Genetic variability among elite red clover ( Trifolium pratense L.) parents used in Chile as revealed by RAPD markers

Red clover (Trifolium pratense L.) is one of the main forage species of temperate regions. Cultivars of red clover are heterogeneous which makes their genetic analysis difficult. We applied RAPDs (Random Amplifed Polymorphic DNA) in order to assess the genetic relationship and levels of genetic variability existing among a group of 16 elite red clover parents organised in four subsets of 4 parents each. Out of 55 primers 21 provided reproducible results. A total of 135 reliable and polymorphic RAPD bands were detected which were used to estimate genetic distances among pair-wise combinations of elite parents. Nei and Li's similarity values ranged from 0.60 to 0.77, with a mean of 0.66, which reflects a rather high genetic variability among the genotypes evaluated. Lower levels of genetic variability, as detected by polymorphic loci and mean heterogeneity values, were detected in a subset of parents selected for resistance to the stem nematode. Cluster analyses resolved the different sets of parents in a manner consistent with what is known from their breeding origins. An Analysis of Molecular Variance detected substantial levels of variation within subsets of parents. RAPDs represent a valuable source of genetic information for red clover breeding programmes. This revised version was published online in August 2006 with corrections to the Cover Date.     

Modelling carbon dynamics in mixed grass–red clover swards

Growth and carbon dynamics in mixed grass–red clover leys were simulated using a growth model for pure stands based on radiation use, allocation within plant and loss of biomass. The model and its parameter values were taken from previous applications of the model to pure swards of grass and red clover grown in the same experiment at the same sites and years.     

Effects of inbreeding on nodal root system morphology and architecture of white clover (<Emphasis Type="Italic">Trifolium repens</Emphasis> L.)

Plants of white clover (Trifolium repens L.) cultivar Crau, a self-fertile Crau genotype, and nine generations of inbred progeny were raised in sand culture in a glasshouse experiment. Digital images of the root systems were made and root morphological characteristics were determined on all the plants. Root architectural parameters were measured on the Crau parent and the S₁, S₄, S₆, and S₉ inbred lines. The clover roots became shorter and thicker with inbreeding but the number of root tips per plant was unchanged. Root architecture (branching pattern) was largely unaffected by inbreeding. It is concluded that inbreeding white clover will lead to shorter, thicker roots, and reduced nutrient uptake efficiency compared with the parent clover. The degree to which these deleterious traits are overcome during the development of F₁ hybrids needs to be determined.     

Variation for reproductive and agronomic traits among T. repens × T. nigrescens third generation backcross hybrids in the field

Interspecific hybridisation with Trifolium nigrescens Viv. is a possible strategy to improve the reproductive potential of white clover (Trifolium repens L.). Following the development of a fertile F1 hybrid, three generations of backcrossing have been carried out usingT. repens as the recurrent parent. Vegetative characteristics, stolon growth and seed yield components of the backcross (BC) 2 and 3 generations, as well as the parental species were measured on spaced plants grown in the field. Leaf size and plant spread of the BC2 and BC3 generations were less than T. repens but there was no difference in plant fresh weight. Numbers of inflorescences per plant and florets per inflorescence of the backcrosses were greater than T. repens however this was not reflected indifferences in seed yield per plant asT. repens had more seeds per floret and per plant than the backcrosses. Differences in stolon length, the proportion of flowering nodes and the pattern of axillary bud development were observed between T. repens and the backcrosses. Significant variation among the BC 3 generation for vegetative and reproductive traits was observed. Individual plants among the BC 3 generation were identified that combine high forage yield, substantial inflorescence production and good fertility, and these will form the basis of further selection. This revised version was published online in August 2006 with corrections to the Cover Date.     

Self-compatibility and heterosis in white clover (Trifolium repens L.)

Inbred lines of white clover (Trifolium repens L.) have been produced utilising the rare self-fertility (Sf) allele. Twenty-two lines of four distinct groups have been maintained through five generations of selfing by single seed descent. Fourteen lines were used in crosses to produce F¹s. Both parents and hybrids were analysed for a range of morphological characters. Positive heterosis for dry matter production was observed in half the hybrids. No other trait showed significant heterosis. The degree of heterosis appears to be related to the extent of variation in morphological characters between the parental lines, some combinations of lines yielding heterotic hybrids in all cases, others in none. The majority of the F¹ hybrids are superior in terms of dry matter production to eight control varieties. This revised version was published online in July 2006 with corrections to the Cover Date.     

白三叶基因工程改良研究进展

白三叶（Trifolium repens L.）作为优良牧草和地被植物具有重要的应用价值。但其耐盐碱、干旱能力差等原因致使应用受到广泛限制,转基因技术的快速发展为白三叶种质创新提供了有效技术手段,为开展白三叶分子育种奠定了基础。本文就近30年来有关白三叶组织培养、转化方法、转基因遗传改良方面的研究进展进行了综述,并对其应用进行了展望。     

Genotypic Differences in Root Hair Deformation and Subsequent Nodulation for Red Clover under Different Additions of Starter N Fertilization

Red clover cultivars, including diploid and tetraploid, are commonly used in legume‐based pasture mixtures. However, information on nodulation under different starter N regimens is limited. We hypothesized that there is genetic variability among different red clover cultivars for nodulation. A root hair deformation assay was conducted using three diploid (AC Christie, Tapani and CRS15) and three tetraploid (Tempus, CRS18 and CRS39) red clover cultivars by inoculating them with Rhizobium leguminosarum biovar trifolii. Nodulation and morphological characteristics of two selected red clover cultivars, AC Christie and Tempus, were determined under five starter N concentrations (0, 0.2, 0.4, 0.8 and 1.6 mg per plant). Inoculation with rhizobia increased root hair deformation with significant interaction across cultivars. Nodulation was delayed under high starter N concentrations, and genotypic differences were evident for days‐to‐nodule initiation. There was a positive quadratic response to starter N for AC Christie and a negative quadratic response for Tempus for nodulation. Tempus had more active nodules (92 %) than AC Christie (73 %). The genetic variability of red clover cultivars should be considered in N fixation studies and their response to availability of initial N.     

覆盖与间作对亚热带丘陵区茶园土壤微生物量的影响

在亚热带丘陵区红壤幼龄茶园经过4年稻草覆盖及间作三叶草田间小区试验，对土壤剖面分析结果表明．稻草覆盖及间作三叶草均能明显增加土壤表层有机C、碱解N、有效P．增加土壤微生物量C、N、P。剖面中土壤有机C、微生物量C、全N、碱解N、土壤微生物量N、全P、有效P、微生物量P随深度的增加而递减。稻草覆盖影响到40cm土层左右，阃作白三叶草影响到20cm左右。0～20cm土层微生物量C／有机CT2〉T3〉T1，3个处理微生物量N／全N在1．02～2．74之间，微生物量P和全P比值在2．27～13．1之间。亚热带丘陵区红壤幼龄茶园土壤微生物量碳与土壤有机碳C、碱解N、微生物量N、有效P、微生物量P具有极显著的正相关关系（P〈0．01），与全N、全P呈显著的正相关关系（P〈0．05）。     

Response of organically managed grassland to available phosphorus and potassium in the soil and supplementary fertilization: field trials using grass–clover leys cut for silage

Abstract. Effective use and recycling of manures together with occasional and judicious use of supplementary fertilizing materials forms the basis for management of phosphorus (P) and potassium (K) within organic farming systems. Replicated field trials were established at three sites across the UK to compare the supply of P and K to grass–clover swards cut for silage from a range of fertilizing materials, and to assess the usefulness of routine soil tests for P and K in organic farming systems. None of the fertilizing materials (farmyard manure, rock phosphate, Kali vinasse, volcanic tuff) significantly increased silage yields, nor was P offtake increased. However, farmyard manure and Kali vinasse proved effective sources of K to grass and clover in the short to medium term. Available P (measured as Olsen-P) showed no clear relationship with crop P offtake in these trials. In contrast, available K (measured by ammonium nitrate extraction) proved a useful measurement to predict K availability to crops and support K management decisions.     

同时接种解磷细菌与丛枝菌根真菌对低磷土壤红三叶草养分利用的影响

【目的】研究解磷细菌和丛枝菌根真菌同时接种,对低磷土壤养分利用的影响。【方法】采用盆栽试验,通过测定生长于石灰性低磷土壤上红三叶草地上部的生物量及氮、磷营养吸收和根际酸性磷酸酶活性,研究丛枝菌根真菌、4种解磷细菌(编号分别为B1、B2、B3和B4)单独接种及同时接种对石灰性低磷土壤植物生长及氮、磷养分利用的影响。【结果】在石灰性低磷土壤条件下,4种解磷细菌单独接种对红三叶草植株地上部的生长和总吸磷量均无促进作用;单独接种丛枝菌根菌或不同解磷细菌与丛枝菌根真菌同时接种,均能显著提高红三叶草地上部干质量和总吸氮、磷量;在同时接种处理中,解磷细菌B4与丛枝菌根真菌间的相互作用对红三叶草的生长和氮、磷营养吸收具有明显的协同效应,能显著提高红三叶草地上部干质量、总吸氮和吸磷量及红三叶草根际酸性磷酸酶的活性。【结论】在石灰性低磷土壤中,解磷细菌与丛枝菌根真菌同时接种,对植物的氮、磷养分吸收具有明显的互作效应,但这种互作效应与解磷细菌和丛枝菌根真菌的种类有关,解磷细菌B4与丛枝菌根菌同时接种效果最佳。