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.     

Effects of Competition upon the Productivity of White Clover-Perennial Ryegrass Mixtures. Analysis of and Interrelations between Characters

A diallel crossing programme amongst tour contrasting white clover varieties was used to generate material for studying the interrelationships amongst those characters which affect the productivity of white clover- perennial ryegrass mixtures under a cutting-only management regime. Such a regime favoured clover growth. All the clover characters exhibited strong positive correlations with mixture yield. However, this combination of clover characters did not promote growth of the grass companion. For this a low growing variety with a dense stolon network appeared preferable. Path analysis indicated that differences existed between the two companion grass varieties used for this experiment in their upon clover characters.     

Effects of Competition upon the Productivity of White Clover-Perennial Ryegrass Mixtures. Seasonal Trends

Seasonal trends among those characters, affecting productivity in white clover-perennial ryegrass mixtures were investigated m a set of 20 mixtures using clover material derived from a. diallel cross between four contrasting white clover varieties. The productivity and associated vegetative characters showed the familiar pattern of high grass production in spring, and early summer, with a secondary peak of growth in autumn, whilst clover achieved its; highest productivity levels in mid-summer. A significant linear relationship was established between clover canopy height and ryegrass canopy height for all 20 mixtures. Although no significant heterogeneity was detected among the fitted regression lines, there was an indication that the linear regressions provided a better fit to the data in those mixtures having ‘Skomer’ as the grass companion. An analysis of the differences in canopy height between ryegrass and clover indicated that the ‘Menna ‘/’S. 23’ mixture had a reduced seasonal range compared to the other mixtures. Consequently, during the early par', of the growing season, when the tallest canopies occurred and. when shading of clover by the grass was most intense, the difference in canopy height between ‘S. 23’ and ‘Menna’ was relatively low. There was a pronounced effect of grass companion upon canopy height difference, due entirely to the taller growth habit of the ‘Skomer’ ryegrass variety, These interrelationships are discussed briefly in the context of improving the productivity of white clover-perennial ryegrass mixtures.     

Use of molecular marker diversity to increase forage yield in timothy (Phleum pratense L.)

Molecular marker technologies may provide a tool to overcome the forage yield plateau in timothy (Phleum pratense L.). Therefore, a study was designed to investigate the relationship between marker‐based genetic distance (GD) estimates and yield. Genetic distances were estimated using Dice coefficients framed by 28 simple sequence repeat markers. In Experiment 1, parents with high general combining ability (GCA) from two contrasting first‐generation synthetic strains (exhibiting high and low yields) were compared. Average GDs of each strain were 0.74 (high) and 0.68 (low). These differences indicated that GD may be partially the basis for contrasting yields. In Experiment 2, GDs among 40 parents of a polycross were used for calculating general genetic distance (GGD), which is indicative of their allelic complementation. Analyses revealed a significant (P < 0.01) moderate correlation (r) between GGD and GCA for yield (r = 0.45) and a significant (P < 0.01) residual mean square for the regression of yield on GGD, suggesting that considerable non‐additive effects were associated with GCA. The results are indicative of the potential use of GD estimation for yield improvement in timothy.     

Effects of Competition upon the Productivity of White Clover-Perennial Ryegrass Mixtures. Genetic Analysis

A diallel cross amongst four contrasting white clover varieties was used to provide genetic information on those characters which affect the productivity of white clover-perennial ryegrass mixtures when grown under a cutting-only management regime. Generally speaking those characters recorded on the clover families and in mixtures exhibited highly significant additive and non-ad dative genetic effects, though for1 sortie characters the latter could not be ascribed solely to dominance effects. For two of the clover characters, stolon and leaf number, the genetic picture was radically altered in mixtures by the effects of inter-specific competition Pseudo-genetic effects were also detected for the grass characters, bur it was suggested that the two ryegrass varieties used here were exhibiting phenotypic plasticity. As a group the four intra-varietal crosses performed significantly better than the six intra-varietal crosses for all clover and mixture characters. Only one of the inter-varietal crosses had significantly positive specific combining ability effects for most characters and that was between the two long established varieties ‘S. 184’ and ‘S. 100’. The implications of these results for the breeding of white clover varieties for use in mixtures are briefly discussed.     

2种草本植物对三裂叶蟛蜞菊化感物质胁迫的响应

为了研究黑麦草（Lolium perenne）和草地早熟禾（Poa pretensis）对三裂叶蟛蜞菊（Wedelia trilobata）化感物质胁迫的响应机制,以不同浓度的三裂叶蟛蜞菊提取液处理了这2种植物的种子和幼苗,比较了种子萌发和幼苗生长指标。结果表明：当提取液浓度为0.01 g/mL时,黑麦草种子的发芽率、发芽势和发芽指标未受影响,而草地早熟禾种子的这3项值均升高,之后随着提取液浓度的增加这2种植物种子的3项值都逐渐降低;随着提取液浓度的增加,黑麦草幼苗胚根长较草地早熟禾降低更迅速,2种植物产生1个和2个次生根的幼苗数逐渐减少,黑麦草幼苗胚芽长呈先升高后降低的趋势,草地早熟禾幼苗胚芽长却呈逐渐降低的趋势。草地早熟禾以提高发芽率、发芽势和发芽指标对低度三裂叶蟛蜞菊化感物质胁迫作出适应性反应,黑麦草却以胚芽的补偿性生长对这种低度胁迫作出适应性反应。     

温度对西藏5种野生豆科牧草种子萌发的影响研究

为探明毛果胡卢巴、劲直黄芪、天蓝苜蓿、镰荚棘豆和窄叶野豌豆5种野生豆科牧草种子萌发的适宜温度以提高其萌发率,研究了0/10℃ 、5/15℃ 、10/20℃ 、15/25℃ 、20/30℃ 、25/35℃ 、30/40℃等7种发芽温度对西藏5种野生豆科牧草种子萌发的影响.结果表明,5种野生豆科牧草种子在0/10℃条件下均无萌发;发芽率、发芽势、发芽指数和活力指数等指标随昼夜温度的升高呈先上升后下降趋势;毛果胡卢巴、劲直黄芪、天蓝苜蓿、镰荚棘豆和窄叶野豌豆牧草在适宜温度范围内种子萌发时滞最短,依次为2,2,2,3,4d;毛果胡卢巴和镰荚棘豆种子萌发最适温度为15/25℃,发芽率分别高达95%和812.5%;劲直黄芪、天蓝苜蓿、窄叶野豌豆种子萌发最适温度为20/30℃,发芽率依次为85%、912.5%和65%.     

Yield and Persistence from Mixtures of a Winter Hardy and a Verticillium Wilt Resistant Lucerne Cultivar

In British Columbia, Lucerne stand persistence is reduced by inadequate disease resistance, winter hardiness, or both. We evaluated the possibility that persistence could be improved by sowing mixtures of winter hardy and verticillium wilt (VW) resistant cultivars. Our hypothesis was that dry matter yield of mixtures of two Lucerne cultivars could be calculated simply from the proportion of each cultivar in the mixture and their yield in pure stand. A winter hardy cultivar, Beaver, was grown in mixtures with each of three VW (caused by Verticillium albo-atrum Reinke & Berthier) resistant cultivars (WL316, Sparta, or Barrier) in proportions of 0, 0.25, 0.5, 0.75, and 1.0. The yield of a mixture of two cultivars could be calculated from the proportion of each cultivar in the seed mixture and their yields in monoculture. In the absence of a winter where severe injury to Lucerne stands occurred, the VW-resistant cultivar Barrier yielded about 2 t ha⁻¹ year⁻¹ more than the more winter hardy Beaver.     

Effects of water deficit and plant interaction on morphological growth parameters and yield of white clover (Trifolium repens L.) and ryegrass (Lolium perenne L.) mixtures

The effects of soil water deficit and interspecific plant interaction were studied on the dry matter (DM) yield of white clover and ryegrass and on the morphogenesis of white clover. Plants were grown either: (1) individually (no interaction); or in a mixture of equal plant numbers with either (2) just shoot interaction, or (3) both shoot+root interaction. Plants were subjected to soil water deficits corresponding to no (0 MPa), moderate (−0.5 MPa) or severe (−1.0 MPa) water deficit. Ryegrass had higher above- and below-ground DM yields than white clover. The above- and below-ground DM yield for ryegrass, and the above-ground DM yield, stolon growth and relative growth rate (RGR), and leaf appearance rate (LAR) for white clover decreased as soil water deficit increased. In shoot+root interaction at no and moderate soil water deficit levels, white clover had the highest proportion of above-ground growth in the leaf form (69%) and had, respectively, 11% and 32% more above-ground DM yield than when grown in just shoot interaction; ryegrass had, respectively, 20% and 25% more above-ground DM yield than ryegrass grown in just shoot interaction. In shoot+root interaction at severe soil water deficit, ryegrass had twice as much above-ground DM yield as white clover (3.50 g per plant versus 1.59 g per plant, respectively) and white clover had 60% less above-ground DM yield than when grown in just shoot interaction. In a soil column of restricted depth (30 cm) at no and moderate soil water deficit levels, remarkable increases in shoot biomass yield were observed for both white clover and ryegrass grown in shoot+root interaction. The increased shoot biomass yield of ryegrass can be attributed to benefits from white clover's N fixing ability, whereas the causes for increased white clover biomass yield need to be studied further. However, at severe soil water deficit, ryegrass had a competitive advantage over white clover when grown in shoot+root interaction. This was due to the larger root system of ryegrass and its ability to control transpirational losses more efficiently, thus prolonging its growth period compared with white clover.     

The Effect of Isozyme Selection on Yield and Flowering Time in Lolium perenne

A series of lines, differing in isozyme genotype, were constructed by selection from within three cultivars of Lolium perenne. Field assessment of the progeny of these selected line? revealed variation in yield and timing of inflorescence emergence. This variation between lines from within a cultivar could not be accounted for by the differing levels of homozygosity attained. In some instances differences in yield were associated with homozygosity for specific alleles at the PGI/2 locus, background genotype was however, of major importance. The variation identified could be attributable to founder effects or possible linkage of quantitative trail loci to the PGI/2 locus.     

Effects of Interspecific Competition on the Inheritance of Quantitative Traits in White Clover *)

Analysis of a half diallel cross among four white clover cultivars, grown as monocultures and in mixtures (duocultures) with two separate perennial rye-grass cultivars, confirmed that for stolon and leaf number a higher proportion of the genetic variance in duocultures was non-additive. For canopy height and dry weight, however, this proportion was less affected by inter-specific competition. An additive-dominance model of gene action sufficed for all four characters in monocultures, but in duocultures epis-tasis was just one of the factors complicating the genetic picture. This, coupled with short-term reversals in the direction of dominance, merely illustrates the complexity of breeding white clover cultivars. Possible future developments in the breeding of white clover are discussed in the light of these results.     

Genetics and biology of cytoplasmic male sterility and its applications in forage and turf grass breeding

Hybrid breeding can exploit heterosis and thus offers opportunities to maximize yield, quality and resistance traits in crop species. Cytoplasmic male sterility (CMS) is a widely applied tool for efficient hybrid seed production. Encoded in the mitochondrial genome, CMS is maternally inherited, and thus, it can be challenging to apply in breeding schemes of allogamous self‐incompatible plant species, such as perennial ryegrass. Starting with a general introduction to the origin and the function of mitochondria in plants, this review focuses on the genetics and biology of CMS systems in plants to identify conserved and system‐specific mechanisms. We examine prospects of comparative mitochondrial genomics to identify candidate genes and causative polymorphisms associated with CMS across species and discuss specificities, obstacles and potentials of CMS as a breeding tool for maximizing heterosis in forage grasses. The purpose of the review is to highlight the importance of CMS and hybrid breeding in grasses, with the aim of facilitating research and development of novel breeding strategies to address the future needs for food, feed and biomass production.     

Comparison and integration of genetic maps generated from F2 and BC1-type mapping populations in perennial ryegrass

Linkage maps of perennial ryegrass were constructed from F₂ and BC₁‐type populations using, predominantly, restriction fragment length polymorphism data based on heterologous probes used in mapping other grass species. The maps identified seven linkage groups, which covered a total of 515 cM (F₂) and 565 cM (BC₁). They were aligned using 38 loci identified in both populations (common loci) and a possible marker order for all mapped loci in either population was identified in an integrated map. The estimated recombination frequencies and map distances between adjacent common loci were compared between the two data sets and regions of heterogeneity identified. Overall, the common markers identified a map distance of 446 cM in the F₂ population and 327 cM in the BC₁ population, reflecting a higher recombination frequency in the former, although the difference was not evenly spread over the seven linkage groups.     

Heritability of, and genetic correlations among, forage and seed yield traits in Ladino white clover

Sixteen white clover genotypes and their half-sib progenies were grown in pure stand. Each clover progeny was also grown in a mixed stand that also included three grass varieties of different species. Dry matter (DM) yield was measured over 2 years and seed yield at the second year. Competitive ability of clover families was defined as the ratio between mixed stand and pure stand for clover DM yield. Narrow-sense heritability from parent-offspring regression of pure stand data was high to moderate (h²0.50) for DM yield, seed yield and most of their components. Persistence as predicted by stolon density showed negative genetic correlations with seed yield (r_g= -0.70) and DM yield (r₂= -0.60), whereas seed yield and DM yield tended towards a negative correlation (r₂=0.45). Sizes of different vegetative or reproductive organs were generally correlated positively. Evidence was provided that the set of parent genotypes represents well the genetic variation available within the Ladino gene pool. The results highlighted the difficulty of combining relatively short-term DM yield, persistence and seed yield into a unique plant type. Differences in competitive ability emerged only in the second year, better ability being related mainly to petiole length among the traits assessed in pure stand.     

北方冬麦区小麦产量潜力及增产技术研究进展

为了合理、准确地分析北方冬麦区的小麦产量潜力,找到限制因素,探寻相应的调控技术,提高小麦生产力。归纳了本地区模型模拟的冬小麦产量和高产记录,比较分析了模型模拟和高产纪录产量水平的差异,总结了限制小麦产量差缩小的主要原因与可能的调控技术。得出当前模型模拟结果低于高产记录是因为数据采集年份和数据量的影响;产量性能理论是定量化分析产量差异原因的有效方法;指出北方冬麦区限制小麦产量差缩小的主要原因和调控技术。认为小麦产量提升应从产量差确定、产量性能分析、集成技术等3个方面依次开展。     

脱驯化对寒地冬小麦抗寒性影响的探析

寒地冬小麦的安全越冬受制于 3个外界因素, 分别是低温驯化程度、 越冬期间温度、 以及返青期温度。为分析低温驯化对冬小麦抗寒性的影响, 笔者以抗寒性不同的 2个冬小麦品种为材料, 在其生长的低温驯化阶段分别对其进行脱驯化及低温处理, 测定不同处理下冬小麦植株的成活率及保护酶活性。研究结果得出, 10℃脱驯化处理 2天对植株造成的伤害较 20℃脱驯化 2天显著降低; 抗寒品种 ‘东农冬麦 1号’ 只有在 11月 10日发生 10℃脱驯化 2天其成活率显著降低, 而不抗寒品种在 10月 26日发生10℃脱驯化 2天其成活率为 50%; 20℃脱驯化 2天再-12℃ 3天处理, 抗寒品种在 10月 31日后其成活率低于 50%, 相同处理下不抗寒品种所有时期成活率均低于 50%。抗寒品种经历 20℃脱驯化 2 天后再经历-12℃ 1天低温植株的 SOD酶活性达到最高。由此得出, 低温驯化期发生脱驯化冬小麦植株的成活率降低。     

Influence of recurrent selection for flowering on flowering and yields in kura clover

Summary These investigations were conducted to determine the effectiveness of first- and second-season selection programs for increasing forage and seed yield in kura clover (Trifolium ambiguum Bieb.).Rhizo kura clover, the base population, was grown as spaced plants in two programs for six generations of selection for flowering in the seedling and second seasons. Remnant seed for each generation of selection was used to establish spaced plant and broadcast evaluation trials.The first-season selection program was effective in increasing flowering not only in the first season, but for two subsequent seasons. The second-season selection for flowering had little or no effect. However, vigor, forage and seed yields were not increased by either program, and the first-season program progressively reduced vigor and forage yields as generations of selection increased. The cause of this is unknown but may be associated with inbreeding depression or detrimental physiological effects of first-season flowering. Reselection to eliminate possible inbreeding effects is being conducted to further examine the possibility of increasing seedling and aftermath vigor in kura clover.     

不同种植密度对寒地水稻浅土层热效应的影响

为了提高人们对寒地水稻浅土层热效应特征变化的认知度。试验在大田条件下,以‘空育131’为试验材料,设置行株距30×8 cm (D₁)、30×10 cm (D₂)、30×12 cm (D₃)、30×14 cm (D₄)、30×16 cm (D₅) 5个密度水平,分析不同种植密度对浅土层热效应的影响。结果表明,各土层温度在抽穗期达最高值,灌浆后开始下降,且温差缩小,其中以10 cm土层温度稳定性最高。受种植密度影响,高密度处理下土温白天增温快,夜间最低,昼夜温差大,最高日平均温度出现的早,其中D₁、D₂处理在10 cm、15 cm土温变化上几乎同步。相比之下,各土层T_max、T_min出现时间随土层的加深而向后推迟,生育期内T_avg、T_max、T_min与气温极显著正相关,而T_max-_min则随密度的增加有减小的趋势,主要表现在分蘖期和成熟期,且作用效果随密度增加而增大。产量以D₂处理最高,表现为9.27 t/hm ²,较D₁、D₅处理增幅13.5%~14.6%。说明适宜密度条件能够实现对浅土层热效应的科学调控,并获得产量的提高。     

Effect of generation of inbreeding, cutting treatment and year on agronomic traits in berseem populations

The selfing effect in berseem clover (Trifolium alexandrinum L.) was analysed by comparing generation means for nine agronomic traits (dry matter yield, plant height, leaf-stem ratio, harvest index, seed yield and its components). Parents, S₁, S₂, S₃, and S₄ generations of six populations of different geographical origin (3 from Egypt and 3 from southern Italy) were investigated to estimate the relative changes with increasing homozygosity and to prove the effectiveness of selfing in a breeding program. The experiment was carried out at Foggia (Italy) under field conditions for two years (1995 and 1996) adopting two cutting treatments: at fifth internode elongation (A) and flowering (B). The mean values decreased with the advancement in selfing generations in both years and cutting treatments for the most of the traits. Treatment B yielded more biomass and seed yield than treatment A in both years. Cutting treatments did not affect the adaptability of the selfed progenies of populations with different geographical origin, in fact, the Italian populations were more productive for dry matter under both cutting treatments (856.6 g m^-2 on average), whereas Egyptian populations proved superior for seed yield particularly under treatment B (62.5 g m^-2 on average). Inbreeding depression was greater for forage dry matter and seed yield (−62and −79% on average, respectively), whereas the plant height and 1000-seed weight were the least susceptible traits (−26 and −19% on average, respectively). Estimates of the parameters of the stability analysis showed that not all populations responded to inbreeding level and environment variations to the same degree. Differences were evident under treatment A, only. Development of self-fertile, relatively vigorous inbred lines of berseem clover with different degrees of homozygosity appears possible. Genotypes tolerant to selfing from Egyptian and Italian groups have been obtained by inbreeding and selection for self-fertility; they could be utilised as basis for producing new breeding activities. This revised version was published online in July 2006 with corrections to the Cover Date.     

Performance of S2 Winter Barley Progenies from Original and Improved Populations Developed via Recurrent Selection

The effect of recurrent selection procedure for improving grain yield in autogamous cereals was evaluated in a six-rowed winter barley population. Gain from selection was estimated by field testing 90 random S2 lines from each of the C₀, C₁ and C₂ populations. Response to selection for grain yield was 0.78 t/ha from C₀ to C₁ and 1.09 t/ha from C₁ to C₂. Broad-sense heritability and genotypic variance for grain yield remained high in all cycles which suggests further gain from additional selection cycles. Yield increase was due to a higher number of seeds/m2. Significant differences among mean values were observed for heading date (189 days in C₀ and 182 days in C₂), whereas no variation was seen for plant height and 1000-kernel weight. The proposed recurrent selection procedure appears effective to improve the population and to extract superior genotypes for varietal development.