A geographical approach to identify phosphorus-efficient genotypes among landraces and wild ancestors of common bean

Cultivars of common bean (Phaseolus vulgaris L.) capable of yielding well at low levels of native or added phosphorus (P) are highly desirable in many tropical production systems. The objective of the present study was to identify geographical regions which might be sources of such genotypes. A total of 364 landraces, cultivars and wild genotypes, drawn from a broad geographic range, were divided on the basis of growth habit into four field trials, each comprising two levels of P, stressed and unstressed, on an infertile Andosol in Popayan, Colombia. The regression relationship between grain yield per plant in the presence and in the absence of stress was determined, and each genotype's deviation from this relationship was used as a measure of P-efficiency. There was highly significant variation in efficiency among genotypes in all growth habits, and in climbing beans there were consistent regional differences, superior genotypes being identified with greater frequency among those from Bolivia, West Mexico and South Mexico-West Guatemala. The latter region was promising for prostrate bush genotypes also. Wild beans in general performed relatively poorly; it appears that P-efficiency traits in P. vulgaris have been acquired during or after domestication. These results confirm that genetic differences in P-efficiency exist among common bean genotypes and suggest that these are related to geographic origin. Furthermore, the use of a representative sample of germplasm can help to identify segments of the gene bank that are especially promising as sources of desirable traits. This revised version was published online in July 2006 with corrections to the Cover Date.     

Effects of xylanase treatments on gelling and water-uptaking properties of psyllium

The effects of a commercial food-grade xylanase on the physicochemical properties of psyllium were evaluated. The enzymatic reactions were conducted in solid state at ambient temperature. The enzyme-treated psyllium preparations were analyzed and compared with the starting psyllium for their water-uptake properties, gelling capacities, soluble and insoluble fiber contents, and surface structures. The solid-state xylanase treatment significantly reduced both water-uptake and gelling capacities of psyllium (p < 0.01), with a slight decrease of soluble fiber content, whereas no effect on insoluble fiber content was observed. The xylanase treatment also resulted in a smoother surface structure of psyllium particles. In addition, no special equipment and operation were required to conduct the enzymatic reaction, which generated no waste. These data indicated a potential to improve the physicochemical properties of psyllium by use of the solid-state xylanase reactions to promote the utilization of psyllium fiber in functional foods for promoting human health.     

Influence of a riparian wetland on nitrate and herbicides exported from an agricultural field

Agrochemicals are a major source of nonpoint pollution. Forested corridors along stream channels (riparian zones) are thought to be potential sites for removal of agricultural contaminants from ground and surface waters. First-order riparian wetlands are reputed to be especially effective at groundwater remediation. The study site is a fairly typical (for eastern Maryland) small, first-order stream in an agricultural watershed. Preferential flow supplies most of the stream water within the riparian headwater wetland. This upstream area also contains the highest average stream N and pesticide loads in the entire first-order riparian system. Zones of active groundwater emergence onto the surface display high concentrations of nitrate throughout the soil profile and in the exfiltrating water, whereas inactive areas (where there is no visible upwelling) show rapid attenuation of nitrate with decreasing depths. Atrazine degradation products appear to penetrate more readily through the most active upwelling zones, and there is a correlation between zones of high nitrate and high atrazine metabolite levels. Deethylatrazine/atrazine ratios (DAR) seem to indicate that stream flow is dominated by ground water and that much of the ground water may have reached the stream via preferential flow. Remediative processes appear to be very complex, heterogeneous, and variable in these systems, so additional research is needed before effective formulation and application of riparian zone initiatives and guidelines can be accomplished.     

Antioxidant properties of bran extracts from "Akron" wheat grown at different locations

Bran extracts of Akron wheat grown at four nonirrigated and one irrigated testing locations were examined and compared for their free radical scavenging properties against the 2,2-diphenyl-1-picrylhydrazyl radical (DPPH(*)) and the radical cation ABTS(*)(+), chelating capacities, and total phenolic content (TPC) to determine the potential effects of environmental factors on the antioxidant properties of hard winter wheat. The environmental factors included total solar radiation, average daily solar radiation, and number of hours exceeding 32 degrees C. The results showed that bran samples from different growing locations may significantly differ in their radical scavenging activities against both DPPH(*) and ABTS(*)(+), chelating capacities, and TPC. A significant negative correlation was detected between the chelating activities of the bran samples from the four nonirrigated locations and total solar or daily average solar radiation (r = -0.999 and P = 0.001). These data suggest potential influences of growing conditions on the antioxidant properties of hard winter wheat and the possibility of producing wheat that is strong in a selected antioxidant property by optimizing the growing conditions of a selected wheat variety. More research is required to further investigate the relationship among antioxidant properties and environmental factors using different wheat varieties and larger sample sizes.     

Modelling the population dynamics of the Mt. Graham red squirrel: Can we predict its future in a changing environment with multiple threats?

The Mt. Graham red squirrel (Tamiasciurus hudsonicus grahamensis; MGRS) is among the most critically endangered mammals in the United States and is isolated on the periphery of the species’ range, potentially increasing its conservation priority. To investigate potential threats to the population and provide a tool for land managers, we developed a spatially explicit population dynamics model. We tested model predictions using available range-wide data from the literature and field work specific to the MGRS. A general model input data set using mean life history values overpredicted MGRS abundance. However, we found significant correlation with known squirrel abundance using a general data set with curtailed fecundity and survival. A model with MGRS-specific data provided the best fit to observed population size. We investigated potential impacts of two major threats to the MGRS: competition from introduced Abert’s squirrels (Sciurus aberti) and increased levels of predation. Predation and particularly competition could have significant effects on the future population of the MGRS. Careful attention must be used to model the viability of fringe populations as peripheral populations can have a different life history than populations found in the range core.     

Integration of multiple soil parameters to evaluate soil quality: a field example

Development of a method to assess and monitor soil quality is critical to soil resource management and policy formation. To be useful, a method for assessing soil quality must be able to integrate many different kinds of data, allow evaluation of soil quality based on alternative uses or definitions and estimate soil quality for unsampled locations. In the present study we used one such method, based on non-parametric geostatistics. We evaluated soil quality from the integration of six soil variables measured at 220 locations in an agricultural field in southeastern Washington State. We converted the continous data values for each soil variable at each location to a binary variable indicator transform based on thresholds. We then combined indicator transformed data for individual soil variables into a single integrative indicator of soil quality termed a multiple variable indicator transform (MVIT). We observed that soil chemical variables, pools of soil resources, populations of microorgansims, and soil enzymes covaried spatially across the landscape. These ensembles of soil variables were not randomly distributed, but rather were systematically patterned. Soil quality maps calculated by kriging showed that the joint probabilities of meeting specific MVIT selection were influenced by the critical threshold values used to transform each individual soil quality variable and the MVIT selection criteria. If MVIT criteria adequately reflect soil quality then the kriging can produce maps of the probabilty of a soil being of good or poor quality.     

Leptin regulates striatal regions and human eating behavior

Studies of the fat-derived hormone leptin have provided key insights into the molecular and neural components of feeding behavior and body weight regulation. An important challenge lies in understanding how the rewarding properties of food interact with, and can override, physiological satiety signals and promote overeating. We used functional magnetic resonance imaging to measure brain responses in two human patients with congenital leptin deficiency who were shown images of food before and after 7 days of leptin replacement therapy. Leptin was found to modulate neural activation in key striatal regions, suggesting that the hormone acts on neural circuits governing food intake to diminish the perception of food reward while enhancing the response to satiety signals generated during food consumption.     

Chiral fiber gratings

Chiral gratings with double helix symmetry were produced by twisting glass optical fiber with a noncircular core cross section as it passed through a miniature oven. We observed polarization-selective transmission in chiral fibers with pitches of tens of micrometers. Two modes of optical interaction were differentiated. In chirallong-period gratings, dips in transmission were observed at wavelengths associated with scattering into distinct cladding modes mediated by the chiral grating. In chiral intermediateperiod gratings, a broad scattering band was observed. These gratings can be used to produce sharp or broad polarization-selective filters.