Microsatellite mapping of powdery mildew resistance allele <Emphasis Type="Italic">Pm5d</Emphasis> from common wheat line IGV1-455

The powdery mildew resistance allele Pm5d in the backcross-derived wheat lines IGV1-455 (CI10904/7*Prins) and IGV1-556 (CI10904/7*Starke) shows a wide spectrum of resistance and virulent pathotypes have not yet been detected in Germany. Although this allele may be distinguished from the other documented Pm5 alleles by employing a differential set of Blumeria graminis tritici isolates, the use of linked molecular markers could enhance selection, especially for gene pyramiding. Pm5d was genetically mapped relative to six microsatellite markers in the distal part of chromosome 7BL using 82 F₃ families of the cross Chinese Spring × IGV1-455. Microsatellite-based deletion line mapping placed Pm5d in the terminal 14% of chromosome 7BL. The closely linked microsatellite markers Xgwm577 and Xwmc581 showed useful variation for distinguishing the different Pm5 alleles except the ones originating from Chinese wheat germplasm. Their use, however, would be limited to particular crosses because they are not functional markers. The occurrence of resistance genes closely linked to the Pm5 locus is discussed. Ghazaleh Nematollahi and Volker Mohler equally contributed to this work.     

The importance of C,N and P as driver for bacterial community structure in German beech dominated forest soils

Among several environmental factors shaping soil microbial communities the impact of soil nutrients is of special interest. While continuous application mainly of N and P dramatically shifts community composition during fertilization, it remains unclear whether this effect is consistent in generic, unfertilized beech forest ecosystems of Germany, where differences in nutrient contents are mostly a result of the parental material and climatic conditions. We postulate that in such ecosystems nutrient effects are less pronounced due to the possibility of the soil microbiome to adapt to the corresponding conditions over decades and the vegetation acts as the major driver. To test this hypothesis, we investigated the bacterial community composition in five different German beech dominated forest soils, representing a natural gradient of total‐ and easily available mineral‐P. A community fingerprinting approach was performed using terminal‐Restriction Fragment Length Polymorphism analysis of the 16S rRNA gene, while abundance of bacteria was measured applying quantitative real‐time PCR. Bacterial communities at the five forest sites were distinctly separated, with strongest differences between the end‐members of the P‐gradient. However the majority of identified microbial groups (43%) were present at all sites, forming a core microbiome independent from the differences in soil chemical properties. Especially in the P‐deficient soil the abundance of unique bacterial groups was highly increased, indicating a special adaption of the community to P limitation at this site. In this regard Correspondence Analysis elucidated that exclusively soil pH significantly affected community composition at the investigated sites. In contrast soil C, N and P contents did mainly affect the overall abundance of bacteria.     

The Potential of Semiochemicals for Control of Phorodon humuli (Homoptera: Aphididae)

Field experiments employing yellow water-traps with vials releasing methyl salicylate, butyl isothiocyanate, 4-pentenyl isothiocyanate and diethyltoluamide were conducted during the spring migration of Phorodon humuli (Schrank), with the aim of identifying substances which might be used in the field to deter landing on hop plants. Methyl salicylate and the two isothiocyanates reduced trap catches of P. humuli. During the spring of 1994 a slow-release formulation of methyl salicylate and a β-acid-rich hop resin sprayed on to hop plants did not reduce aphid infestations significantly. In autumn cis,cis-nepetalactol, the main component of P. ‘humuli’s sex pheromone, prepared by various synthetic routes, increased trap catches of males and gynoparae equally. Catches of males in pheromone traps situated in a hop garden decreased with increasing trap height. Catches of males in traps charged with increasing doses of the cis,cis-nepetalactol peaked at 1 mg and then plateaued, whereas catches of gynoparae peaked similarly at 1 mg and then decreased. The effects of kairomones from an extract of the primary host, sex pheromone and a visual cue from yellow compared with clear water-traps were additive. The prospects for developing a semiochemicals-based control strategy against P. humuli, using some or all of the above elements, are discussed.     

Arsenic in field‐collected soil solutions and extracts of contaminated soils and its implication to soil standards

Large concentrations of arsenic in soils, sediments, and freshwaters require risk assessment across the Central Alps and other regions. We measured arsenic concentrations in soil samples collected from 38 sites located in the Austrian Central Alps that had been contaminated due to mining and smelter activities and geogenic mineralization. Medians and ranges of arsenic concentrations (in mg kg^—1) in the soil solid phase were: 77.1 (1—3000) for the total (As_t), 19.2 (0—726) for (NH₄)₂C₂O₄‐extractable (As_o), 2.35 (0—169) for (NH₄)₂HPO₄‐extractable (As_p), and 0.143 (0—11.1) for (NH₄)₂SO₄‐extractable (As_s) arsenic. Arsenic concentrations in soil solutions (As_sol) collected from organic surface layers and mineral horizons at five selected sites using suction cups fitted with nylon membranes ranged from 0 to 171 μg l^—1. Typically, the prevailing species of As in the soil solution was As(V). As_sol was correlated with As_s (As_sol = 0.279 + 15.6 As_s; r² = 0.938; n = 17) and As_t (As_sol = 1.272 + 0.043 As_t; r² = 0.833; n = 17). Using these empirical models, As_sol can be predicted quite accurately based on extraction with 0.05 M (NH₄)₂SO₄ or total arsenic concentrations in the soil. Linking these models to drinking water standards (DWS) we propose soil standards for freshwater protection that vary for As_s (mg kg^—1) between 0.62 (for DWS = 10 μg l^—1 WHO) and 3.19 (for DWS = 50 μg l^—1). Corresponding standards for As_t (mg kg^—1) are 203 (DWS = 10 μg l^—1) and 1133 (DWS = 50 μg l^—1). These considerations demonstrate that changes in legislation on DWS may have dramatic impact on As concentrations in soil that are acceptable for groundwater protection.     

QTL mapping of improving forage maize starch degradability in European elite maize germplasm

Improving maize starch content is of great importance for both forage and grain yield. In this study, 13 starch degradability traits were analysed including percentage of the seedling area, floury endosperm, hard endosperm of total grain area, percentage of the floury endosperm surface and vitreousness ratio surface hard: floury endosperm surface, etc. We mapped quantitative trait loci (QTL) in a biparental population of 309 doubled haploid lines based on field phenotyping at two locations. A genetic linkage map was constructed using 168 SSR (simple sequence repeat) markers, which covered 1508 cM of the maize genome, with an average distance of 9.0 cM. Close phenotypic and genotypic correlations were found for all traits, and were all statistically significant (p = 0.01) at two locations. Major QTL for more than two traits were detected, especially in two regions in bins 4.05–4.06 and 7.04–7.05, associated with 13 and 9 traits, respectively. This study contributes to marker‐assisted breeding and also to fine mapping candidate genes associated with maize starch degradability.