Inheritance and heritability of resistance to citrus leprosis

ABSTRACT The genetic inheritance of resistance to leprosis, the most important viral disease of citrus in Brazil, was characterized through the phenotypic assessment of 143 hybrids resulting from crosses between tangor 'Murcott' (Citrus sinensis x C. reticulata) and sweet orange 'Pêra' (C. sinensis), considered to be resistant and susceptible to the disease, respectively. All plants were grafted onto Rangpur lime (C. limonia) and inoculated with Citrus leprosis virus, cytoplasmic type through the infestation with viruliferous mites, Brevipalpus phoenicis. The experiments were arranged in a completely randomized block design with 10 replicates. Incidence and severity of the disease in leaves and stems as well as plant growth parameters (plant height and stem diameter) were recorded for 3 years after the infestation with the viruliferous mites. The average values of all variables were analyzed using principal component analysis, discriminant factorial analysis, estimation of the clonal repeatability coefficients, and frequency of the distributions of the average values for each measured variable. The principal component analysis resulted in the identification of at least two groups with resistance and susceptibility to leprosis, respectively. About 99% of all hybrids were correctly classified according to the discriminant factorial analysis. The broad-sense heritability coefficients for characteristics associated with incidence and severity of leprosis ranged from 0.88 to 0.96. The data suggest that the inheritance of resistance to leprosis may be controlled by only a few genes.     

Sources of Salmonella contamination during broiler production in Eastern Spain

Prevention of Salmonella contamination of poultry products requires detailed knowledge of the main sources associated with its presence in the production system. The aims of this study were to determine the main sources of Salmonella contamination in broiler production during growing, to assess the risk factors for Salmonella contamination at the end of the rearing period and to determine the main serovars involved in broiler production systems in Eastern Spain. A total of 65 different broiler houses from different farms were sampled. Each house was sampled at different times during the rearing period. First, when the previous flock was taken to the slaughterhouse, samples of dust, surfaces and previous flock faeces were collected. After cleaning and disinfection (C&D), samples of dust and surfaces were also taken. On the first day of rearing, samples of water, bedding, farming boots, meconiums, delivery-box liners and feed were collected. During rearing, feed samples were taken directly from the truck and from feeders. On slaughter day, samples of dust, surfaces, water, feed and faeces were also collected. Finally, two days after slaughter, carriers (rodents, flies and beetles) were trapped. All samples collected were analysed according to ISO 6579:2002 (Annex D) and positive samples were serotyped in accordance with Kauffman-White-Le-Minor technique. Our results showed that all different types of samples collected were contaminated with Salmonella (prevalence ranged between 1.5% and 38.6%). The most contaminated samples related with poultry production were: delivery-box liners (32.0%), faeces samples (31.2%), dust samples (25.0%), farming boots (19.7%) and feed from feeders (16.0%). However, the most important risk factors for Salmonella contamination of the flocks at the end of the rearing period were Salmonella status of the house after cleaning and disinfection, Salmonella status of day-old chick flocks and feed from feeders. Twenty-one different serovars were isolated from the samples analysed. The most prevalent were in decreasing order: Salmonella Enteritidis (52.9%), S. Hadar (17.8%), S. Virchow (8.9%) and S. Ohio (5.4%). The study suggested that there are many sources for Salmonella contamination and persistence in broiler production. Hence, the whole production chain needs to be controlled to eradicate the bacteria from primary production.     

Digital cushions in horses comprise coarse connective tissue, myxoid tissue, and cartilage but only little unilocular fat tissue

Digital cushions were studied in horses with particular reference to vascularization, tissue constituents and matrix components. The cushions mainly resembled a network of coarse collagen bundles. The areas inbetween the bundles were replenished with loosely woven interstitial connective tissue, myxoid tissue, and fibrocartilage. Expected masses of fat lobules were missing: only solitary adipocytes or small groups of adipocytes were seen. Vascular supply to the cushions was remarkably poor. The mucinous myxoid matrix largely consisted of hyaluronan with little sulphated glycosaminoglycans. Myxoid cells were stellate or ramified in shape and showed a tendency to store glycogen and lipid droplets. Myxoid cells reacted for vimentin and stained for S-100 protein. Moreover, myxoid cells often reacted for neuron specific enolase and glial fibrillary acidic protein. Myxoid tissue continuously transformed into loosely organized interstitial connective tissue with fibroblasts, which remained unreactive when tested for neuroectodermal markers. Myxoid tissue also was not clearly demarcated against irregularly interspersed islets of fibrocartilage or hyaline cartilage. Chondrocytes did not stain for neuron specific enolase but reactivity for S-100 protein and glial fibrillary acidic protein was noted in peripheral regions of fibrocartilage. Single or grouped unilocular fat cells were rarely placed into myxoid areas. Unilocular fat cells stained for vimentin, S-100 protein, and occasionally for glial fibrillary acidic protein but not for neuron specific enolase. Continuous transformation of myxoid tissue into cartilage together with corresponding reactivity for neuroectodermal marker proteins of myxoid cells and peripherally located chondrocytes suggest close relationship between myxoid cells and chondrocytes. The same criteria indicate relationship between myxoid cells and adipocytes. Coarse connective tissue, myxoid tissue, fibrous cartilage, and fat cells are functionally combined to absorb mechanical shock in the horse digital cushions.     

Temporal disease dynamics and relative importance of sexual and asexual reproduction of grape downy mildew (Plasmopara viticola) in an isolated vineyard in the North Georgia Mountains,USA

The North Georgia Mountains are the southernmost region along the United States East Coast where European wine grapes (Vitis vinifera) are grown commercially. Epidemics of downy mildew, caused by Plasmopara viticola, are frequent and severe, but little is known about the epidemiology and population biology of the pathogen in this region. Disease monitoring in an experimental vineyard from 2015 to 2017 indicated that times of disease onset and progress rates were highly variable across years and cultivars. Oospores were observed microscopically, and simulation with a process-based model indicated presence of conditions favourable for oospore germination in the spring and early summer each year. A total of 409 P. viticola isolates collected over three  years were genotyped with seven microsatellite markers, revealing very high genotypic diversity, which when combined with the observation of oospores is indicative of a sexually reproducing population. Among the 409 isolates, 225 multilocus genotypes (MLGs) were identified, of which 164 were detected only once and 61 were repeated (clonal). Eight MLGs (represented by 28 isolates) were detected across years, suggesting the possibility of asexual overwintering of P. viticola in this region. Across sampling dates, the percentage of isolates belonging to nonrepeated (unique) MLGs ranged from 27.3% to 63.2%. Even towards the end of the annual epidemic, the percentage of isolates in nonrepeated MLGs was still relatively high, around 30%. These MLGs may have originated from oospores germinating late during the growing season, although incomplete sampling at earlier dates and contribution by immigration cannot be fully excluded.     

Effect of dimethylarsenic acid (DMAA) on growth,tissue arsenic,and photosynthesis of rice plants

The effect of dimethylarsenic acid (DMAA) applied to the root on arsenic (As) uptake and concentration, net photosynthesis (Pn), and growth parameters of rice (Oryza sativa L. cv. ‘Mercury') plants was studied. The experiment consisted of four treatments (0, 0.2, 0.8, and 1.6 mg As/L) with four replications in a completely randomized design. The DMAA was applied in nutrient solution as its sodium salt. The solution culture was changed every four days to avoid changes in the As chemical form. Arsenic uptake and concentration in shoot and root increased upon increased DMAA concentration in solution. Upon uptake, DMAA was readily translocated to the shoot. At the two higher rates of DMAA application (0.8 and 1.6 mg As/L), Pn and photosynthetic capacity were significantly decreased in response to tissue As concentration. Leaf area and dry matter production were also significantly reduced at the two higher rates of DMAA. At the lower rate (0.2 mg As/L) of DMAA application, there was no significant reduction in Pn or growth. Dimethylarsenic acid application did not affect nutrient allocation within the rice plant at concentration levels used in this study.     

BODIUM—A systemic approach to model the dynamics of soil functions

The increasing demand for biomass for food, animal feed, fibre and bioenergy requires optimization of soil productivity, while at the same time, protecting other soil functions such as nutrient cycling and buffering, carbon storage, habitat for biological activity and water filter and storage. Therefore, one of the main challenges for sustainable agriculture is to produce high yields while maintaining all the other soil functions. Mechanistic simulation models are an essential tool to fully understand and predict the complex interactions between physical, biological and chemical processes of soils that generate those functions. We developed a soil model to simulate the impact of various agricultural management options and climate change on soil functions by integrating the relevant processes mechanistically and in a systemic way. As a special feature, we include the dynamics of soil structure induced by tillage and biological activity, which is especially relevant in arable soils. The model operates on a 1D soil profile consisting of a number of discrete layers with dynamic thickness. We demonstrate the model performance by simulating crop growth, root growth, nutrient and water uptake, nitrogen cycling, soil organic matter turnover, microbial activity, water distribution and soil structure dynamics in a long-term field experiment including different crops and different types and levels of fertilization. The model is able to capture essential features that are measured regularly including crop yield, soil organic carbon, and soil nitrogen. In this way, the plausibility of the implemented processes and their interactions is confirmed. Furthermore, we present the results of explorative simulations comparing scenarios with and without tillage events to analyse the effect of soil structure on soil functions. Since the model is process-based, we are confident that the model can also be used to predict quantities that have not been measured or to estimate the effect of management measures and climate states not yet been observed. The model thus has the potential to predict the site-specific impact of management decisions on soil functions, which is of great importance for the development of a sustainable agriculture that is currently also on the agenda of the ‘Green Deal’ at the European level.     

'Pink eye' or 'zere oogjes' or keratoconjunctivitis infectiosa ovis (KIO). Clinical efficacy of a number of antimicrobial therapies

In a comparative study the clinical efficacy of five different treatments of keratoconjunctivitis infectiosa ovis (KIO) were tested, namely an intramuscular injection of chloramphenicol base (dosage 15 mg/kg), spiramycin base (Suanovil dosages 10 to 25 mg/kg), oxytetracycline (Engemycine Forte, Terramycin LA, dosages respectively 5 and 10 mg/kg), tiamulin (Dynamutulin, dosage 10 mg/kg) and subcutaneous injection of procaine penicillin G, benzathine penicillin G. and dihydrostreptomycin in the lower eyelid. It appeared from these field trials that spiramycin base, oxytetracycline and tiamulin had a clearly positive effect on the clinical course of 'pink eye', although with tiamulin there was only a temporary effect (high percentage of relapses). In view of the field data the following dosage schemes are, for the time being, advised: spiramycin base (Suanovil), and oxytetracycline (formulation with a good biological availability) both 20 to 30 mg/kg and, if necessary, to be repeated on days 5 and 10 after the first intramuscular injection. The dosage scheme advised for tiamulin is 20-30 mg/kg to be repeated on day 3 and if necessary on days 6 and 9 after the intramuscular injection. In mild cases it is sufficient to rub the eyes with for example oxytetracycline eye-ointment, a few times a day.     

Maedi-visna control in sheep. I. Artificial rearing of colostrum-deprived lambs

A field trial to study the practicability and efficacy of maedi-visna control in sheep by artificial rearing of lambs was carried out during the lambing season of 1979. Lambs were immediately separated from the dams at birth, deprived of ovine colostrum, and reared isolated from the parent flock. Bovine colostrum was given instead of maternal colostrum. Eleven farms participated in the experiment. All flocks were severely infected with maedi-visna virus: 63-100% of the ewes were seropositive as demonstrated by ELISA. Artificially reared lambs were serologically tested and positives culled at the age of 6, 12, 18, 24, 30 and 36 months. Only very few positives were found: 1/389, 1/376, 0/337, 1/223, 1/192 and 0/144, respectively. The first two sero-positive lambs occurred in one flock, and it could be ascertained that both had mistakenly been given ovine colostrum probably containing maedi-visna virus. No explanation, other than sub-optimal hygiene and isolation, could be found for the two sero-positive sheep that turned up in another flock at 24 and 30 months of age although, transplacental infection cannot be entirely excluded. It is concluded that artificial rearing of ovine colostrum-deprived lambs is an effective and practicable method for the control of maedi-visna in sheep. The method appears particularly useful when valuable genetic material has to be salvaged.