A non-invasive crop ideotype to reduce invasive potential

Summary In plant breeding programs, qualitative and quantitative traits confer market value and, thus, constitute the basis for developing breeding criteria during crop domestication. Some traits such as high male/female fertility are advantageous in the wild and could enable the evolution of cultivated crops into invasive weeds. Other traits, e.g. sterility, are not expected to confer invasiveness. To date there has been very limited involvement in invasion risk assessment by plant breeders. Thus, in this paper we propose that trait-based selection of potential crop species be coupled with species design in the creation of a “non-invasive crop ideotype” as an avenue to reduce invasiveness during domestication. The non-invasive crop ideotype embodies the ideal characteristics for a crop to excel in cultivated environment(s) but minimizes the likelihood it will establish and spread in non-cultivated environments, constituting the underlying foundation for all breeding objectives, choice(s) of breeding methodologies, and propagation techniques for non-invasive crop release. Using ornamental (floriculture) horticultural crops as an example, we identify 10 traits to be used individually or in combination to reduce invasiveness while retaining commercial value: reduced genetic variation in propagules, slowed growth rates, non-flowering, elimination of asexual propagules, lack of pollinator rewards, non-shattering seed, non-fleshy fruits, lack of seed germination, sterility, and programmed death (apotopsis). A non-invasive crop ideotype would constitute the underlying foundation for all breeding objectives, the choice(s) of breeding methodologies, and propagation technique(s). The ideotype should be flexible and should adjust to species- and crop-specific traits to account for the intended use. For example, development of sterile cultivars may have negligible effects in reducing invasiveness if the crops spread vegetatively. A non-invasive crop ideotype may increase the direct participation of plant breeders, who are the professionals directly involved in the collection, development and release of new crops, in reducing the invasive potential of ornamental crops. Future research is required to determine the feasibility of incorporating each trait into various crops, use of classical or molecular techniques for creation of non-invasive crops, trait stability (lack of genotype × environment interaction over years and locations), consumer acceptance, and long-term viability.     

Allelopathic Effect of Eucalyptus globulus Labill. on Cyperus rotundus L. and Cynodon dactylon L. Pers.

The allelopathic potential of Eucalyptus globulus Labill. (gum tree) fresh and dried leaf leachates was studied using two perennial weeds, viz. purple nutsedge (Cyperus rotundus L.) and bermuda grass (Cynodon dactylon L. Pers) as test weeds. Aqueous leachate of fresh leaves of eucalyptus significantly suppressed the establishment of vegetative propagules and early seedling growth of the weeds. Leachate of fresh leaf cuttings had growth inhibitory effect on bermuda grass but showed growth promotion effect on purple nutsedge. Similarly the leachate of dried leaves of eucalyptus had differential influence on the growth of the two weeds. There is a possibility to harness the allelochemicals of eucalyptus leaves as herbicides for the management of these perennial weeds.     

椴树属树种种子休眠原因及提高种子萌发率概述

椴树属（Tilia L.）树种种子普遍具有休眠特性,给育苗生产带来了一定的困难,破除其休眠及提高种子萌发率的研究,对该物种种质的保存及可持续利用等具有重要意义。笔者从被覆物的存在、抑制物质的存在、胚的发育状况对椴树属树种种子休眠原因的研究进展进行综述,针对其休眠特性,指出提高其萌发率方法有层积处理、化学物质处理、胚的培养等,以期为椴树属树种种子休眠解除进一步研究,及椴树属树种产业的健康可持续发展的科学合理利用提供参考。     

Light competition for invasive species control: A model of cover crop–weed competition and implications for Phalaris arundinacea control in sedge meadow wetlands

Summary Since resource competition plays a critical role in many plant invasions, controlling invasive vegetation may require managing the supply of limiting resources. For example, lowering light availability with a cover crop might prevent invasions during community establishment in light-limited restored ecosystems. However, most cover crops evaluated for invasive species control either do not adequately suppress invasives or equally suppress desired species. To improve our ability to predict cover crop effectiveness, we use a theoretical model of plant competition to identify potential mechanisms by which cover crops might favor desired species over invasives. In addition, we consider the model's implications for controlling an invasive forage, Phalaris arundinacea, in restored sedge meadows. The model suggests that cover crops will improve the outcome of competition between desired and invasive species only when (1) desired species have lower minimum light requirements than invasive species and (2) invasive species dominance results from rapid establishment and resource preemption. Cover crops in the model favor desired species over faster-growing invasives because faster-growing invasives are positioned higher in the canopy. Invasive species higher in the canopy shade desired species more than desired species shade invasives. Consequently, by reducing invasive species biomass, cover crops give desired species a competitive advantage. The simple requirements for cover crop success in the model suggest that cover crops may be effective for invasive species control in light-limited restored ecosystems. The available information on P. arundinacea responses to shade suggests, however, that cover crops are unlikely to favor sedge meadow species over P. arundinacea.     

玉米光周期敏感相关性状发育动态QTL定位

玉米是短日照作物,大多数热带种质对光周期非常敏感。光周期敏感性限制了温、热地区间的种质交流。研究玉米光周期敏感性的分子机理,有利于玉米种质的扩增、改良、创新,提高玉米品种对不同光周期变化的适应性。本研究以对光周期钝感的温带自交系黄早四和对光周期敏感的热带自交系CML288为亲本配置的组合衍生的一套207个重组自交系为材料,在长日照环境条件下对不同发育时期的叶片数、株(苗)高变化进行QTL分析。结果表明,双亲间的最终可见叶片数和株高差异很大;发育初期CML288的叶片数和苗高都低于黄早四,而发育后期CML288的叶片数和株高都明显高于黄早四;测定各时期F₇重组自交系间也存在显著差异。利用包含237个SSR标记、图谱总长度1 753.6 cM、平均图距7.40 cM的遗传连锁图谱,采用复合区间作图法,分别检测到控制叶片数和株(苗)高发育的QTL 11个和20个。但是,没有一个条件QTL 能在测定的几个时期都有效应。在长日照条件下,控制叶片数与株(苗)高的非条件与条件QTL主要集中在第1、9和10染色体上,特别是在第10染色体的标记umc1873附近均检测到了影响这两个性状的QTL,且在不同的发育时期单个条件和非条件QTL所解释的表型变异分别为4.34%~25.74%和10.02%~22.57%,表明这一区域可能包含光周期敏感性关键基因。     

Diallel cross analysis of seed germination traits in sugar beet

A diallel cross design, involving six diploid O-type lines and their cytoplasmic male sterile (CMS) equivalents was used to examine the genetic control of characters determining seed viability and vigor of seed and seedling in sugar beet. Six characters including percentage of germination, seedling establishment, weight of 1000 germs, seedling vigor, speed of germination, and monogermity were analyzed. Additive genetic effects were shown to be highly important for all characters and significant dominance effects were found for the percentage of germination and seedling establishment, weight of 1000 germs, and rate of monogerm seeds produced by multigerm plants. There were significant reciprocal variations for most characters, indicating that maternal effects and differences of self-incompatibility mechanisms may influence the expression of some characteristics related to the amount of viable seeds produced in plant. Variance of genotypes for seedling vigor and speed of germination was nonsignificant, indicating that both characters are mainly affected by environmental factors. The relative importance of heritability estimates and the ratio of GCA, SCA, and environmental variances to phenotypic variances were calculated for all the traits examined. It is suggested that seed traits are as important as root quality traits for the development of sugar beet varieties. This revised version was published online in August 2006 with corrections to the Cover Date.     

种子休眠与萌发综述

种子休眠是高等植物中显花植物(即裸子植物和被子植物)经过长期进化而获得的一种对环境条件及季节性变化的生物学适应。休眠的种子可以在不适宜幼苗生长的情况下阻止种子的萌发,减少子代在恶劣环境萌发的的风险,一定程度上保障了种群的延续。本综述重点介绍种子休眠的类型、外界环境因素与母体环境因素以及植物激素对种子休眠与萌发的影响,并介绍了休眠的进化,各种不同类型的休眠在系统发生树上的分布,以期在阐明种子休眠机制的基础上提出一些解决生产过程中种子休眠问题的方法与路径,并为破坏严重的野生植物资源的保护,引种栽培提供理论依据。     

Quantitative trait locus analysis of seed germination,seedling vigour and seedling‐regulated hormones in Brassica napus

Good germination and seedling vigour are major breeding targets in winter oilseed rape (Brassica napus), because seedling vigour and prewinter crop establishment are closely associated with postwinter growth and yield. Here, we identified quantitative trait loci (QTL) related to germination, seedling vigour and seedling‐regulated hormones in a doubled haploid (DH) mapping population from a cross between winter oilseed rape parents with high vigour (Express 617) and low vigour (1012‐98). By phenotyping in a climate‐controlled glasshouse, we identified a total of 13 QTL on nine chromosomes for germination and seedling‐related traits at 7 and 14 days after sowing (DAS), explaining up to 11.2% of the phenotypic variation for seedling vigour. Forty‐seven metabolic QTL on 15 chromosomes were identified for auxin, abscisic acid (ABA) and dihydrophaseic acid (DPA) at 5 and 12 DAS, explaining up to 49.4% of phenotypic variation in seedling hormone composition. Multitrait QTL hot spots contribute to our understanding of the genetics and metabolomics of germination and seeding vigour in B. napus, and represent potential targets to breed high‐vigour cultivars.     

结缕草直播建坪技术综述

结缕草(Zoysia japonica Steud)是中国重要的乡土草种,主要作为草坪草利用,是唯一的种子可国产化的草坪草。在中国,随着破除结缕草种子休眠技术在种子生产中的应用,结缕草种子直播建坪技术在实际运用中越来越广泛。结合结缕草的特性,作者综述了直播建坪的播种时间、播量、破除种子休眠和养护管理等关键技术,为实际运用提供有用参考,进一步推广其在城市绿地和运动场地中的应用     

Heat stress affects vegetative and reproductive performance and trait correlations in tomato (<Emphasis Type="Italic">Solanum lycopersicum</Emphasis>)

High ambient temperature has adverse effects on plant vegetative and reproductive development and reduces crop yield. To better understand the importance of male and female fertility for tomato fruit set ability under high temperature conditions and to test whether heat tolerance levels among and between reproductive and vegetative traits of genotypes correlate with each other, 13 tomato cultivars were subjected to long-term moderate heat (LTMH) or short-term heat shock (STHS), depending on the trait that was evaluated. LTMH caused significant decrease in performance of nearly all reproductive traits, i.e. pollen viability, pollen number, female fertility, seeded-fruit set and flower number per inflorescence, but not in inflorescence number. Considerable variation was found among cultivars, both under control and LTMH conditions. The cultivars Nagcarlang, Saladette and Malintka 101 produced a higher percentage of viable pollen under LTMH. For fruit set under LTMH condition, only cultivars that had been previously reported as being heat-tolerant produced fruits with seeds. STHS negatively affected vegetative traits concerning seedling survival and membrane stability. Correlation analysis revealed relationships between various traits within the control and heat treatments, but not between the two. Under heat stress fruit set was positively correlated with pollen viability, as well as with flower number per inflorescence. However, no significant correlations were found between vegetative and reproductive traits. Our data highlight the prominent role of pollen viability for tomato fertility under LTMH growth conditions. The observed variation in thermotolerance among different cultivars offers the possibility to decipher underlying physiological and genetic mechanisms.     

Effects of Drought and Competition by a Ryegrass Sward on the Seedling Growth of a Range of Grassland Species

In de‐intensified grassland where an increased seedling recruitment is seen as a prerequisite to enhance plant species diversity, establishment success of introduced seeds of wildflower species is often poor. Outshading by the existing sward and dry weather spells when seedlings are at an early stage of development are major reasons for a low seedling establishment. The effects of drought and competition by an existing Lolium perenne sward on the growth of seedlings of seven wildflower species were investigated under standardized environmental conditions. Without competition (control), the relative growth rate of the wildflower seedlings varied between 103 (Tragopogon pratensis) and 184 mg g^?1 day^?1 (Leontodon autumnalis). Species differed in the extent of growth reduction by competition. Compared with the control, reduction of seedling dry weight ranged from 45 % (Trifolium pratense) up to 88 % (Daucus carota). The time range between onset of desiccation and first effects on growth varied between species, with T. pratense showing early and strong growth reduction in contrast to D. carota being least affected. It can be concluded, that those species which maintain a comparatively high growth rate supported by adapted shoot‐root allocation are most promising for establishment in grassland as they can exploit profiles of higher resource availability.     

Identification of natural variants affecting chlorophyll content dynamics during rice seedling development

Seedling vigour is an important characteristic in relation to crop growth and yield. Traits such as photosynthetic capacity and chlorophyll content contribute significantly to seedling establishment at the early growth stage in various crop species, including rice. A diverse panel of 227 rice varieties from several countries was evaluated to determine chlorophyll contents at multiple time points during the seedling stage using a soil–plant analysis development (SPAD) meter, a non‐destructive portable device. Using new statistical approaches, several chromosomal regions associated with variations in chlorophyll content in the third leaf at 13, 16 and 19 days after imbibition were detected. A single nucleotide polymorphism (SNP) cluster on the end of chromosome 11 was significantly associated with the onset of leaf senescence. This region was enriched with genes related to cell death and the stress response. We have identified rice germplasm showing delayed‐senescence phenotypes, these could be suitable donors and genetic resources for breeding, and the use of significant SNP markers associated with these traits could enhance the efficiency of their selection in breeding programmes.     

The importance of population growth, seed dispersal and habitat suitability in determining plant invasiveness

Summary This paper examines the roles of plant demography, seed dispersal ecology and habitat suitability in influencing invasiveness of horticulturally important species. Section one investigates the relative invasiveness of two woody species, Crataegus monogyna and Prunus mahaleb, and concentrates on differences in demographic and dispersal traits. The second section delineates the invasion of two Asparagus spp. and concentrates on differences in seed dispersal ecology. Section three reports the use of a geographical information system analysis to determine whether habitat suitability, seed dispersal or land management is more important in determining threat of invasion by adventive Olea europaea. C. monogyma, P. mahaleb are closely related with similar habits and overlapping home ranges in Europe. Crataegus monogyna is very invasive in northern New South Wales, having spread rapidly and conspicuously throughout the region and elsewhere in southern Australia at rates of 80–120 m yr⁻¹. Prunus mahaleb is far less invasive, being restricted to a small population, which is expanding at 20 m yr⁻¹. Demographic analysis showed that potential growth rates of P. mahaleb (1.713–1.490) are greater than those for C. monogyna (1.138–1.103). Assessment of the seed dispersal ecology of both species revealed that C. monogyna had seeds dispersed by one bird and three mammals over many kilometers. P. mahaleb had seeds dispersed by six birds and four mammals over distances generally < 100 m. The role of humans in introducing both species and the characteristics of seed dispersal are more influential than demography in determining invasiveness. The more invasive Asparagus asparagoides has smaller fruit with a bicoloured display up to 1.5 m above ground. Less invasive A. declinatus has larger, translucent white fruit displayed at heights < 0.5 m above ground. The role of humans has also been important in shaping the course of invasion. Sensitivity analysis confirms that land management practices, which affect Olea europaea seedling establishment and survival, are most important at a landscape scale in determining invasiveness. The main factors determining the difference in invasiveness relate directly to the changing nature of human management of each species and the ecological interactions between the plants and the invaded environment. This research has implications for the prediction and management of biological invasions; emphasizing the importance of seed dispersal and human activities in determining the course of invasions: both of which cannot be readily predicted.     

入侵植物马缨丹不同部位的化感作用研究

马缨丹是马鞭草科中一种入侵性极强的外来植物,现正在我国中南部尤其是华南地区迅速蔓延扩散。本文采用室内生物监测法研究了马缨丹不同部位水浸液的化感效应。结果表明,马缨丹果实、茎干和叶片的水浸液均对一串红种子萌发和生长产生显著的抑制作用,种子的发芽势、萌发率下降,幼芽、幼根生长的长度缩短,芽长、根长抑制指数上升,并且随着浸提液浓度的增加其抑制效应不断增强。马缨丹不同部位水浸液对发芽势的抑制作用大小为叶片＞果实＞茎干,对萌发率、芽长、根长的抑制作用大小为果实＞叶片＞茎干。说明马缨丹具有较强的化感作用,这将有利于提高其种间竞争能力,促进入侵。     

外源赤霉素浸种对茄子种子萌发和植株生长影响的研究

为研究赤霉素（GA3）对打破茄子种子休眠及植株生长的影响,以16份自交系和2份品种为试材,采用GA3处理种子,对不同自交系种子的休眠特性的解除和杂交品种的植株生长的影响进行研究。结果表明16份自交系取种后1个月芽率都较低,最高为25.5%,最低为0%,不同材料间存在极显著差异,说明初收茄子种子普遍存在休眠现象,但休眠深浅程度存在差异;经1000 mg/L GA3处理,所有自交系的芽率、芽势都有明显提高,其中6份芽率达到90%以上,说明GA3对解除茄子种子休眠效果极为显著。室温干燥器存储4个月后除06036和06039 2份亲缘来自中国北方的黑紫茄自交系芽率在低于80%,其他14份材料均在90%以上。利用GA3浸种处理‘农夫长茄’和‘庆丰紫红茄’对不同生长时期的植株、果实性状和产量调查发现,较高浓度GA3(2000 mg/L)对‘庆丰紫红茄’1叶1心期株高有极显著增加,低浓度GA3浸种处理对‘庆丰紫红茄’及不同浓度GA3对‘农夫长茄’的株高促进作用不明显;4叶期后,不同浓度的GA3浸种处理对‘农夫长茄’和‘庆丰紫红茄’植株高度、茎周径、叶片大小的影响差异均不显著,对2个品种的开花期、商品果性状（单果重、果长、果粗、畸形果率）及产量等影响均未达显著差异;且同一浓度浸种4 h与6 h对植株生长、商品果性状和产量的作用效果一致。本研究可为茄子商用种解除休眠提供理论依据。     

Genetic variation in salt tolerance at the seedling stage in an interspecific backcross inbred line population of cultivated tetraploid cotton

Soil salinity reduces cotton growth, yield, and fiber quality and has become a serious problem in the arid southwestern region of the Unites States. Development and planting of salt-tolerant cultivars could ameliorate the deleterious effects. The objective of this study was to assess the genetic variation of salt tolerance and identify salt tolerant genotypes in a backcross inbred line (BIL) population of 142 lines from a cross of Upland (Gossypium hirsutum) × Pima cotton (G. barbadense) at the seedling growth stage. As compared with the non-saline (control) conditions, seedlings under the salinity stress (200 mM NaCl) showed a significant reduction in all the plant growth characteristics measured, as expected. Even though the two parents did not differ in salt response as measured by percent reduction, significant genotype variations in the BIL population were detected for all traits except for leaf number. Based on percent reduction of the traits measured, several BILs were more salt tolerant than both parents. The results indicate that transgressive segregation occurred during the process of backcrossing and selfing even though both parents were not salt tolerant during seedling growth. Coefficients of correlation between all the traits were significantly positive, indicating an association between the traits measured. The estimates of broad-sense heritability were 0.69, 0.46, 0.47, 0.43, and 0.49 for plant height, fresh weight of shoot and root, and dry weight of shoot and root, respectively, indicating that salt tolerance during cotton seedling growth is moderately heritable and environmental variation plays an equally important role. The overall results demonstrate that backcrossing followed by repeated self-pollination is a successful strategy to enhance salt tolerance at the seedling stage by transferring genetic factors from Pima to Upland cotton.     

Varietal Differences in Development of Maize (Zea mays L.) Seedlings on Compacted Soils

Differences among open-pollinated tropical maize ( Zea mays L.) varieties in seedling development and establishment on compacted soils were studied. Soil dry density was used as an index of compaction. Three soil compaction levels and 12 traits associated with development and establishment of maize seedlings were investigated. A control (without compaction) was also included. Varietal differences were observed for most traits measured. Genetic differences for seedling development on compacted soil were detected. Varietal differences contributed about three times the contribution of compaction to total variability in the traits. Better seedling development and performance were obtained in moderately compacted soil than in the control. Shoot length, shoot dry weight and per cent dry matter in roots were good indicators of the tolerance of maize seedlings to compaction. A physiological strategy for maize seedling establishment on compacted soil was proposed. The implications of the results for seed testing were also highlighted. It was concluded that consideration should be given to the genotype of maize destined for use in ecologies prone to high soil densities. All varieties of maize grown in an agroecological zone could be screened to identify genotypes tolerant of higher soil densities. The seeds could then be multiplied and distributed to farmers.     

Genetic diversity in vegetative traits of utazi (<Emphasis Type="Italic">Gongronema latifolia</Emphasis> Benth) grown for two cropping seasons in Nsukka

Utazi (Gongronema latifolia Benth.) clones obtained from some localities of Southeastern Nigeria were used to establish a research field in a randomized complete block design with three replications. The extent of genetic diversity and selections on the vegetative traits were determined. Results obtained showed diverse genetic base of the clones in the vegetative traits. Higher genetic variability was observed in leaf area/plant, length of the longest vine/plant and number of leaves/plant in the clones. However, significant environmental effect on length of the longest vine/plant and number of vines/plant resulted in lower broad sense heritability estimate value for the traits. The broad sense heritability estimate for size of the cordate base, leaf area, breadth, and length are high ranging from 74–86 %. The year had no significant effect on the traits with high broad sense heritability. Strong positive correlation was observed between length of breadth and leaf area (r = 0.97; n = 46). The principal component analysis indicated that the vegetative traits of the species could be classified based on the leaf area determined by leaf length, breadth and size of the cordate base as well as the quantity of leaves on a clone. The GGE biplot analysis revealed the pattern clones were distinctly positioned; clone EBS-15-NKALAGU had the highest level of all the attributes measured, while EBS-16-ABAKALIKI had the least. Hence, clones EBS-15-NKALAGU, ENS-08-MBU and ENS-12-0KUTU could be selected for improvement and production purposes because they rated high in the vegetative traits with high genetic effects in their expression over the two years.     

Biological Characteristics of Vegetative Growth of Cultivated Saussurea involucrata in a Low Altitude Region

[Objective]To study the biological characteristics of vegetative growth of cultivated Saussurea involucrata in a low altitude region.[Methods]The measure agronomic traits of cultivated S. involucrate were researched,including leaf number,plant height,root length,and fresh weight under different treatments. [Results]The seedling emergence rate could be improved if plots were covered with a straw mat immediately after sowing the seeds. The biomass of spring-sown plants was significantly higher than that of autumn-sown plants. The growth of 1-year-old seedlings was slow from germination to the 45 thday,whereby it increased and reached a moderate rate by 70 d. Characteristics of perennial cultivated plants,such as plant height and leaf number,were stable and changed a little within the current year. Growth of seedlings increased under 60% shade cloth until the stage of 5 true leaves. Cultivated S. involucrata also demonstrated drought tolerance. One-year-old plants could be cut twice in the same year,but 2-and 3-year-old plants four times. Regenerative ability could be promoted by cutting,which was also improved resilience to high temperature and pest damage. [Conclusions] Cultivated S. involucrata in a low altitude region had its own biological characteristics of vegetative growth.     

基于图像处理的冬小麦植被覆盖率测定及其遗传解析

植被覆盖率是反映植株生长势的重要生理性状,在旱作地区尤为重要。图像处理技术能够快速有效地对苗期和孕穗期植被覆盖率进行量化分析。以28份山东小麦主栽品种和品系为材料,在240株 m^-2和360株 m^-2密度下,连续2年测定了孕穗前不同发育阶段的植被覆盖率,并利用921个DArT标记和83个SSR标记分析了与植被覆盖率相关的遗传区段。结果表明。不同密度下,冬小麦植被覆盖率在越冬期、返青期和孕穗期存在显著差异,而起身期基本一致。起身期植被覆盖率与春季最高分蘖数、抽穗后群体叶面积指数、单位面积穗数和籽粒产量均呈显著正相关,r = 0.73~0.76 (P<0.01),表明起身期植被覆盖率可用于预测上述性状。共检测出12个遗传区段与植被覆盖率相关联,大部分区段直接参与调控苗期和孕穗期的生长势。10个遗传区段与已报道的苗期性状、产量性状及抗病位点一致,其中5BL、6AS和6BL染色体上携带的植被覆盖率相关遗传区段与已报道的苗期比叶面积和生物量等位点完全相同。建议将植被覆盖率作为生长势量化指标,用于育种选择和遗传研究。