Morphological Deformities in Chironomus Riparius Meigen Larvae after Exposure to Cadmium over Several Generations

In order to test the potential of chironomiddeformities for biomonitoring, induction of morphologicaldeformities in Chironomus riparius larvae was assessed afterchronic exposure (static with renewal) of eggs and subsequentinstars to sublethal nominal cadmium concentrations of 0, 3 (NOEC),9 (intermediate) and 27 (chronic _LC50) μg Cd l^-1 during 7to 10 generations. Deformities which could be associated with anindirect or direct cadmium effect were split medial mentum teeth(more frequent in 9 and 27 μg Cd l^-1) and premandibledeformities (especially in 3 μg Cd l^-1). The controlcontained more larvae with additional teeth in mentum and mandiblethan the metal-exposed conditions. In the 9 μg Cd l^-1 condition the frequencies of larvae with split medial mentumteeth increased in the last four generations, to reach 40%. Theunpredictability of fluctuations of deformity frequencies over thegenerations was associated with parental effects and experimentalmanipulation. The deformity percentages correlated positively withthe mortalities and could be related to the induction of toleranceto cadmium, as was concluded on the basis of life cycle analysis ina previous paper. This experiment demonstrated a concentration-response relationship between deformities and sublethal levels ofcadmium. However, the observed generation fluctuations caution for(1) the use of single-generation experiments for definingecotoxicological threshold values, and (2) experimentally inducedgenetical drift in multi-generation experiments.     

Phosphorus uptake from struvite is modulated by the nitrogen form applied

Next to nitrogen, phosphorus (P) is the most limiting nutrient for plant production worldwide. To secure food production, new nutrient management strategies using alternative P sources instead of mined P fertilizers need to be implemented. Struvite (MgNH₄PO₄ · 6 H₂O) is a promising example of a recycled mineral P fertilizer. Besides positive agronomic results regarding crop yields, further investigations are required to improve the use efficiency of the product and thereby increase its value. Using an automated plant phenotyping platform, we investigated the dynamic response to struvite by two plant species (lupine and maize) with diverse P acquisition strategies in an acidic sandy substrate. Although at three weeks after germination both maize and lupine had reduced leaf area in the struvite treatments compared to the commercial triple superphosphate (TSP), from week four onwards struvite plants grew larger than the TSP‐treated plants, indicating a slow release fertilizing effect. Greater P uptake efficiency (g / root length), but reduced root length were observed in the combined treatment of struvite and ammonium, in comparison to struvite and nitrate. We propose that rhizosphere acidification in response to ammonium uptake may enhance P recovery from struvite. A possible additional acidification effect by lupine root exudation might explain the higher P uptake efficiency in this species compared to maize. We conclude that struvite combined with ammonium can be used as a sustainable slow‐release P fertilizer on acidic sandy soils.     

Benomyl-resistant Fusarium-isolates in ecological studies on the biological control of fusarium wilt in carnation

Ecological properties and stability of benomyl resistance of three benomyl-resistant mutants of nonpathogenicFusarium-isolates antagonistic to fusarium wilt in carnation, and three benomyl-resistant mutants of a pathogenic isolate ofFusarium oxysporum f.sp.dianthi were evaluatedin vitro and in glasshouse experiments. The benomyl resistance of the nonpathogenic mutants was stable under all conditions tested, also after a 1000-fold increase of the population in sterilized soil. Mutants of the pathogen were stable during allin vitro tests, but after proliferation in carnation stems only part of the population was benomyl resistant.Compared to the wild type, mutants of the pathogen were less pathogenic, also if thein vitro propeties were similar. Colonization of carnation by benomyl-resistant nonpathogenicFusarium in the presence of the pathogen showed that the antagonistic effect correlated with the presence of the nonpathogenic isolates within the carnation stem. The wild types and two of the mutant nonpathogenicFusarium-isolates controlled fusarium wilt in the susceptible cultivar Lena for 50% or more.UV-induced benomyl resistance appeared to be a valuable marker to distinguish between differentFusarium isolates and to study the population dynamics, but intensive screening of the mutants is a prerequisite since alterations in antagonism and pathogenicity can occur.     

A Comparison of Pig Farmers' and Veterinarians' Perceptions and Intentions to Reduce Antimicrobial Usage in Six European Countries

Antimicrobial (AM) resistance is an increasing problem in human and veterinary medicine. To manage this problem, the usage of AM should be reduced in pig farming, as well as in other areas. It is important to investigate the factors that influence both pig farmers' and veterinarians' intentions to reduce AM usage, which is a prerequisite for developing intervention measures. We conducted a mail survey among pig farmers (N = 1,294) and an online survey among veterinarians (N = 334) in Belgium, Denmark, France, Germany, Sweden and Switzerland. The farmers' survey assessed the perceived risks and benefits of and need for AM usage; the intention to reduce AM usage; farmers' efficacy (i.e. perception of their ability to reduce AM usage); support from their veterinarian; and the future reduction potential of AM usage. Additionally, self‐reported reduction behaviours, the perceived farmers' barriers to reduce AM usage and relationships with farmers were assessed in the veterinarians' survey. The results showed that farmers and veterinarians had similar perceptions of the risks and benefits of AM usage. Veterinarians appeared to be more optimistic than pig farmers about reducing AM usage in pig farming. Farmers believed that their efficacy over AM reduction was relatively high. Farmers' intention to reduce AM usage and veterinarians' self‐reported reduction behaviours were mainly associated with factors concerning the feasibility of reducing AM usage. To promote prudent AM usage, pig farmers should learn and experience how to reduce usage by applying alternative measures, whereas veterinarians should strengthen their advisory role and competencies to support and educate farmers.     

Effect of successive cauliflower plantings and Rhizoctonia solani AG 2-1 inoculations on disease suppressiveness of a suppressive and a conducive soil

Disease suppressiveness against Rhizoctonia solani AG 2-1 in cauliflower was studied in two marine clay soils with a sandy loam texture. The soils had a different cropping history. One soil had a long-term (40 years) cauliflower history and was suppressive, the other soil was conducive and came from a pear orchard not having a cauliflower crop for at least 40 years. These two soils were subjected to five successive cropping cycles with cauliflower or remaining fallow in a greenhouse experiment. Soils were inoculated with R. solani AG 2-1 only once or before every crop. Disease decline occurred in all treatments cropped with cauliflower, either because of a decreased pathogen population or increased suppressiveness of the soil. Disease suppressiveness tests indicated that the conducive soil became suppressive after five subsequent cauliflower crops inoculated each cycle with R. solani AG 2-1. Suppressiveness of all treatments was measured in a seed germination test (pre-emergence damping-off) as well as by measuring the spread of R. solani symptoms in young plants (post-emergence damping-off). Results showed that suppressiveness was significantly stimulated by the successive R. solani inoculations; presence of the cauliflower crop had less effect. Suppressiveness was of biological origin, since it disappeared after sterilization of the soil. Moreover, suppressiveness could be translocated by adding 10% suppressive soil into sterilized soil. The suppressive soil contained higher numbers of culturable filamentous actinomycetes than the conducive soil, but treatments enhancing suppressiveness did not show an increased actinomycetes population. The suppressiveness of the soil samples did also not correlate with the number of pseudomonads. Moreover, no correlation was found with the presence of different mycoparasitic fungi, i.e. Volutella spp., Gliocladium roseum, Verticillium biguttatum and Trichoderma spp. The suppressive soil contained a high percentage of bacteria with a strong in vitro inhibition of R. solani. These bacteria were identified as Lysobacter (56%), Streptomyces (23%) and Pseudomonas (21%) spp. A potential role of Lysobacter in soil suppressiveness was confirmed by quantitative PCR detection (TaqMan), since a larger Lysobacter population was present in suppressive cauliflower soil than in conducive pear orchard soil. Our experiments showed that successive cauliflower plantings can cause a decline of the damage caused by R. solani AG 2-1, and that natural disease suppressiveness was most pronounced after subsequent inoculations with the pathogen. The mode of action of the decline is not yet understood, but antagonistic Lysobacter spp. are potential key organisms.     

Moraxella bovis pathogenicity: an update

Moraxella bovis is the etiologic agent of infectious bovine keratoconjunctivitis, the most important ocular disease affecting cattle worldwide. The severity of the cases varied from eyes that exhibited mild signs to severe clinical cases with profuse lacrimation, conjunctival swelling, corneal opacity, and ulceration. Although the mortality is low, there is a high morbidity and important economic loss in terms of significant reduction in production. This paper examines aspects such as the pathogenesis of the disease and the mechanisms by which this unique bacterium is able to disrupt the corneal epithelium and cause infection.     

Soil suppressiveness and functional diversity of the soil microflora in organic farming systems

Arable fields of 10 organic farms from different locations in The Netherlands were sampled in three subsequent years. The soil samples were analysed for disease suppressiveness against Rhizoctonia solani AG2.2IIIB in sugar beet, Streptomyces scabies in radish and Verticillium longisporum in oilseed rape. In addition, a variety of microbial, chemical and physical soil characteristics were assessed. All data were correlated by multiple regression and multivariate analyses with the objective to find correlations between soil suppressiveness and biotic or abiotic soil characteristics. Significant differences in soil suppressiveness were found between the fields for all three diseases. Multiple regression indicated a significant correlation between suppressiveness against Rhizoctonia and the number of antagonistic Lysobacter spp., as well as with % active fungi and bacterial diversity. Grass-clover stimulated Rhizoctonia suppression as well as the presence of antagonistic Lysobacter spp. (mainly L. antibioticus and L. gummosus) in clay soils. Streptomyces suppression correlated with the number of antagonistic Streptomyces spp., % of active fungi and bacterial population size. The presence of antagonistic Streptomyces spp. correlated with a high fungal/bacterial biomass ratio. Verticillium suppression was only measured in 2004 and 2005, due to the inconsistent suppressiveness along the years. Nevertheless, a significant correlation with pH, potential nitrogen mineralization and bacterial biomass was found. Bacterial and fungal PCR-denaturing gel electrophoresis fingerprinting of bacterial and fungal communities, in general, did not significantly correlate with disease suppression. Highly significant explanatory factors of the composition of the dominating bacterial and fungal populations were % lutum, pH, C/N quotient, biomass and growth rate of bacteria. Additionally, the % of organic matter and years of organic farming were explaining significantly the composition of the bacterial population.Thus, significant correlations between several soil characteristics and suppressiveness of different soil-borne pathogens were found. For two of the three pathogens, suppression correlated with biotic soil characteristics combined with the presence of specific bacterial antagonists. Probably the soil suppressiveness measured in the organic fields is a combined effect of general and specific disease suppression.     

Effects of Seven Fungicides on Non-Target Aquatic Fungi

Aquatic risk assessments for fungicides are carried out without information on their toxicity to non-target aquatic fungi. This might cause an underestimation of the toxic effects to the aquatic fungal community. This study focuses on the question whether recently derived concentrations limits for fungicides considered to protect populations of primary producers and (in)vertebrates also do protect the aquatic fungi. A panel of fungal species and Oomycetes was isolated and identified from unpolluted surface waters in the Netherlands. Toxicity tests were used to determine effects of seven fungicides with different modes of actions. For the triazoles epoxiconazole and tebuconazole, the chronic lowest observable effect concentration was lower than the regulatory acceptable concentration based on acute HC5 values.     

Colonisation by arbuscular mycorrhizal and fine endophytic fungi in four woodland grasses – variation in relation to pH and aluminium

Acidic soils are harsh environments for plants. One of the major problems is the potential toxicity of aluminium (Al) and hydrogen ions at a pH below 5; another is the shortage of nutrients usually accompanying soil acidity. The aim of this study was to elucidate the relationship between arbuscular mycorrhizal (AM) colonisation and soil acidity (measured by pH and Al concentration) in order to evaluate the possibility that AM fungi facilitate the existence of plants on acidic soils. We sampled tussocks of four grass species, Elymus caninus, Poa nemoralis, Deschampsia cespitosa and Deschampsia flexuosa, together with samples of the surrounding soil, in oak forests of varying soil pH in southern Sweden. We determined pH, easily reacting Al (Al_r), extractable Al (Al_BaCl2) and phosphate in the soil samples, analysed the shoots for Al and phosphorous and quantified the degree of AM and fine endophyte (FE) colonisation in the roots. E. caninus was found on the least acidic soils and had the highest AM colonisation of all the species studied, while D. flexuosa, which was found on the most acidic soils, had the lowest AM colonisation. P. nemoralis and D. cespitosa were intermediate with respect to pH and AM colonisation. The colonisation of AM fungi exceeded FE colonisation for E. caninus and P. nemoralis, while the opposite was true for the two Deschampsia species. Our results indicated a negative relationship between Al_r and the degree of AM colonisation at the within-species level. The low colonisation of AM fungi on acidic soils may to some extent be explained by a sensitivity of AM fungi to Al_r: this parameter showed a stronger negative association with AM colonisation than did pH and Al_BaCl2. We hypothesize that Al toxicity is a critical factor for plant nutrition in forest soils through the impact on symbiotic fungi.