Effects of crop management patterns on coffee rust epidemics

The effects of crop management patterns on coffee rust epidemics, caused by Hemileia vastatrix , are not well documented despite large amounts of data acquired in the field on epidemics, and much modelling work done on this disease. One main reason for this gap between epidemiological knowledge and understanding for management resides in the lack of links between many studies and actual production situations in the field. Coffee rust epidemics are based on a seemingly simple infection cycle, but develop polycyclic epidemics in a season and polyetic epidemics over successive seasons. These higher-level processes involve a very large number of environmental variables and, as in any system involving a perennial crop, the physiology of the coffee crop and how it affects crop yield. Crop management is therefore expected to have large effects on coffee rust epidemics because of its immediate effect on the infection cycle, but also because of its cumulative effect on ongoing and successive epidemics. Quantitative examples taken from a survey conducted in Honduras illustrate how crop management, different combinations of shade, coffee tree density, fertilization and pruning may strongly influence coffee rust epidemics through effects on microclimate and plant physiology which, in turn, influence the life cycle of the fungus. We suggest there is a need for novel coffee rust management systems which fully integrate crop management patterns in order to manage the disease in a sustainable way.     

Simulation modelling of yield losses caused by wheat stem rust

Stem rust, or black rust, of wheat, caused by Puccinia graminis f. sp. tritici, has recently re-emerged in several parts of the world, with epidemics occurring in eastern Africa, as well as northern and southern Europe. Damage mechanisms from disease dynamically affect the physiology of the crop as it grows and develops, and as the epidemic progresses, leading to yield losses in the stem rust-diseased wheat stand. Process-based agrophysiological models that include disease-induced damage mechanisms can help to better understand the physiological processes leading to yield losses, and to inform strategic decisions such as breeding strategies. Such models have not been developed for wheat stem rust so far. Two damage mechanisms for stem rust, light stealing and assimilate diversion, were incorporated in the agrophysiological simulation model WHEATPEST. The model, tested from experimental field data retrieved from the literature, provides a satisfactory representation of the system, although consistently underestimates relative yield losses by about 6.9%, resulting in relative yield losses between 17% and 56%. Analyses highlight the importance of the diversion of assimilates toward the pathogen in the magnitude of yield loss. Considering only the reduction of green leaf area would underestimate damage from stem rust by at least threefold. The analysis also shows the importance of the dynamic interplay between disease and crop growth, especially the dynamics of leaf area, on yield loss. Directions to consider additional damage mechanisms are proposed, and perspectives for future research, especially in relation to plant breeding strategies under climate change, are offered.     

Elution of metronidazole and gentamicin from polymethylmethacrylate beads

OBJECTIVE: To characterize the elution and bioactivity of metronidazole and gentamicin sulfate polymerized, individually and in combination, with polymethylmethacrylate (PMMA). STUDY DESIGN: In vitro experimental study. METHODS: PMMA beads containing metronidazole (3 concentrations), gentamicin sulfate, or metronidazole and gentamicin sulfate were immersed in 5 mL of phosphate-buffered saline in triplicate. Eluent was replaced at specified time intervals for 1 or 21 days, and antibiotic concentrations were measured by high-performance liquid chromatography. Changes in antibiotic bioactivity attributable to polymerization or copolymerization of the antibiotics with PMMA, ethylene oxide sterilization, and storage of AIPMMA beads containing metronidazole were evaluated. RESULTS: Antibiotic elution patterns were similar for all groups. Day 1 elution for groups containing metronidazole or gentamicin individually represented a mean 63%-66% and 79%, respectively, of the 21-day total. Approximately 50% of the day 1 elution occurred during the first hour. The elution of metronidazole was dose dependent. The elution of metronidazole (day 3-21) and gentamicin (all days) was significantly greater when metronidazole and gentamicin were combined (P <.05). The addition of metronidazole delayed polymerization of PMMA. Neither polymerization nor copolymerization of metronidazole and gentamicin with PMMA, gas sterilization, or 2-month storage of beads containing metronidazole significantly affected antimicrobial bioactivity. CONCLUSIONS: Metronidazole elution from PMMA was dose dependent. Copolymerization of metronidazole and gentamicin sulfate in PMMA resulted in increased rates of elution. Intraoperative preparation of metronidazole-impregnated PMMA beads is not practical, but sterilization and storage for 2 months should not affect efficacy. CLINICAL RELEVANCE: The local delivery of biologically active metronidazole and gentamicin by elution from PMMA is feasible.     

Induction of immunity in calves to mycoplasma bovis infection of the respiratory tract

Immunity to colonization of the respiratory tract by Mycoplasma bovis (formerly Mycoplasma agalactiae subsp. bovis was induced in calves by inoculation of formalin inactivated organisms. Animals inoculated intramuscularly and then intratracheally with inactivated mycoplasmas had significantly fewer M. bovis in their lungs, compared with non-vaccinated animals, 3 weeks after intratracheal challenge with viable organisms. In contrast, there was no significant difference in the numbers of M. bovis isolated from the lungs of control animals and of calves given two intramuscular inoculations of inactivated organisms. These results indicate that stimulation of the local immune system is important in the development of resistance to M. bovis respiratory infection following vaccination with inactivated organisms.     

Effects of dietary changes on the antibacterial activity of pancreatic juice in weaned piglets

At weaning, low feed intake level is a major factor responsible for gut disorders. However, less is known on adaptation of the antibacterial activity of pancreatic juice in response to variations in feed intake level. Moreover bovine colostrum has been demonstrated to decrease coliform counts in duodenal digesta and to improve health status of weaned piglets. Aims of the present study were to evaluate effects of feed intake level and of a bovine colostrum-supplemented diet on the pancreatic secretion of antibacterial activity in piglets at weaning. At 33 days of age, twenty-eight piglets fitted with two permanent catheters (for pancreatic juice collection and reintroduction) were weaned and allocated to one of the following three dietary treatments for 5 days: low feed allocation with a starter diet (L), gradually increased feed allocation with a starter diet (Ctrl), or gradually increased feed allocation with a starter diet supplemented with bovine colostrum (Col). In Ctrl piglets, the post-weaning secretion of antibacterial activity did not significantly differed from pre-weaning values. The pancreatic secretion of antibacterial activity in L piglets was higher than that in Ctrl piglets at day 5 (+ 300%; P < 0.05). Moreover in Col piglets the secretion of the antibacterial activity tended to increase by 55% (P = 0.08) compared to Ctrl piglets. Variations in the pancreatic secretion of antibacterial activity could constitute an adaptive phenomenon to maintain bacterial homeostasis in the upper small intestine during the early post-weaning period.     

Pharmacokinetics of transdermal flunixin in sows

The objective of this study was to describe the pharmacokinetics (PK) of flunixin in 12 nonlactating sows following transdermal (TD) flunixin (3.33 mg/kg) and intravenous (IV; 2.20 mg/kg) flunixin meglumine (FM) administration using a crossover design with a 10‐day washout period. Blood samples were collected postadministration from sows receiving IV FM (3, 6, 10, 20, 40 min and 1, 3, 6, 12, 16, 24, 36, and 48 hr) and from sows receiving TD flunixin (10, 20, 40 min and 1, 2, 3, 4, 6, 8, 12, 16, 24, 36, 48, 60, and 72 hr). Liquid chromatography and mass spectrometry were used to determine plasma flunixin concentrations, and noncompartmental methods were used for PK analysis. The geometric mean ± SD area under the plasma concentration–time curve (AUC) following IV injection was 26,820.59 ± 9,033.88 and 511.83 ± 213.98 hr ng/ml for TD route. Mean initial plasma concentration (C₀) was 26,279.70 ± 3,610.00 ng/ml, and peak concentration (C_max) was 14.61 ± 7.85 ng/ml for IV and TD administration, respectively. The percent mean bioavailability of TD flunixin was 1.55 ± 1.00. Our results demonstrate that topical administration is not an efficient route for delivering flunixin in mature sows.