Screening techniques and sources of resistance to abiotic stresses in cool-season food legumes

Summary The adaptability and productivity of cool-season food legumes (chickpea, faba bean, lentil, pea) are limited by major abiotic stresses including drought, heat, frost, chilling, waterlogging, salinity and mineral toxicities. The severity of these stresses is unpredictable in field experiments, so field trials are increasingly supplemented with controlled-environment testing and physiological screening. For drought testing, irrigation is used in dry fields and rain-out shelters in damp ones. Carbon isotope discrimination (Δ¹³C) is a well-established screen for drought tolerance in C3 cereal crops which is now being validated for use in grain legumes, but it is relatively expensive per sample and more economical methods include stomatal conductance and canopy temperature. Chickpea lines ICC4958 and FLIP87-59C and faba bean line ILB938 have demonstrated good drought tolerance parameters in different experiments. For frost tolerance, an efficient controlled-environment procedure involves exposing hardened pot-grown plants to sub-zero temperatures. Faba beans Cote d’Or and BPL4628 as well as lentil ILL5865 have demonstrated good freezing tolerance in such tests. Chilling-tolerance tests are more commonly conducted in the field and lentil line ILL1878 as well as derivatives of interspecific crosses between chickpea and its wild relatives have repeatedly shown good results. The timing of chilling is particularly important as temperatures which are not lethal to the plant can greatly disrupt fertilization of flowers. Salinity response can be determined using hydroponic methods with a sand or gravel substrate and rapid, efficient scoring is based on leaf symptoms. Many lines of chickpea, faba bean and lentil have shown good salinity tolerance in a single article but none has become a benchmark. Waterlogging tolerance can be evaluated using paired hydroponic systems, one oxygenated and the other de-oxygenated. The development of lysigenous cavities or aerenchyma in roots, common in warm-season legumes, is reported in pea and lentil but is not well established in chickpea or faba bean. Many stresses are associated with oxidative damage leading to changes in chlorophyll fluorescence, membrane stability and peroxidase levels. An additional factor relevant to the legumes is the response of the symbiotic nitrogen-fixing bacteria to the stress.     

Pollination, Fertilization and Seed Development in Inbred Lines and F1 Hybrids of Spring Faba Beans (Vicia faba L.)

When the flowers are not disturbed, the yield of F₁ hybrids of faba beans normally exceeds that in their inbred parents. The basis of this “heterotic autofertility” was investigated by examining flowers for pollination and fertilization throughout the flowering season and assessing the distribution of seeds and pods on mature plants. Six inbred lines and seven of their F₁ hybrids were grown without protection from bee visitation, and their autofertility was estimated’ by comparing their fertilization with that of cytoplasmic male-sterile line. The first direct evidence was obtained that heterotic autofertility acts by increasing; the proportion of flowers which were pollinated and fertilized. The autofertility was not perfect, especially in a closed-flower hybrid, as many ovules remained unfertilized. Several factors contributed to the number of seeds per pod in F₁ hybrids, being superior to parental means: (1) more ovules per flower, (2) greater fertilization of the basal ovules, (3) reduced abortion of the apical ovules and (4) greater overall maturation ovules.     

Assessment of Nitrogen Leaching at ICP-Waters Sites (Europe and North America)

The International Cooperative Programme on Assessment and Monitoring of Acidification of Rivers and Lakes (ICP-Waters) is designed to assess the degree and geographical extent of acidification of surface waters. During the last 20 years, international emission reduction measures in Europe and North America have resulted in a decrease in atmospheric S-deposition of up to 50%, while N-deposition has stayed almost constant. Empirical relationships between N-deposition and stages of nitrogen saturation are used to assess the importance of nitrogen leaching at the ICP-Waters sites in Europe and North America. There is a clear coherence between high N saturation stages and high N deposition loads and more than 50% of the analysed ICP Waters sites show a high degree of nitrogen saturation, defined as stages 2 or 3 in Stoddard's classification system. Significant leaching of inorganic N also occurs at most sites with deposition greater than 10 kg/ha/yr.     

Implication of Lake Water Residence Time on the Classification of Norwegian Surface Water Sites into Progressive Stages of Nitrogen Saturation

Seasonal behaviour of NO₃ ^- in surfacewater is often used as an indicator on a catchment's ability toretain N from atmospheric deposition. In this paper, weclassify 12 pristine sites (five streams and seven lakes) insouthernmost Norway according to the N saturation stageconcept. All examined sites were acid-sensitive and had annualmean NO₃ ^- concentrations in the range 6–36 μeqL^-1. At lake sites with relatively long water residencetimes, hydrology will have a damping effect on the seasonalNO₃ ^- oscillations in the outlet streams. Under givenrunoff conditions (1.0–2.2 m yr^-1), the seasonalNO₃ ^- pattern was clearly affected when lake:catchmentarea ratios exceeded 0.15 and the total residence time of lakesin the catchments exceeded 0.3 yr. In such cases, annualmean NO₃ ^- concentration rather than seasonalvariations may be the better indicator of N saturation. Toaccount for this we propose a set of supplementary criteria forsuch lake systems, defining limit values for annual meanNO₃ ^- concentrations within each stage class. Beforebeing applied on a broader scale, however, we recommend anexamination of additional lake-dominated catchmentsrepresenting a larger gradient in ecosystem types, N depositionlevels and hydrologic regimes. When applying the supplementarycriteria on the Norwegian sites, two were classified as stage 0(no saturation), five as stage 1 (early stage of saturation)and five as stage 2 (saturated – moderate N loss). No siteswere showing symptoms of stage 3, which characteriseswatersheds that are net sources of N, rather than sinks. Theresults indicate a great variability in N retention capacity inthe study region, despite the fact that many of the catchmentsexperience relatively uniform N deposition amounts and climaticconditions. This suggests that much of this variability must bedue to specific catchment characteristics as e.g. soil type,soil depth, and vegetation cover.     

Revitalizing the winter turnip rape crop in the northern latitudes

Abstract

Winter turnip rape (Brassica rapa spp. oleifera) is an underutilized crop that deserves to be revitalized for use in high-latitude agriculture. Many crop rotations around the world are dependent on the small-grain cereals, and turnip rape as a break crop, with its range of secondary chemicals, helps to suppress weeds, nematodes and pathogenic fungi. It may be used as an energy crop, it can restrict erosion and nutrient leaching while also improving soil structure and fertility, and it requires relatively low inputs. Although winter turnip rape was once the major oil crop in Finland, in the 1970s it was replaced by spring turnip rape, the lower erucic acid and glucosinolate contents of which made it suitable for food and feed uses. Winter hardiness of the crop could be improved, and industrial end uses, such as lubricants for which high erucic acid content is preferred, targeted in the first instance. Breeding progress would be accelerated by a change from the predominantly self-incompatible breeding system to self-compatibility, now available in modern germplasm, and this would allow use of other rapid breeding methods, such as doubled haploidy. Thus, the many advantages of the winter turnip rape crop would repay its return to agriculture. In this review we will introduce the many utilization possibilities of the crop as well as give background on why more attention and research efforts should be paid towards this crop. We will also indicate some of the array of factors that have a marked role in an attempt to ecologically intensify crop production.     

The crystal structure of TAL effector PthXo1 bound to its DNA target

DNA recognition by TAL effectors is mediated by tandem repeats, each 33 to 35 residues in length, that specify nucleotides via unique repeat-variable diresidues (RVDs). The crystal structure of PthXo1 bound to its DNA target was determined by high-throughput computational structure prediction and validated by heavy-atom derivatization. Each repeat forms a left-handed, two-helix bundle that presents an RVD-containing loop to the DNA. The repeats self-associate to form a right-handed superhelix wrapped around the DNA major groove. The first RVD residue forms a stabilizing contact with the protein backbone, while the second makes a base-specific contact to the DNA sense strand. Two degenerate amino-terminal repeats also interact with the DNA. Containing several RVDs and noncanonical associations, the structure illustrates the basis of TAL effector-DNA recognition.     

The effect of rehabilitation of northern elephant seals (Mirounga angustirostris) on antimicrobial resistance of commensal Escherichia coli

The aim of this study was to determine if antimicrobial drug use increases resistance of commensal gastrointensinal Escherichia coli of wild northern elephant seals (Mirounga angustirostris) treated in rehabilitation, and, if so, identify the risk factors involved. Minimum inhibitory concentration (MIC) levels of twelve antimicrobial drugs were determined for 289 E. coli isolates from 99 seals sampled at admission and 277 isolates obtained at release from rehabilitation using broth microdilution. Prevalence of E. coli antimicrobial resistance, MIC(50), MIC(90), and clustering of MIC values were determined for seals and the data were analyzed using Fisher's exact test, ordinal logistic regression and negative binomial regression. At release from rehabilitation 77.8% of the seals had antimicrobial resistant E. coli compared to 38.4% of the seals at admission. The MIC(90) for amoxicillin-clavulanic acid, chloramphenicol, enrofloxacin, ticarcillin-clavulanic acid, and trimethoprim-saulfamethoxazole were at levels considered to be sensitive at admission but they increased to levels of resistance at release. E. coli were grouped into four clusters by their MIC values, with increasing levels of resistance going from Cluster 1 to 4. A primary risk factor associated with the probability of a seal having E. coli in Clusters 3 and 4 was time in rehabilitation, regardless of whether the animal received treatment with antimicrobial drugs, suggesting nosocomial infection. The results of this study provide evidence that increased levels of hygiene and appropriate use of antimicrobial therapy might be important in the rehabilitation of wild animals to prevent rise in the prevalence of antimicrobial resistant bacteria.