An assessment of the reference watershed approach for TMDLs with biological impairments     

Rachel C. Wagner  Theo A. Dillaha  Gene Yagow 《Water, air, and soil pollution》2007,181(1-4):341-354

The Reference Watershed Approach (RWA) is used in TMDL development for biological and other impairments with narrative water quality criteria. The questions addressed in this research include: (1) With the RWA, how do land use classifications from different data sources (Digital Ortho-Quarter Quads (DOQQ) and National Land Cover Dataset (NLCD)) impact simulated pollutant loadings? (2) With the RWA, what is the impact of alternative water quality models (GWLF and SWAT) on pollutant loadings? (3) With the RWA, how sensitive are simulated pollutant loadings to the use of different reference watersheds? Various combinations of land use, water quality model, and reference watershed resulted in pollutant reductions that ranged from ?13 to 88%. In a comparison of the use of NLCD versus DOQQ-based land use data with the GWLF model, differences in required reductions ranged from 13 to 74% for three different reference watersheds. Use of alternative water quality models with DOQQ land use data resulted in differences in required sediment reductions from ?43 to 8% for the three reference watersheds. Differences in load reduction requirements were also seen when different reference watersheds were used, regardless of the water quality model or the land use source used. With DOQQ land use, required sediment reductions ranged from 18 to 88% and 37 to 82%, for the SWAT and GWLF models, respectively. These results suggest that explicit margins of safety used to account for modeling uncertainties during TMDL development may need to be substantially greater than 20% when using the reference watershed approach.  相似文献   

Genetic diversity in cucumber (Cucumis sativus L.): I. A reevaluation of the U.S. germplasm collection     

Vladimir Meglic  Felix Serquen  Jack E. Staub 《Genetic Resources and Crop Evolution》1996,43(6):533-546

Genetic variation within the U.S. cucumber collection (Cucumis sativus var. sativus L. and var. hardwickii (Royle) Alef.) was assessed by examing the variation at 21 polymorphic isozyme loci and comparing the results of this investigation with a similar previous analysis of 14 loci. About 29% (15 of 51) of the enzyme systems examined in an initial survey were polymorphic. Seven loci (Ak-2, Ak-3, Fdp-1, Fdp-2, Mpi-1, Pep-gl and Skdh) which were not previously used to estimate genetic diversity, were assessed. On average, 1.4 loci were polymorphic per enzyme system and 2.2 alleles were present per polymorphic locus. The frequency of polymorphisms was relatively low for Fdp-1(2) (0.01), Mpi-1(1) (0.03), and Skdh(1) (0.02). Principal component and cluster analyses of allelic variation at polymorphic loci separated a diverse array of 757 cucumber accessions from the U.S. National Plant Germplasm Systesm's (NPGS) collection into distinct groups by country (45 nations examined). All accessions of C. s. var. sativus were isozymically distinct from C. s. var. hardwickii, which were themselves dissimilar from each other. Data suggest that C. s. var. hardwickii is not a feral derivative of extant C. s. var. sativus populations. The allelic profile of C. s. var. sativus accessions originating from Burma, Thailand, Indonesia, Hong Kong, Zimbabwe and Ethiopia were distinct from the other accessions examined. Allelic fixation has occurred at Pgd-2 in accessions from Burma, and at Ak-2 in accessions from Zimbabwe and Ethiopia. Some of the countries examined that were in close geographic proximity (e.g., Thailand, Indonesia and Hong Kong) contained accessions with similar isozyme profiles. Accessions are fixed for certain alleles [e.g., Gr(1) (100%), Fdp-1(1) (100%) and Mpi-2(2) (50%) for accessions from Thailand, Indonesia and Hong Kong]. Grouping countries by continent or sub-continent (i.e., North and South American, China, Eastern Europe, Western Europe) and by numbers of accessions examined (i.e., India/Burma, Iran, Japan, Turkey, and remaining accessions) was used to identify accessions with unique allozymic profiles [PIs 209064 (USA), 257486 (China), 188749 (Egypt), 285607 (Poland), 369717 (Yugoslavia), 357844 (Poland), 255936 (Netherlands), 183127 (India), 200818 (Burma), 200815 (Burma), 137836 (Iran), 227013 (Iran), 227235 (Iran), 451976 (Japan), 181752 (Syria), 181874 (Syria), 169383 (Turkey), 171613 (Turkey)].  相似文献   

Spanish melons (Cucumis melo L.) of the Madrid provenance: a unique germplasm reservoir     

Sandra Escribano  Almudena Lázaro  Hugo E. Cuevas  Ana I. López-Sesé  Jack E. Staub 《Genetic Resources and Crop Evolution》2012,59(3):359-373

Melon (Cucumis melo L.) landraces of the Madrid provenance, Spain, have received national distinction for their high fruit quality and sensorial attributes. More specifically, a unique array of Group Inodorus landraces have been continuously cultivated and conserved by farmers in the municipality of Villaconejos since the 19th century. Their genetic relationships to other Group Inodorus and Flexuous melon market classes is not known, and, thus, a study was designed to determine their genetic relationships using 52 simple sequence repeat (SSR) markers, and then make genetic comparisons between these accessions and a previously published “Standard Reference Germplasm Array” (RA) containing Group Inodorus (14 Spanish and one USA), Flexuosus (1 Spanish), and Cantalupensis ( 2 USA) melon accessions. This subset consisted of 15 Spanish Group Inodorus landraces that circumscribed the genetic variation of major Spanish melon market classes (Groups Inodorus and Flexuosus), and USA commercial varieties (Groups Cantalupensis and Inodorus). Based on genetic distances, Villaconejos (Madrid) genotypes differed substantially from RA subset accessions, thus defining their genetic uniqueness. Principal component analysis (PCA) partitioned the accessions examined into four distinct groups revealing that Villaconejos black epidermis melons (landraces ‘Largo’, ‘Largo Negro Escrito’ and ‘Puchero’) were distinctly different from all other accessions examined, as cluster analysis separated Rochet market type Villaconejos’ accessions (landraces ‘Mochuelo’, ‘Mochuelo Tradicional’ and ‘Melón de Villaconejos’) from RA of the same market type. Genetic assessment of principal Spanish market classes revealed comparatively low intra-market heterogeneity in Piel de Sapo type accessions and high heterogeneity in Black and Yellow market type accessions. While a relatively high level of genetic introgression was detected between Yellow and Green market types, black epidermis market types were genetically unique. Given the uniqueness and high genetic diversity resident in Villaconejos landraces, this germplasm pool should be considered as a genetic source for broadening the comparatively narrow genetic base of Group Cantalupensis and Inodorus melon market types, especially standard commercial Spanish Group Inodorus market types (e.g., Piel de Sapo, Rochet, and Canari).  相似文献   

Spatial distribution of spiders and epedaphic Collembola in an environmentally heterogeneous forest floor habitat     

Elvira Sereda  Theo Blick  Wolfgang H.O. Dorow  Volkmar Wolters  Klaus Birkhofer 《Pedobiologia》2012,55(5):241-245

Describing the biotic and abiotic processes that are responsible for the formation of spatial patterns in predators and their prey is crucial for improving our understanding of food–web interactions. We studied the spatial distribution of four abundant spider species and three common groups of epedaphic Collembola prey in a beech-dominated (Fagus sylvatica) forest floor habitat and related the observed patterns to environmental heterogeneity, overall predator activity (all ground beetles and spiders) and prey availability (all Collembola) at the local scale. Spiders and epedaphic Collembola were sampled over 392 days in a spatially explicit design based on a regular grid of 25 pitfall traps (inter-trap distance 100 m). Environmental heterogeneity was characterized by cover of moss and litter as well as the amount of dead wood at each trap location. We first used the index of dispersion to characterize the spatial distribution of spider species and Collembola and then related the observed patterns to environmental heterogeneity, predator and prey availability while testing for spatial autocorrelation within the same models. All taxa were significantly more aggregated than expected from the assumption of random distribution. The distribution of spider species was positively (Coelotes terrestris) or negatively (Tenuiphantes zimmermanni and Tapinocyba insecta) related to the cover of moss and negatively related to litter cover (C. terrestris) or the local availability of prey (T. insecta). The distribution of Collembola was negatively related to local litter cover (Lepidocyrtus spp.) and positively related to the amount of medium deadwood pieces (all other Entomobryidae). Our study suggests that none of the spider species preferred areas of low overall predator activity density. Moreover, it does not indicate association of spider species to prey-rich areas at the analyzed scale of 100 m. It further highlights the importance of environmental heterogeneity, as different habitat properties differentially affected the local activity density of spiders and Collembola and thus considerably contributed to the understanding of distribution patterns.  相似文献   

Effects of root fragmentation on generative reproduction of Sonchus arvensis     

Saghi Anbari  Anneli Lundkvist  Johannes Forkman  Theo Verwijst 《Acta Agriculturae Scandinavica, Section B - Plant Soil Science》2016,66(5):391-398

To develop better mechanical management strategies, more information on the impact of root partitioning on generative reproduction of Sonchus arvensis L. is needed. Therefore, an outdoor experiment was performed in Sweden in 2008, to evaluate the effect of root fragmentation on generative reproduction of S. arvensis. Two artificial populations of S. arvensis with the same total root length per area but with different initial root lengths and different numbers of root fragments were planted. Cumulative numbers of flower receptacles which had shed mature seeds over the season were assessed. Changes in the number of seeds per flower receptacle and average seed weight were monitored over time during the late season. Plants from long root fragments produced more flower receptacles than plants from short ones. Per area, however, the number of mature flower receptacles did not differ. The number of seeds per flower receptacle and individual seed weight were not affected by initial root length for the first cohort of shoots which sprouted from the initially planted roots. A second cohort, from roots produced during the season, resulted, irrespective of its initial root length, in fewer flower receptacles per plant and per area, with less seeds per receptacle, but with the same average seed weight as the first cohort. The number of seeds per flower receptacle was higher in mid-September than earlier or later. Average seed weight slightly decreased over time. The weight of seeds produced in early September was inversely related to the number of seeds per receptacle, but this trade-off disappeared over time. Root fragmentation alone in pure populations of S. arvensis does not impede generative reproduction, but is likely to decrease input of seeds to the seed bank, when combined with crop competition.  相似文献   

Backcross introgression of plastomic factors controlling chilling tolerance into elite cucumber (Cucumis sativus L.) germplasm: early generation recovery of recurrent parent phenotype     

Vanessa S. Gordon  Jack E. Staub 《Euphytica》2014,195(2):217-234

Environmental stresses such as chilling temperatures can decrease germination, emergence, flower and fruit development, marketable yield, and postharvest fruit storage longevity in cucumber (Cucumis sativus L.). While response to chilling injury in cucumber is controlled by simple plastidic (maternal) and nuclear (paternal) factors, no chilling tolerant U.S. processing varieties are commercially available. Furthermore, even though three single nucleotide polymorphic sites have been identified as plastid components associated with chilling tolerance in cucumber, it is not known how these factors interact with nuclear factors controlling economically important traits. Therefore, an experiment was designed to evaluate the rate of recovery of the chilling susceptible (cytoplasm) genotype during introgression backcrossing (IB), where it was used as a recurrent parent after the initial mating to a line possessing chilling tolerant cytoplasm (donor parent). Phenotypic yield and quality trait data were collected on processing type backcross progeny (BC_1–5 and BC₂S₃) derived from an initial ‘Chipper’ (tolerant) × line M 29 (susceptible) mating, and rate of progression to the recurrent parent was determined by simple sequence repeat marker and morphological trait analyses. Substantial degrees of the recurrent parent phenotype and nuclear genome were recovered by the BC₂ generation (P = 0.001), with nearly complete recovery of recurrent parental traits and its nuclear genome occurring by the BC₃. General combining ability (GCA) of derived BC₂S₃ lines was significant for yield, yield/plant, length (L), diameter (D), and L:D ratios. The BC₂S₃ line GCA and rate of progression towards the recurrent parent for economically important traits suggests that elite chilling tolerant cucumber germplasm can be developed rapidly through IB and marker genotyping.  相似文献   

Macroscopic hierarchical surface patterning of porphyrin trimers via self-assembly and dewetting     

van Hameren R  Schön P  van Buul AM  Hoogboom J  Lazarenko SV  Gerritsen JW  Engelkamp H  Christianen PC  Heus HA  Maan JC  Rasing T  Speller S  Rowan AE  Elemans JA  Nolte RJ 《Science (New York, N.Y.)》2006,314(5804):1433-1436

The use of bottom-up approaches to construct patterned surfaces for technological applications is appealing, but to date is applicable to only relatively small areas (approximately 10 square micrometers). We constructed highly periodic patterns at macroscopic length scales, in the range of square millimeters, by combining self-assembly of disk-like porphyrin dyes with physical dewetting phenomena. The patterns consisted of equidistant 5-nanometer-wide lines spaced 0.5 to 1 micrometers apart, forming single porphyrin stacks containing millions of molecules, and were formed spontaneously upon drop-casting a solution of the molecules onto a mica surface. On glass, thicker lines are formed, which can be used to align liquid crystals in large domains of square millimeter size.  相似文献   

小麦赤霉菌绿色荧光蛋白标记突变体的侵染研究     

张旭  Theo  van  de  Lee  陆维忠  喻大昭  马鸿翔 《中国农业科学》2008,41(10):3077-3082

 【目的】赤霉病是危害大麦、小麦生产的世界性病害,研究病原菌的致病过程对于病害的控制有重要意义。【方法】本研究利用绿色荧光蛋白（GFP）标记的禾谷镰刀菌回复突变体以单花滴注方法进行人工接种研究不同突变体的致病力差异及其在小麦穗部的侵染过程。【结果】269株回复突变体的致病力存在明显分化。接种6 d后,致病力明显降低的突变体,只有接种小穗发病,致病力明显增强的突变体,病症可扩展至5个小穗。GFP荧光信号检测表明,弱致病突变体在接种后仅在接种小穗内生长、延伸,并终止于小穗基部的致密组织处。而强致病力突变体在接种小穗内生长2 d后,即能够通过小穗基部的致密组织到达小麦穗轴,并沿着穗轴内部微管束组织和皮层组织向上和下延伸,侵入邻近小穗。【结论】病原菌在接种小穗中生长后,沿着柱头、子房或内、外稃内表面,经过靠近穗轴的致密组织,侵入邻近小穗,感染整个麦穗,直至到达茎秆。  相似文献   

Prevalence,prediction and risk factors of enteropathogens in normal and non-normal faeces of young Dutch dairy calves     

Chris J.M. Bartels  Menno Holzhauer  Ruurd Jorritsma  Wim A.J.M. Swart  Theo J.G.M. Lam 《Preventive veterinary medicine》2010,93(2-3):162-169

Between January and April 2007, 424 calves under 22 days of age from 108 Dutch dairy herds were sampled to estimate the prevalence of non-normal faeces (‘custard-like’—yellowish-coloured with custard consistency or diarrhoea: watery-like faeces) and the shedding of enteropathogens Escherichia coli K99 (E. coli), Coronavirus, Cryptosporidium parvum (C. parvum), Rotavirus and Clostridium perfringens (Cl. perfringens). In addition, information was collected on animal characteristics and herd-management practices. The probability of detecting each one of five enteropathogens given a calf with ‘custard-like’ faeces or diarrhoea was estimated using Bayes’ rule and was based on the predicted probabilities from a multinominal model including each of five enteropathogens as independent variables. In addition, putative risk factors for the presence of each of five enteropathogens were analysed using logistic regression models with random herd effects.Fifty-seven percent of calves had faeces of normal colour (brownish) and consistency (firm), 23.8% (95%CI: 19.8–28.2%) had ‘custard-like’ faeces and 19.1% (95%CI: 15.5–23.2%) had diarrhoea. E. coli was the least detected enteropathogen (2.6% (95%CI: 1.3–4.6%) of calves, 9% (95%CI: 5–16%) of herds) and Cl. perfringens was most detected (54.0% (95%CI: 49.1–58.8%) of calves, 85% (95%CI: 77–91%) of herds). E. coli and Coronavirus were detected incidentally in only one or two calves per herd, whereas C. parvum and Cl. perfringens were frequently detected in up to four calves per herd. For calves with ‘custard-like’ faeces, the probability of detecting Rotavirus from a calf in its first week of age was 0.31 whereas for a calf in its second week, there was a 0.66 probability of detecting C. parvum. The probabilities of detecting E. coli, Rotavirus and C. parvum in calves with diarrhoea in their first week of age were 0.10, 0.20 and 0.43, respectively. In calves with diarrhoea between 1 and 2 weeks of age, the probability of detecting enteropathogens was 0.43 for C. parvum. None of the tested enteropathogens were related to ‘custard-like’ faeces or diarrhoea in the third week of age.Putative risk factors for E. coli, Coronavirus and C. parvum included the presence of peer-calves shedding Coronavirus, C. parvum or Rotavirus, respectively. Additionally, managerial risk factors such as non-optimal hygienic housing (for Coronavirus) and the routine use of antibiotics for diarrhoeic calves (for C. parvum) were found. No animal or managerial factors were associated with shedding of Cl. perfringens.  相似文献   

Foreword     

Theo Schetters  Monica Florin-Christensen 《Veterinary parasitology》2010,167(2-4):91

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