28 kg N ha^–1) in a factorial experiment. Inoculum was alder soil with 100 infective units of Frankia g^–1. Seedlings were evaluated for nodulation at age 10 wk and when lifted, at age 9 mo. Inoculation produced earlier and more extensive nodulation and increased seedling root collar diameter, height, and dry weight. Fertilization decreased seedling height, but did not decrease nodulation. No interaction of fertilization with inoculation was found. Inoculated unfertilized plots had the highest yield of packable seedlings (257 m^–2), and uninoculated fertilized seedlings had the lowest yield (126 m^–2).     

大豆GmNRT1.2a和GmNRT1.2b基因的克隆及功能探究

拟南芥中硝酸盐的吸收、转运和分配是通过硝酸盐转运蛋白(nitrate transporter, NRT)实现的。尽管之前的生物信息学分析推测大豆GmNRT1.2s可能参与共生固氮过程,但尚未开展相应的功能研究。本研究通过对其表达模式分析収现,GmNRT1.2a和GmNRT1.2b分别在根和叶中高表达,且受硝酸盐诱导,在接种根瘤菌与结瘤因子(nodfactors,NFs)后表达量明显升高。功能研究结果显示,过表达GmNRT1.2a或GmNRT1.2b后大豆根瘤数目显著增加。本研究为深入探究GmNRT1.2a和GmNRT1.2b调控大豆共生固氮过程的分子机制提供了一定的数据支持。     

Effect of Inoculant Rate on Nodulation and Various Agronomic Traits of Soybean

In a soil lacking indigenous Bradyrhizobium japonicum , soybean ( Glycine max [L.] Merr.) nodulation depends upon the number of rhizobia applied with the inoculum. This field study reports the effect of different rates of applied rhizobia on nodulation, dry matter and nitrogen content in soybean in a Mediterranean soil lacking B. japonicum.
Treatments included six rates of B. japonicum , ranging from 2.5 × 10⁴ to 6.075 × 10⁶ rhizobia cells per seed applied to the seed as peat inoculant at planting, 100 kg N ha⁻¹ and an uninoculated control. The experiment was conducted in an Entisol soil. Regression analysis showed linear relationship between the rate of applied rhizobia and the number of the nodules per plant or the dry weight per nodule. In early stages of development (32 and 68 days after planting) plant dry weight was not affected by inoculation rate. At harvest a rate of 7.5 × 10⁴ rhizobia cells per seed was necessary for maximum total and stover dry weight. A higher rate, 6.75 × 10⁵ rhizobia cells per seed, was required to obtain maximum grain yield, total N content in plant tops and grain N content. Grain percentage N was increased up to 2.025 × 10⁶ rhizobia cells per seed. Nitrogen application increased grain yield, total N content and grain N content at the same level as the lower inoculation rate.     

Cellular Defence Reaction of American Cockroach , Periplaneta americana to Metarhizium anisopliae Isolate CQMa102

Injection of conidia solution of Metarhizium anisopliae isolate CQMa102 into the hemocoel of Periplaneta americana caused significant changes of the total hemocytes of the cockroach. P. americana eliminated large amount of the spores efficiently by phagocytosis and nodulation.The experiment shows that the immune system of the cockroach was hardly injured after injected with high dose spores, and the higher dose of spores was injected,the higher mortality of the insect was. However, low dose injection strengthened the immune ability of the insect in certain degree. The saline slightly induced the immune reaction of the insect.     

Screening techniques and improved biological nitrogen fixation in cool season food legumes

Dinitrogen fixation and legume productivity are greatly influenced through the interactions of legume host, Rhizobium, and the above- and below-ground environment. The benefits of improving legume N₂ fixation include reduced reliance on soil N, leading to more sustainable agricultural systems and reduced requirements for fertilizer N, enhanced residual benefits to subsequent crops, and increased legume crop yields. Most of the gains in N₂ fixation to date have been derived from management of legume cropping systems and through inoculation of legume seed with competitive and symbiotically effective rhizobia. Further gains are possible by developing plant cultivars with tolerance to soil abiotic factors, increased plant yield, and a broader and more effective matching of plant host and rhizobia. Techniques for screening material for superior N₂ fixation and examples of programs to increase fixed N, with attention to the major abiotic stresses, are discussed.     

Mutations affecting nodulation in grain legumes and their potential in sustainable cropping systems

Many spontaneous and a large number of induced mutants that show altered nodulation pattern have been isolated in pea, soybean, common bean, faba bean, chickpea, groundnut and pigeonpea. Available information on nodulation mutants in these crops is summarised. The importance of nodulation mutants in basic studies on plant-microbe symbiotic interactions, nitrogen fixation and breeding of cultivars with higher yield and nitrogen fixation rate are examined. The nodulation mutants, after inoculation with specific bacterial strains or a number of different strains, show either: no nodulation (nod-), few nodules (nod+/-), ineffective nodulation (fix-), hyper nodulation (nod++) or hypernodulation even in the presence of otherwise inhibitory nitrate levels (nts). No spontaneous hypernodulation or nts mutants have been found, all have been induced in independent experiments using different cultivars of pea, soybean and common bean after mutagenising seeds. Most nodulation mutants show monogenic recessive inheritance, though semi-dominant and dominant inheritance is also reported. Nodule number is controlled by a process known as autoregulation; hypernodulating mutants show relaxed autoregulation. By grafting shoots of hypernodulating soybean mutant on normal nodulating soybean, mungbean and hyacinth bean, presence of a common, translocatable signal has been shown. Nodulation mutants have contributed to the understanding of the genetic regulation of host-symbiont interactions, nodule development and N fixation. Initially, the hypernodulating mutants were found to be poor in yield. Using the induced hypernodulating mutant, a new soybean cultivar ‘Nitrobean 60’, has been released in Australia. This cultivar is reported to have given 15% higher yield over cv. ‘Bragg,’ and contributed a higher amount of fixed N to the following cereal crop in rotation. Prospects of using the nodulation mutants in developing grain legume cultivars that combine high yield with high residual N, within the bioenergetic constraints, for developing sustainable cropping systems are examined. This revised version was published online in August 2006 with corrections to the Cover Date.     

Rhizobium specificity of Trifolium ambiguum M. Bieb × T. repens L. hybrid clovers

Growth of full-sib families of an F₁ interspecific hybrid between Trifolium ambiguum M.Bieb and T. repens L, and two generations of backcross hybrids (BC₁F₂ and BC₂F₁) with T. repens as the recurrent parent, were compared to their parental species. Plants were grown in a N-free medium and inoculated with Rhizobium leguminosarum biovar trifolii rhizobia effective on T. ambiguum or T. repens. Hybridisation produced progeny that nodulated with rhizobia from either T. ambiguum or T. repens, but plant growth varied. Mean weights of T. repens and hybrids, particularly F₁ and BC₁F₂, were higher when inoculated with a mixture of strains isolated from field grown T. repens than with the New Zealand inoculant strain for T. repens. When inoculated with the mix of rhizobia from T. repens, mean weights were 242, 189, 132, 125, and 100 mg/plant for T. repens, BC₂F₁, BC₁F₂, F₁ and T. ambiguum, respectively. However, although the mean weight of BC₂F₁ lines was significantly less than T. repens, there was considerable variation in individual full-sib families indicating the potential to select within BC₂F₁ hybrids for high plant growth/symbiotic nitrogen fixation. The weight of T. ambiguumplants inoculated with the New Zealand inoculant strain for hexaploid T. ambiguum was similar to T. repens inoculated with the mix of rhizobia from T. repens (253 and 242 mg/plant, respectively). Mean fresh weights of F₁ hybrid plants were similar when inoculated with rhizobia for T. ambiguum or T. repens (125 and 130 mg/plant, respectively). However, weight of T. repens, BC₁F₂ and BC₂F₁ hybrids inoculated with rhizobia for T. ambiguum were all less than 90 mg/plant. There was a significant relationship between plant fresh weight and ethylene production. The results indicate that measuring weights of inoculated plants growing in N-free media is a rapid initial method of screening a range of plant germplasm for plant growth/symbiotic nitrogen fixation rates. This revised version was published online in August 2006 with corrections to the Cover Date.     

抗药性根瘤菌基因工程菌的构建与应用

用三亲本杂交的方法将外源抗药性质粒导入到高效固氮的根瘤菌 Tal377中,外源质粒在 Tal377中能正常表达,但不影响其原有的固氮结瘤能力。利用此抗药性根瘤菌所携带的抗药性,在接种此根瘤菌的同时结合施加一定浓度的抗菌素,抗药性根瘤菌与出发菌株相比表现出一定程度地提高其结瘤固氮能力和占瘤率。