Determining the growing season of land vegetation on the basis of plant phenology and satellite data in Northern China

The objectives of this study are to explore the relationships between plant phenology and satellite-sensor-derived measures of greenness, and to advance a new procedure for determining the growing season of land vegetation at the regional scale. Three phenological stations were selected as sample sites to represent different climatic zones and vegetation types in northern China. The mixed data set consists of occurrence dates of all observed phenophases for 50–70 kinds of trees and shrubs from 1983 to 1988. Using these data, we calculated the cumulative frequency of phenophases in every 5-day period (pentad) throughout each year, and also drew the cumulative frequency distribution curve for all station-years, in order to reveal the typical seasonal characteristics of these plant communities. The growing season was set as the time interval between 5% and 95% of the phenological cumulative frequency. Average lengths of the growing season varied between 188 days in the northern, to 259 days in the southern part of the research region. The beginning and end dates of the surface growing season were then applied each year as time thresholds, to determine the corresponding 10-day peak greenness values from normalized difference vegetation index curves for 8-km² pixels overlying the phenological stations. Our results show that, at the beginning of the growing season, the largest average greenness value occurs in the southern part, then in the northern, and finally the middle part of the research region. In contrast, at the end of the growing season, the largest average greenness value is measured in the northern part, next in the middle and lastly the southern part of the research region. In future studies, these derived NDVI thresholds can be applied to determine the growing season of similar plant communities at other sites, which lack surface phenological data. Received: 29 November 1999 / Revised: 14 March 2000 / Accepted: 15 March 2000     

猪瘟病毒感染性cDNA克隆的构建及其致病性

为了建立研究猪瘟病毒的技术平台,利用RT-PCR技术构建了猪瘟病毒中国石门株(Shimen)的全长有感染性cDNA克隆pT7SM。通过体外转录线性化的pT7SM并将转录的RNA转染至PK-15细胞中,获得了猪瘟病毒粒子。再用间接免疫荧光法测定了其生长曲线,通过电镜观察到重组病毒呈球形,具有囊膜结构。进一步把获得的猪瘟病毒粒子感染非免疫实验猪,结果子代病毒与石门株类似,对非免疫实验猪有强烈的致病性,证明该全长cDNA克隆可靠稳定,忠实地保留了石门株病毒的感染性和致病特征。由此为进一步探讨猪瘟病毒的致弱机制及病毒与机体相互作用的机制打下了良好的基础。     

非洲猪瘟病毒微滴数字PCR (ddPCR)方法的建立及应用

【目的】非洲猪瘟病毒(African swine fever virus,ASFV)能导致猪群高死亡率,从而造成严重的经济损失。因此,建立严密、高效的防控系统,包括灵敏、准确的诊断方法以及高效的预报预警机制等,以避免ASF传入我国。本文旨在建立一种新型而高灵敏度的ASFV微滴数字PCR(Droplet digital PCR,dd PCR)检测方法。【方法】针对ASFV K205R基因设计一对特异性引物和Taq Man探针,通过反应条件优化,建立了ASFV实时荧光定量PCR(q PCR)和dd PCR检测方法;并对两种方法的线性关系、灵敏性、特异性和重复性进行了评估,利用建立的ASFV检测方法对163份国内和进境的组织样本及血清样本进行检测,血清样本经商品化ASFV ELISA试剂盒复检,评估不同方法检测结果的符合率。【结果】建立的ASFV q PCR和dd PCR检测方法线性关系较好(R2≥0.998),dd PCR的最低检测限度可达到0.36拷贝,在20μL反应体系中约为10拷贝/反应,检测灵敏度是q PCR的10倍。ASFV dd PCR检测方法具有很高的特异性和重复性,不与其他猪常见病毒发生交叉反应。【结论】该方法灵敏度高、特异性强,可作为一种有效的分子生物学方法来诊断ASFV,为防止该病传入我国以及ASFV的实时监测提供新的技术储备,同时促进dd PCR技术在我国的发展和应用。     

Use of bioclimatic indexes to characterize phenological phases of apple varieties in Northern Italy

The research was designed to characterize the phenological behaviour of different apple varieties and to compare different bioclimatic indexes in order to evaluate their adaptability in describing the phenological phases of fruit species. A field study on the requirement for chilling units (winter chilling requirement) and the accumulation of growing degree hours of 15 native apple cultivars was carried out in a fruit-growing area in North West Italy (Cuneo Province, Piedmont). From 1991 to 1993, climatic data were collected at meteorological stations installed in an experimental orchard (Verzuolo, Cuneo). Four methods were compared to determine the winter chilling requirement: Hutchins, Weinberger-Eggert, Utah and North Carolina. The Utah method was applied to determine the time when the chilling units accumulated become effective in meeting the rest requirements. A comparison of the different methods indicated that the Weinberger-Eggert method is the best: as it showed the lowest statistical variability during the 3 years of observations. The growing degree hour requirement (GDH) was estimated by the North Carolina method with two different base temperatures: 4.4°C and 6.1°C. More difficulties were met when the date of rest completion and the beginning of GDH accumulation was determined. The best base temperature for the estimation of GDH is 4.4°C. Phenological and climatic characterizations are two basic tools for giving farmers and agricultural advisors important information about which varieties to choose and which are the best and the most correct cultivation practices to follow. Received: 25 October 2000 / Revised: 6 August 2001 / Accepted: 6 August 2001     

Genotype imputation from various low-density SNP panels and its impact on accuracy of genomic breeding values in pigs

The uptake of genomic selection (GS) by the swine industry is still limited by the costs of genotyping. A feasible alternative to overcome this challenge is to genotype animals using an affordable low-density (LD) single nucleotide polymorphism (SNP) chip panel followed by accurate imputation to a high-density panel. Therefore, the main objective of this study was to screen incremental densities of LD panels in order to systematically identify one that balances the tradeoffs among imputation accuracy, prediction accuracy of genomic estimated breeding values (GEBVs), and genotype density (directly associated with genotyping costs). Genotypes using the Illumina Porcine60K BeadChip were available for 1378 Duroc (DU), 2361 Landrace (LA) and 3192 Yorkshire (YO) pigs. In addition, pseudo-phenotypes (de-regressed estimated breeding values) for five economically important traits were provided for the analysis. The reference population for genotyping imputation consisted of 931 DU, 1631 LA and 2103 YO animals and the remainder individuals were included in the validation population of each breed. A LD panel of 3000 evenly spaced SNPs (LD3K) yielded high imputation accuracy rates: 93.78% (DU), 97.07% (LA) and 97.00% (YO) and high correlations (>0.97) between the predicted GEBVs using the actual 60 K SNP genotypes and the imputed 60 K SNP genotypes for all traits and breeds. The imputation accuracy was influenced by the reference population size as well as the amount of parental genotype information available in the reference population. However, parental genotype information became less important when the LD panel had at least 3000 SNPs. The correlation of the GEBVs directly increased with an increase in imputation accuracy. When genotype information for both parents was available, a panel of 300 SNPs (imputed to 60 K) yielded GEBV predictions highly correlated (⩾0.90) with genomic predictions obtained based on the true 60 K panel, for all traits and breeds. For a small reference population size with no parents on reference population, it is recommended the use of a panel at least as dense as the LD3K and, when there are two parents in the reference population, a panel as small as the LD300 might be a feasible option. These findings are of great importance for the development of LD panels for swine in order to reduce genotyping costs, increase the uptake of GS and, therefore, optimize the profitability of the swine industry.     

Evaluation of an on-farm method to assess colostrum IgG content in sows

The objective of this work was to investigate the evaluation of swine colostrum immunoglobulin G (IgG) concentration using the Brix refractometer. Colostrum samples were collected across all teats, from 124 sows of mixed parities. According to sampling time, three categories were created: samples available from 9 h before the onset of parturition until the first piglet was born were classified as before farrowing; samples collected after the first birth until 4 h later were classified as during farrowing; and finally samples collected from this point until 14 h after parturition, were classified as after farrowing. Samples were drawn and divided into three portions; one was immediately analyzed, a second was refrigerated and the third was frozen at −20°C. Fresh and refrigerated colostrum samples were analyzed at the farm with a Brix refractometer. IgG content of frozen samples was analyzed using a Brix refractometer, with a subset of 42 samples also tested with a commercially available radial immune diffusion (RID) kit. The Brix percentage ranged from 18.3% to 33.2%. Brix percentage repeatability, assessed by the intraclass correlation coefficient (ICC), was very strong (fresh ICC=0.98, refrigerated ICC=0.88 and frozen ICC=0.99). One-way repeated-measures ANOVA showed that storage temperature did not affect BRIX percentage of colostrum IgG (P>0.05). ANOVA results show a significant effect of sampling time on colostrum immunoglobulin concentration, measured with both Brix and RID (Brix: P<0.003; RID: P<0.05). Immunoglobulin G concentration measured by RID ranged from 13.27 to 35.08 mg/ml. Pearson correlation coefficient revealed that Brix percentage was positively correlated (r=0.56, P<0.001) with RID results (regression equation: RID=1.01 (±0.2) Brix −1.94 (±5.66); R²=0.31). The results of this study indicate that the Brix refractometer provides a simple, fast and inexpensive estimation of colostrum IgG in sows.     

Nutrient dynamics of reindeer forage species along snowmelt gradients at different ecological scales

Growing season nutrient dynamics of four reindeer forage species (Betula nana, Eriophorum angustifolium, Rumex acetosa and Vaccinium myrtillus) were studied in a mountainous sub-arctic landscape in N Sweden. Changes in nitrogen (N), phosphorus (P) and fibre (ADF) concentrations in leaves and shoots were analysed (from a reindeer foraging perspective) along four ecological gradients significant to regional and local snowmelt regimes: season, oceanicity, altitude, and snow-patch retreat. N and P concentrations showed marked seasonal variations with peaks occurring from the middle of June to the end of July depending on species and snowmelt progression. The seasonal pattern for ADF concentrations, as well as differences between snowmelt regimes, were less consistent and showed large differences between species. N concentrations increased along snowmelt gradients at small (within snow-patches) and medium (along altitude gradients) spatial scales. Furthermore, variations in N concentrations were temporally and spatially scale-dependent, which underlines the importance of scale for understanding plant nutrient dynamics in sub-arctic and alpine systems, as well for plant–animal interactions. The greatest temporal and spatial differences in nutrient quality were observed early in the season, i.e., at the time of highest nutrient requirements for reindeer. Climate-induced changes of the start and the progress of the growing season may result in significant consequences to the development of calves and subsequently to the population demography of reindeer, mediated through spatial and temporal changes in the distribution of high quality food. These results provide basic knowledge for reindeer management in the light of the ongoing global warming.     

Effect of irradiance and plant age on the dimensions of the growing shoot of poplar

Populus euramericana (Dode) Guinier cv. Robusta plants were cultivated at irradiances of 7.5, 15 and 30 W m⁻² (32.5, 65 and 130 μmol m² s⁻¹), 400–700 nm at 22°C and a relative humidity between 40 and 60% on a gravel culture subirrigated with Hoagland's nutrient solution. The basal diameter of the growing shoot, a measure of the number of apical cells participating in growth, increased proportionally to irradiance and was correlated with mature leaf length. The development of the length of the growing shoot (L_gs) depended also on the nutritional status of the (young) shoot. L_gs was strongly correlated with the rate of height growth.     

中国西藏部分地区猪戊型肝炎病毒流行病学调查

戊型肝炎病毒(Hepatitis E Virus,HEV)感染是一个重要的全球公共卫生问题,而猪被认为是HEV的天然宿主。HEV可以跨种间传播,且已经证实生吃感染的猪肉会导致人感染。在中国西藏许多地区仍然有生吃猪肉、猪肝等的习惯,且不同种家畜混合饲养,极易造成HEV感染和传播。然而中国西藏地区猪HEV流行情况报道甚少。文中对中国西藏5个地区市(拉萨、日喀则、山南、那曲和昌都)猪血清进行HEV Immunoglobulin-M(Ig M)和Ig G抗体检测,并通过逆转录巢氏PCR(RT-n PCR)进行HEV RNA检测和定量RT-PCR(q RT-PCR)进行病毒拷贝计算,首次报道了藏猪血清HEV RNA阳性率。结果显示,在西藏猪中HEV有较高的流行趋势。猪血清HEV Ig M抗体阳性率高达7.6%(26/340),HEV Ig G抗体阳性率为1.8%(6/340),HEV RNA阳性率高达7.6%(26/340),血清中病毒拷贝高达1.7×107 copies/m L,而且5个地区有不同的流行趋势。结果表明西藏猪HEV感染情况严重。有关部门应加强管理,以避免人与动物之间的交叉感染和暴发。