Tuber growth and biomass partitioning of two potato cultivars grown under different n fertilization rates with and without irrigation

Nitrogen and water deficiencies are known to affect potato yield, but much less is known of their effect on tuber growth and biomass partitioning. The objective of this on-farm study conducted at two sites in each of three years, 1995 to 1997, was to determine the effects of supplemental irrigation and N fertilization rates on tuber growth and biomass partitioning of the cultivars Shepody and Russet Burbank. The N fertilization rates were 0,100, and 250 kg N ha^-1in 1995, and 0, 50,100, and 250 kg N ha_?1 in 1996 and 1997. The highest bulking rate observed in our study (7.3 g fresh tubers m^-2 °C^-1) can be considered near the potential bulking rate in New Brunswick. The water deficit in the absence of supplemental irrigation reduced this potential bulking rate by as much as 40%, but this reduction was much less at five of six sites and negligible at two of six sites. Nitrogen deficiency reduced the bulking rate at two of six sites. This negative effect of N deficiency on bulking rate was greater with irrigation than without irrigation at two of six sites; the tuber bulking rate with irrigation was reduced by as much as 50% with no N applied at one site. Shepody had a greater bulking rate than Russet Burbank. The tuber bulking of Russet Burbank, however, started earlier and lasted longer than that of Shepody. Water and N deficiencies increased biomass partitioning to tubers and large roots. Shepody partitioned a greater proportion of its biomass to large roots and had a greater root biomass than Russet Burbank. Our results demonstrate the ability of potatoes to modify biomass partitioning when grown under water and/or N stresses. As a result of this compensation, the reduction in tuber yield due to limited N and water stresses is minimized.     

Critical Nitrogen Curve and Nitrogen Nutrition Index for Potato in Eastern Canada

Plant diagnostic methods of N deficiency should be based on the definition of a critical N concentration, that is the minimal N concentration required to achieve maximum growth. The critical N concentration (N_c) of potato was determined from six on-farm field trials in which two cultivars (Russet Burbank and Shepody) were grown under three or four N rates with and without irrigation. Dry matter yield and N concentration of shoots and tubers were determined approximately weekly during the growing season. The N_c was determined by selecting data points for which the highest total biomass comprised of shoots and tubers was obtained, and by expressing N concentration (N) as a function of total biomass (W). The N nutrition index (NNI), calculated as the ratio between measured N concentration and predicted N_c during the growing season, was then related to the relative yield measured at harvest. Under non-limiting water conditions, the allometric relationship between N_c and total biomass for Russet Burbank (N_c = 4.57W^-0.42) was different from that of Shepody (N_c = 5.04W^-0.42), indicating that Shepody had a greater N concentration than Russet Burbank. The N concentration of Shepody was also greater than that of Russet Burbank under limiting water conditions. These results suggest that there is intra-specific variability in potato for the relationship between N concentration and biomass. The NNI ranged from 0.50 to 1.4. The relationship between relative yield and NNI expressed by a quadratic function accounted for a greater proportion of the variability with irrigation (71% for Russet Burbank and 82% for Shepody) than without irrigation (65% for Russet Burbank and 32% for Shepody). Our results suggest that the NNI could be a reliable indicator of the level of N stress during the growing season, particularly under non-deficient water conditions.     

Immersive landscapes: modelling ecosystem reference conditions in virtual reality

Landscape Ecology - Understanding the variability and dynamics of ecosystems, as well as their responses to climate or land use change, is challenging for policy makers and natural resource...     

Genetic structure and gene flow in Beta vulgaris subspecies maritima along the Atlantic coast of France

Locating and quantifying genetic variation within crop wild relatives is an ongoing activity of gene banks tasked with ex situ conservation. Without detailed information about the population genetics of a species, geography often serves as a reasonable proxy for differentiation. With this in mind, this paper examines the genetic diversity and differentiation of Beta vulgaris subsp. maritima accessions collected along a well-studied latitudinal gradient along the French Atlantic coast of France as well as Corsica, for use as representative genotypes from the Mediterranean basin. The aim of this work is to identify the scale and magnitude of differentiation and diversity in this set of accessions, using both molecular and quantitative traits. We assessed clinal variation and admixture in genetic and morphometric data along this latitudinal gradient. Results from this study revealed a complex pattern of recent gene flow and immigration on a historical biogeographic structure. Our data suggest that a presumed latitudinal cline is in reality an admixed mosaic of genotypes.     

Shrub-interspace dynamics alter relationships between microbial community composition and belowground ecosystem characteristics

In desert ecosystems, belowground characteristics are influenced chiefly by the formation and persistence of “shrub-islands of fertility” in contrast to barren plant interspaces. If soil microbial communities are exclusively compared between these two biogeochemically distinct soil types, the impact of characteristics altered by shrub species, especially soil C and N, are likely to be overemphasized and overshadow the role of other characteristics in structuring microbial composition. To determine how belowground characteristics influence microbial community composition, and if the relative importance of these characteristics shifts across the landscape (i.e., between and within shrub and interspace soils), changes in microbial communities across a 3000-year cold desert chronosequence were related to 27 belowground characteristics in surface and subsurface soils. When shrub and interspace communities in surface and subsurface soils were combined across the entire chronosequence, communities differed and were primarily influenced by soil C, NO₃⁻ concentrations, bulk density, pH, and root presence. Within shrub soils, microbial communities were shrub species-specific, especially in surface soils, highlighting differences in soil characteristics created by specific shrub species and/or similarity in stresses structuring shrub species and microbial communities alike. Microbial communities in shrub soils were not influenced by soil C, but by NO₃⁻ and NH₄⁺ concentrations, pH, and silt in surface soils; and Cl, P, soil N, and NO₃⁻ concentrations in subsurface soils. Interspace soil communities were distinct across the chronosequence at both depths and were strongly influenced by dune development. Interspace communities were primarily associated with soil stresses (i.e., high B and Cl concentrations), which decreased with dune development. The distribution of Gram-positive bacteria, Actinobacteria, and fungi highlighted community differences between and within shrub and interspace soils, while Gram-negative bacteria were common in all soils across the chronosequence. Of the 27 belowground characteristics investigated, 13 separated shrub from interspace communities, and of those, only five emerged as factors influencing community composition within shrub and interspace soils. As dunes develop across this cold desert chronosequence, microbial community composition was not regulated primarily by soil C, but by N and P availability and soil stresses in shrub soils, and exclusively by soil stresses in interspace soils.     

Development and evaluation of a noninvasive marker cluster technique to assess three-dimensional kinematics of the distal portion of the forelimb in horses

OBJECTIVE: To develop and evaluate a marker cluster set for measuring sagittal and extrasagittal movement of joints in the distal portion of the forelimb in ponies. ANIMALS: 4 ponies. PROCEDURES: 5 infrared cameras were positioned on a concrete walkway in a frontal-sagittal arc and calibrated. Four segments were defined: hoof, middle phalanx, proximal phalanx, and metacarpus. Rigid clusters with 4 retroreflective markers were placed on each segment. A static trial was recorded with additional anatomic markers on the medial and lateral joint lines. Those anatomic markers were removed, and kinematic data were recorded at 240 Hz during walking. An ensemble mean was computed from the 4 ponies from 5 replicates of the walks. Joint kinematic variables were calculated by use of the calibrated anatomical system technique. The design and error dispersion of each marker were evaluated. RESULTS: Marker clusters were quasiplanar, but variation in orientation error was reduced because the mean radii were > 10 times the largest error dispersion values. Measurements of sagittal rotations of the distal interphalangeal, proximal interphalangeal, and metacarpophalangeal joints were similar to measurements obtained with bone-fixed triads, but larger discrepancies between the 2 methods were found for extrasagittal rotations. CONCLUSIONS AND CLINICAL RELEVANCE: Development of noninvasive methods for quantifying data pertaining to 3-dimensional motion in horses is important for advancement of clinical analysis. The technique used in the study enabled identification of flexion-extension motions with an acceptable degree of accuracy. Appropriate correction algorithms and improvements to the technique may enable future quantification of extrasagittal motions.     

Partitioning and inhibition of lipid oxidation in mechanically separated turkey by components of cranberry press cake

Extracts from cranberry press cakes were prepared either using ethanol or an ethyl acetate-acetone mixture. The press cake extracts were compared with extracts from cranberry juice powder (CJP), prepared using chloroform:methanol (1:1), for their ability to inhibit lipid oxidation in mechanically separated turkey (MST). Because of the susceptibility of muscle membrane lipids to oxidation, the ability of quercetin in the extracts to partition between the aqueous and the membrane phases was studied. Membrane suspensions were prepared from MST. Partitioning of quercetin was quantified using high-performance liquid chromatography. Oxidation was studied by measuring thiobarbituric acid reactive substances and lipid peroxides. The effectiveness of the extracts to inhibit lipid oxidation was CJP extract > ethyl acetate extract of press cake > or = ethanol extract of press cake. The amount of quercetin in the extracts and the amount of quercetin that partitioned into the membranes followed the same order. However, the total phenolic content of the extracts did not follow the same order as that of inhibitory power. The phenolic content of the extracts decreased, ethyl acetate extract > ethanol extract of press cake > or = chloroform extract of CJP. Irrespective of the extraction method, around 78% quercetin from the extracts partitioned into the membranes. It could be concluded that increasing the amount of quercetin in the press cake extracts increases the ability of the extracts to inhibit lipid oxidation in MST. Hence, a proper choice of solvents and extraction method, which would increase the amount of quercetin in the press cake extracts, might increase the antioxidant potential of the extracts and hence their economic value.     

Assessing genetic diversity of wild southeastern North American <Emphasis Type="Italic">Vaccinium</Emphasis> species using microsatellite markers

Wild species representatives from Northwestern, Central and Southern Florida, and neighboring U.S. states were collected in multiple United States Department of Agriculture (USDA) exploration expeditions and are being preserved at the USDA, Agricultural Research Service, National Clonal Germplasm Repository in Corvallis, Oregon. Germplasm from these southeastern regions of North America is particularly vulnerable to loss in the wild due to encroachment of human development in key habitats and biotic and abiotic stresses from climate change. Fourteen simple sequence repeats (SSRs), previously developed from the highbush blueberry (Vaccinium corymbosum) cultivar ‘Bluecrop’, were used to estimate genetic diversity and genetic differentiation of 67 diploid individuals from three species, including 19 V. elliottii, 12 V. fuscatum, and 35 V. darrowii accessions collected throughout the species’ ranges. Results from our analyses indicated that the samples from each species could be reliably resolved using genetic distance measures with ordination and neighbor joining approaches. In addition, we estimated admixture among these species by using Bayesian assignment tests, and were able to identify a mis-labeled accession of V. darrowii ‘Johnblue’, two mis-classified accessions (CVAC 735.001 and CVAC 1223.001), and four accessions of previously undescribed hybrid origin (CVAC 734.001, CVAC 1721.001, CVAC 1741.001, and Florida 4B CVAC 1790). Allele composition at the 14 SSRs confirmed that Florida 4B CVAC 1790, the donor of low chilling for the southern highbush blueberry, was the critical parent of US 74. Genetic diversity assessment and identification of these wild accessions are crucial for optimal germplasm management and expand opportunities to utilize natural variation in breeding programs.     

The efficacy of triclabendazole and other anthelmintics against Fasciola hepatica in controlled studies in cattle

In eight controlled tests 274 cattle were used to assess the efficacies of triclabendazole, albendazole, clorsulon, nitroxynil, oxyclozanide and rafoxanide against Fasciola hepatica. Against one-, two- and four-week-old early immature fluke the mean efficacies of triclabendazole given orally at 12 mg/kg were 88.1, 95.3 and 90.7 per cent, respectively. Clorsulon, nitroxynil and rafoxanide administered at recommended dose rates showed negligible activity against these stages of the parasite. Against six- and eight-week-old infections the mean efficacies of triclabendazole at 12 mg/kg were 87.5 per cent and 95.7 per cent, respectively. Against F hepatica aged six weeks, albendazole and oxyclozanide showed no activity and clorsulon, nitroxynil and rafoxanide had only slight to moderate activity. The efficacies of triclabendazole, clorsulon, nitroxynil and rafoxanide against 10- or 12-week-old parasites were 100, 99.0, 99.1 and 90.1 per cent, respectively. Albendazole and oxyclozanide showed poor efficacy against 12-week-old infections.