Plant Regeneration from Protoplasts of Trifolium repens and Lotus corniculatus

Protoplasts were isolated from leaves of Lotus corniculatus and Trifolium repens and from cotyledons of L. corniculatus. These protoplasts divided and produced colonies. The plating efficiency of protoplasts of both species was improved when agarose was used as a supporting medium. Plants were regenerated more regularly and in larger numbers from colonies of L. carniculatus than T. repens. The use of a culture line of T. repens that had been selected for its response in culture markedly increased the proportion of protoplast-derived cultures which regenerated shoots. One regenerant of T. repens (P6) was analysed for morphological and cytalogical variation. This plant was abnormal and highly aneuploid with a wide range of chromosome numbers.     

Effects of Stocking Rate and Overseeding with Red Clover on Productivity of Native Pasture Continuously Grazed by Yearling Steers

Overseeding with red clover (Trifolium pratense L.) and stocking rate are factors that can affect composition and production of hill land pasture. A grazing experiment utilizing yearling beef steers ( Bos taurus) was conducted using 3, 4, and 5 yearling steers ha⁻¹ (285 kg), on native pasture (predominantly Poa pratensis L.) overseeded with red clover and non overseeded. Paddocks of 1 ha were continuously set stocked from mid May to the end of Sept. Herbage mass, herbage consumed and the percentage of legumes, grasses, dead material, and non-leguminous broadleaf plants were recorded. Animals were weighed at the initiation and end of each grazing season and at 4 week intervals. Overseeding increased legume content 4-fold the seeding year but much of this increase was lost the following year. Herbage mass was greater on overseeded pasture the year following seeding but no effect on animal productivity was found. Stocking rate did not affect percentage legume but the proportions of other broadleaf plants increased at high stocking rates. Average daily gain as well as total gain ha⁻¹ was greatest at 4 steers ha⁻¹.     

Contribution of White Clover Varieties in High-Productivity Systems under Grazing and Cutting

Two medium leaf size varieties of white clover (Trifolium repens L.) were grown in mixture with a range of grass species and varieties in a field experiment conducted over 4 years. The clovers were grown singly or as a blend in swards with a tetraploid perennial ryegrass (Lolium perenne L.), a diploid Italian ryegrass (Lolium multiflorum L.) or tetraploid hybrids between these two species (Lolium x boucheanum Kunth). These grasses were also grown in monoculture. Swards were managed in a regime involving two periods of sheep grazing, two periods of cattle grazing and a silage cut in the same year for 4 years. The objectives of this experiment were 3‐fold: (1) to examine the yield and persistency of white clover in highly productive systems with modern perennial, hybrid and Italian ryegrasses; (2) to compare the performance of white clover varieties grown singly in mixture with grasses with their performance together as a blend, and (3) to examine the persistency of new Italian ryegrass varieties, exemplified by AberComo. The clover content of the sward remained high throughout the experiment, with a mean of 31 % overall. Differences in clover yield between plots were largely attributable to the effects of companion grasses. Total yields were very similar in plots containing different clover varieties and in plots where these varieties had been grown singly or as a blend. Grass yields in mixture were greater than those in monoculture but showed similar relative rankings. The diploid Italian ryegrass variety AberComo showed an unexpectedly high yield in the 4th year of the experiment. The implications of these results for strategies for productive, sustainable agriculture using modern white clover and ryegrass varieties are discussed.     

Ultrastructure of Seed Coat Development in the Natural Tetraploid Trifolium pratense L.

Seed coat development in the natural tetraploid Trifolium pratense L. was studied by electron microscopy. The mature seed coat derived from the outer integument is composed of three layers of cells. The cells of the outer epidermis divide anticlinally and undergo radial elongation to form a macrosclereid layer. The cells are characterized by thin walls, the presence of amyloplasts, and numerous vacuoles which are completely or incompletely filled with tannin. The outer tangential walls are thickened at an early stage. An electron-translucent cap develops in the outer tangential walls of the macrosclereid cells at the globular embryo stage. Osteosclereid cells are highly vacuolate with densely staining cytoplasm. Gradually, extensive intercellular spaces are formed. The parenchyma cells are small and have prominent intercellular air spaces. Maturation eventually leads to the disappearance of cytoplasm in all cells, and the compression of the cells of the parenchyma layer.     

高效表达黑曲霉PhyA基因改善白三叶草对有机态磷的利用

利用子叶下胚轴为外植体，通过农杆菌(Agrobacterium tumefaciens) Ti质粒介导遗传转化途径，建立了高效表达黑曲霉PhyA基因的白三叶草转基因系。PCR和Southern印迹结果表明，PhyA基因已整合到转基因植株的基因组中。Northern印迹结果表明，部分转基因系中的PhyA基因具有高表达水平。此外，PhyA基因表达的植酸酶在Patatin信号肽的引导下具有分泌至细胞间隙和根际的能力。与未转基因对照相比，在以植酸盐为唯一磷素供源的条件下，高表达PhyA的转基因系植株的磷素累积量、鲜重和干重显著增加。证明外源转化黑曲霉PhyA基因能显著增强白三叶草利用有机态磷的能力。     

Symbiotic Nitrogen Fixation of White Clover in a Mixed Sward is not Limited by Height of Repeated Cutting

The aim of this study was to investigate whether symbiotic nitrogen fixation in white clover nodules limits nitrogen supply and hence clover growth by repeated defoliation at two cutting heights. Other possible factors governing symbiotic nitrogen fixation in the field were also elucidated. Using ¹⁵N, a 2-year field experiment including white clover ( Trifolium repens L. cv. Ladino) and perennial ryegrass ( Loliumperenne L. cv. Bastion) in monocultures and in mixtures was conducted in Eschikon, Switzerland. The effect of two cutting heights (4 cm and 10 cm above ground level) on the performance of symbiotic nitrogen fixation of white clover in the different sward-types was investigated. After each harvest, the plots were fertilized with 3 g N m^-2(equivalent to 30 kg N ha^-1 cut^-1 or 210 kg N ha^-1 year^-1). In both years, white clover grown in a mixture with grass received a significantly higher percentage of nitrogen from symbiotic fixation compared with clover grown in monoculture. This phenomenon is attributed to the strong competitiveness of ryegrass in soil nitrogen uptake. Consequently, white clover in the clover-ryegrass mixture was more dependent on symbiotic nitrogen fixation than that grown in monoculture. The cutting height did not preferentially influence symbiotic nitrogen fixation, as opposed to the uptake of mineral nitrogen from the soil. From this finding it is suggested that symbiotic nitrogen fixation did not limit the supply of nitrogen to clover and hence its growth. It is proposed that symbiotic nitrogen fixation in white clover is regulated by the demand for nitrogen rather than by the availability of carbohydrate reserves in the stolons. Symbiotic nitrogen fixation should thus be looked upon as an integrated plant growth factor and not as an isolated phenomenon.     

白三叶草坪春季昆虫群落构成的研究

对白三叶(Trifolum repens.L.)草坪春季昆虫群落系统进行了调查及分析,结果表明：白三叶草坪春季昆虫群落由9目28种组成。其中蚜虫、叶螨是春季昆虫群落的优势种。在白三叶草坪昆虫群落演替中,通过对N, S, T, H四个指数的分析,表明4月份昆虫群落比较旺盛,但5月份昆虫群落结构更稳定协调。这些研究为白三叶草坪害虫综合治理提供依据。     

Variation in Crown and Root Organic Reserves Among Lucerne Genotypes of Different Morphology and Flower Colour

Previous evidence indicates that differences in the concentration of underground organic reserves can drive the survival and growing ability of lucerne under cold and defoliation stresses. In order to provide the selection process with further information on compounds that may influence plant performance under grazing, we assessed variations in cold‐season concentrations of nitrogen and carbon reserves on genotypes that had been identified for morphological features that possibly enhance grazing tolerance. The selected genotypes encompassed distinct morphological patterns (defined as ‘models’) and different taxa within the Medicago sativa complex, as shown by different flower colours. Crown concentrations of reserves were determined on 90 genotypes, whereas root concentrations were measured on a subsample of 15 genotypes. Wide intergenotypic variation was observed for all reserve substances. Comparisons among models and among flower colour classes highlighted the high concentrations of crown carbohydrates and root and crown‐soluble proteins of the model coded as ‘D1’, characterized by prostrate, rhizomatous habit and long dormancy, which largely corresponded to plants with yellow or variegated flowers, typical of ssp. falcata and × varia, respectively. There was a strong ‘flower colour × storage organ’ interaction for sugar concentration, and the results suggested a preferential compartment of sugars in the roots of purple‐flowered genotypes that belonged to the ssp. sativa. A rank correlation analysis indicated a positive relationship between persistence after two years under grazing of half‐sib progenies deriving from 19 genotypes out of the 90 and crown concentrations of carbohydrates of the 19 mother plants.     

Effect of Variety and Seeding Rate on Establishment and Productivity of Alfalfa Sown in Autumn

Five alfalfa varieties (var.) were sown on 26 September, 1983 near Aleppo on clay or heavy clay soils, classified as Vertisols (FAO-system) or Chromoxerertic (Calcic) Rhodoxeralf (USDA-system). Irrigation was applied after planting to ensure uniform germination. Thereafter the study was conducted under supplementary irrigation. The parameters measured to estimate fresh weight (FW) and dry matter (DM) yields; plant height, ground cover and regrowth after cutting, indicated that winter-active var. ( Moapa 69, CUF 101 and Aleppo local ) resulted in better productivity than semi-dormant ( Paravivo ) and dormant ( Lebanon local ) varieties. The 2-years mean average FW yields were 70.2, 68.2, 65.2, 57.1 and 36.9 t/ha, or 16.2, 16.0, 15.5, 13.1 and 8.9 t/ha DM respectively. Forage yields were similar among the 12, 16 and 20 kg/ha seeding rates, indicating little justification for high seeding rates under good establishment conditions, even if a seeding-year yield is desired. In general, seeding rate had also no effect on plant population, which was reduced with time and towards the end of the tested period it became nearly similar and counted 137, 132 and 134 plants/m² according to the seeding rates respectively. Alfalfa yields were positively correlated with plant height, ground cover and regrowth after cutting. The highest yielding combination for FW and DM yields in Moapa 69 with 12 kg/ha seeding rate.     

The Effect of Seeding Rate and Nitrogen Fertilization on Barley Yield and Yield Components in a Cool Maritime Climate

Soil and climatic conditions in Newfoundland are on the margins of agricultural capability, and almost all feed grain is imported. The overall objective of this work was to develop guidelines for the production of barley in Newfoundland, with the goal of establishing modern cropping recommendations. We conducted a 4-year study near St. John's to examine the effect of seeding rate and topdress ammonium nitrate (N) fertilization rate on Chapais six-row barley ( Hordeum vulgare L.) yield components and grain yield. Increasing seeding rate from 200 to 380 seeds m^–2 did not alter grain yield in any year. Increasing topdress fertilization from 0 to 60 kg N ha^–1 increased spike density m^–2 at harvest, resulting in linear increases in grain yield in all years. Highest N rates had greatest lodging in two years. Based on our results, agronomic recommendations for eastern Newfoundland now include barley seeding rates of 250 ± 50 seeds m^–2, with topdress applications up to at least 30 kg N ha^–1.     

Bulked AFLP analysis for the assessment of genetic diversity in white clover (Trifolium repens L.)

The use of bulked leaf samples from individual plants for amplified fragment length polymorphism (AFLP) analysis was evaluated as a tool for assessment of genetic diversity in white clover (Trifolium repens L.). Bulking of leaf samples produced slightly simpler AFLP profiles compared to the combined profiles of individual plants from the same cultivar. Approximately 90% of bands which were present in individual plants were present in bulked samples of the same cultivar. The majority of those absent were rare bands, shared by less than 25% of individual plants. Replicate bulk samples gave almost identical banding patterns, demonstrating the robustness of the bulked AFLP technique. Cluster analysis of AFLP data derived from individual plants resulted in a phenogram similar to that produced from data derived from bulked samples of the same plants. AFLP analysis of bulked samples detected significant amounts of genetic variability among 52 cultivars and accessions with genetic similarity values ranging from 0.42 to 0.92. However, cluster analysis of AFLP data only partially reflected the geographic origin of cultivars and accessions and was not congruent with cluster analysis based on variation for morphophysiological characters. Bulked AFLP analysis provides a powerful tool for rapid assessment of genetic variability in white clover and may also be used for cultivar identification. This revised version was published online in August 2006 with corrections to the Cover Date.     

西藏拉萨市‘白燕2号’与箭筈豌豆不同混播比较研究

为了提高西藏高寒牧区饲草产量,缓解草畜矛盾。在西藏拉萨研究了‘白燕2号’与箭筈豌豆不同混播比例草地,在适宜刈割时期牧草养分比较研究。结果表明,各混播比例间的产草量、粗蛋白、粗脂肪、粗纤维、粗灰分、Ca和P含量差异显著,混播可显著提高产草量和牧草品质;且随着箭筈豌豆比例的增加,粗蛋白含量随之增加,最高为单播箭筈豌豆达到22.58%。各混播比例以H4为佳,鲜草产量达到7.71 kg/m2、粗蛋白含量达到13.66%、粗脂肪含量达到1.99%、粗纤维含量达到35.99%、粗灰分含量达到6.77%、Ca:P为5.36。在西藏气候适宜的地区可将‘白燕2号’与箭筈豌豆按此比例（箭筈豌豆40%+‘白燕2号’60%）混播推广以改善饲草品质。     

毛乌素沙地主要作物糜子生理生态学特性的研究

系统研究了毛乌素沙地主要粮食作物糜子在自然和水分胁迫条件下生理、生态特性的日变化和季节变化特征.结果表明:(1)由于滩地小环境因子的特殊性,使拔节期滩地糜子的光合速率高于盆栽对照.(2)土壤水分胁迫主要在抽穗期至灌浆期造成植物体内较大的水分亏缺,在拔节期亏缺不明显.(3)水分胁迫使糜子各生长季的光合速率下降,其中轻