苜蓿花叶病毒粒子的统计学特征和分组

以一株来自于白车根草（Trifolium repens L.）上的苜蓿花叶病毒分离物AMV-SY为材料,在电镜下观察测量经醋酸铀负染的196个提纯病毒粒子,按其长度分成等距离的5个组,用统计分析方法确定组间的差异。所得各组粒子的平均大小依次是组Ⅰ：(20.4 ±2.5) nm×(18.7±2.3) nm,组Ⅱ：(28.0 ±2.4) nm×(18.1±2.1) nm,组Ⅲ：(36.0 ±2.4) nm×(17.2±2.0) nm,组Ⅳ：(44.8 ±2.7) nm×(16.9±2.0) nm,组Ⅴ：(52.0 ±3.0) nm×(17.4±1.0) nm。它们分别相当于前人根据X-射线衍射或核磁共振所测定的Ta-t,Ta-b,Tb, M和B型病毒粒子。方差分析表明,5组病毒粒子间长度差异极显著,即组Ⅰ<组Ⅱ<组Ⅲ<组Ⅳ<组Ⅴ;病毒粒子宽度差异也极显著,但仅组Ⅰ粒子的宽度明显大于组Ⅳ 和组Ⅲ,说明在没有病毒RNA参与的情况下,单由不含病毒RNA的外壳蛋白亚基所构成的粒子其横向结构较为松散。对AMV统计分析的结果与前人根据对病毒粒子结晶中典型的粒子进行X射线衍射分析或计算机模拟所获得的结果基本吻合,但组Ⅴ粒子,即最长一组AMV病毒粒子的统计长度明显小于结晶中X-射线衍射分析所测得最长的B型粒子。     

Genetic variation in a Norwegian germplasm collection of white clover (Trifolium repens L.)

Phenotypic (r_p), genotypic (r_g), genotype × location (r_gl) and error (r_e)correlations for important agronomic characters were estimated for eleven Norwegian populations of white clover (Trifolium repens L.), originating from between 58^°52′N and 69^°30′N latitude, and from altitudes of 10 to 450 m a.s.l. The populations were evaluated in monoculture clonal field plots for two years at two locations in Norway. All pairwise correlations between foliage height, leaflet length, dry matter yield (DMY) and general performance were positive and significant. Winter survival was positively correlated with general performance, spring growth and DMY, but negatively associated with internode length, while seed yield showed a small positive genotypic correlation with foliage height. Considerable differences were, however, revealed among populations with regard to sign and magnitude of the estimated correlations. Within-population estimates of r_g were consistently positive between DMY, general performance and most other characters; between foliage height on the one hand and leaflet length, winter survival and seed yield on the other hand, and between internode length and leaflet length, indicating pleiotropy. Correlations involving other character-combinations varied substantially among populations, and imply presence of linkage and/or coadaptation. Path coefficient analysis was used to partition the genotypic correlations between some of the characters into direct and indirect effects. Path coefficients revealed that foliage height had the highest positive direct effect on DMY, followed by winter survival and internode length. Leaflet length, which showed a positive, significant simple correlation with DMY, exhibited a negligible direct influence, counterbalanced nearly completely by the positive indirect effect on DMY via foliage height. Positive indirect effects on DMY via foliage height were also found for winter survival and internode length. The coastal populations from North and Middle Norway, and a southern highland population showed the largest expected responses to phenotypic selection for most of the characters. The results demonstrate that there is enough genetic variation in adapted local populations to develop new improved cultivars adapted to high-latitude environments that combine upright growth habit with sufficient winter-hardiness and persistency. This revised version was published online in July 2006 with corrections to the Cover Date.     

Nitrogen Fixation in Hybrids of White Clover (Trifolium repens L.) and Caucasian Clover (Trifolium ambiguum M. Bieb)

Hybrids between white clover (Trifolium repens L.) and Caucasian clover (or Kura clover, Trifolium ambiguum M. Bieb) are a potential route for the improvement of drought tolerance and persistence in white clover. However, to be agronomically viable they must show no significant reduction in their potential for nitrogen fixation relative to white clover. A comparative study of growth rate and nitrogen fixation was carried out in flowing solution culture without a supply of mineral nitrogen to the plants. The two parental species and two generations of backcross hybrids, with white clover as the recurrent parent, were assessed. The growth rate and N content of T. ambiguum were significantly lower than those of the other lines. However, dry matter production, nodule biomass per plant and rates of fixation were similar in second‐generation backcross plants and white clover. The results suggest that the agronomic potential of this novel germplasm is not compromised by limitations with respect to nitrogen fixation.     

Influence of single applications of nitrogen on white clover nitrogen fixation in autumn and winter dairy pastures in south‐west Victoria,Australia

Abstract

Effects of nitrogen (N) (0, 15, 30, 45 and 60 kg N ha^?1) applied at five different times during autumn and early winter on the N fixation of Trifolium repens L. (white clover) in Lolium perenne L. (perennial ryegrass) / white clover pastures were examined (Experiment 1). Effects of applying different N fertilisers (e.g. urea and ammonium nitrate) at 45 kg N ha^?1 in autumn, with and without phosphorus (P), potassium (K) and sulphur (S) on N fixation were also tested (Experiment 2). In Experiment 1, percentage N derived from the atmosphere (percent Ndfa) by white clover varied between 87% and 91% in the period after (24 to 36 days) N application. Increasing rates of N and time of application did not influence percent Ndfa. The amount of N fixed by white clover ranged from 0.8 to 3.7 kg N ha^?1 in the period after N application. Increasing rates of applied N produced a significant (P<0.05) linear increase in the amount of N fixed. In Experiment 2, percent Ndfa and amount of N fixed (1.9 to 4.1 kg N ha^?1) were unaffected by different N fertilisers, with and without P, K and S, in the period after (37 days) fertiliser application. For both experiments, fertiliser N increased dry matter yield while having no effect on white clover composition. It is concluded that single applications of N during the autumn and early winter benefit pasture growth without adversely affecting white clover N fixation or clover composition. This finding, however, will require further investigation.     

岷山红三叶总异黄酮提取方法的研究

为选择提取岷山红三叶中总异黄酮的最佳方法,本文研究了用回流法、冷浸法和索式提取法提取岷山红三叶中总异黄酮的效果.通过紫外分光光度法测定提取液中的总黄酮含量,结果表明:回流提取法提取效果优于冷浸法和索式提取法.具有安全、简便和提取率高的优点.     

土壤速效磷浓度对白三叶构型及能量分配的影响

土壤速效磷浓度对白三叶地上部的垂直分布影响显著。结果表明,白三叶构件密度、分枝密度、分枝角度及总能量均与土壤速效磷浓度呈极显著正相关,节间长度则与之呈极显著负相关。叶片和匍匐茎的能量与土壤速效磷浓度呈正比。花序的能量则随着有效磷浓度的增加而减少。茎能量分配随着有效磷浓度的增加呈铃形曲线型变化。     

西南地区野生马蹄金无性繁殖特性研究

采用野生马蹄金Dichondra repens（SD200310、SD200411、GD200504、SD200304）为材料,研究了无性系构件克隆生长的时间动态、形态、空间构型等。结果表明：1）主茎增长率随时间推移而下降,空间扩展依赖源株和早生分株、叶片的贡献;2）移植植株生长和茎叶扩展之间对物质能量的需求变换,导致了无性系的生长格局及无性系构件和生物量在空间上的分配与配置差异;3）以5 cm×5 cm草皮间铺栽植在密度为D2（40 cm×40 cm）时,主茎长（22.33 cm）、叶片数（28.38片）、节数（24.76节）和节长（1.42 cm）的均值达最大值,呈最佳生长状态,为合理的建植密度;4）随密度增加,间隔子长度递减,分枝角度增加,分枝强度减小,体现了在密度影响下的可塑性变化。     

PEG模拟干旱胁迫下29份偃麦草种质种子萌发期抗旱性评价

以20%聚乙二醇溶液(PEG-6000)为渗透介质模拟干旱胁迫条件,对29份偃麦草种质资源进行了种子萌发期抗旱性评价。结果表明:PEG胁迫降低了偃麦草种质资源的发芽率、发芽势、发芽指数、活力指数,抑制了胚芽和胚根的生长发育。以相对发芽率、相对胚根长、相对胚芽长、萌发抗旱指数、胁迫指数、相对发芽势及相对活力指数为依据,通过隶属函数法综合评价认为,29份偃麦草种质资源的抗旱性顺序依次为:E39E14E11E13E16E03E07E25E34E42E09E29E17E31E21E26E06E10E12E27E38E08E01E04E41E19E37E02E24。     

偃麦草种质资源遗传多样性的RAPD分析

通过对DNA提取方法及RAPD反应体系进行探讨,建立了适应偃麦草基因组DNA提取的方法及优化的RAPD反应体系。在此基础上,依据Jaccard相似系数,采用UPGMA方法进行聚类,判定32份偃麦草种质材料间的亲缘关系及遗传多样性。结果表明:(1)改良常规CTAB法,即对样品先进行洗涤并提高CTAB含量到3%可提高偃麦草DNA的提取质量。(2)对100条随机引物进行筛选,共筛选出18条多态性高、重复性好的随机引物,以此对32份材料进行PCR扩增,共扩增出264条带,多态性条带为93.7%。(3)以遗传相似系数为依据,对32份偃麦草材料进行聚类分析,在相似系数为0.373处可将供试偃麦草种质资源划分为5大类群。     

紫茎泽兰浸提液对牧草种子发芽和幼苗生长的影响

紫茎泽兰被我国列为16种有害外侵物种之首,在西南地区大规模侵入草场、农田、森林,很有必要了解其化感效应,研发无害化处理与资源化利用相结合的技术。试验以广泛分布于四川省凉山州的白三叶、黑麦草和紫花苜蓿为材料,比较了新鲜(extract of fresh E. adenophorum, EFA)和腐熟紫茎泽兰的浸提液(extract of composed E. adenophorum, ECA)对牧草种子萌发和幼苗生长的影响,以明确这种外侵植物对草场植被的危害作用和腐熟处理效果。随EFA浸种和培养浓度的提高,不同程度地抑制牧草种子发芽和幼苗生长。当浓度达到100 mg/L EFA时,牧草根毛消失,根尖向上卷曲,离开EFA,根尖发黑,甚至死亡。相反,用铜绿假单胞菌(Pseudomonas putita sp.)和高温纤维菌(Clostridium thermocellum sp.)组成的混合菌剂腐熟紫茎泽兰后,ECA提高牧草种子发芽率、发芽指数和活力指数,并促进幼苗生长,其最大增幅达到21.11%(种子发芽率),24.12%(苗高)和22.48%(生物量)。此外,用100 mg/L EFA浸种和培养牧草幼苗,抑制胚乳中的淀粉、蛋白质和肌醇磷酸盐水解,显著降低游离氨基酸、可溶性糖、可溶性磷,以及幼苗中的叶绿素、根系活力及硝酸还原酶活性,ECA则相反。这可能是EFA抑制(或ECA促进)牧草种子发芽和幼苗生长的重要生理原因之一。因此,EFA含有对牧草有害化感的物质,抑制其种子发芽和幼苗生长;腐熟紫茎泽兰可降解毒素,刺激牧草种子发芽,促进幼苗生长,实现紫茎泽兰的无害化处理与资源化利用,为当地农业和畜牧业生产提供大量的优质有机肥源。