Synergism in fungicide mixtures againstPseudoperonospora Cubensis

Mixtures of cymoxanil with mancozeb (Mancur) or with mancozeb plus oxadixyl (Pulsan, Sandocur-M) were effective in controlling either metalaxyl-sensitive (MS) or -resistant (MR) isolates ofPseudoperonospora cubensis on cucumbers (cv. ‘Elem’) in growth chambers. Metalaxyl+mancozeb (Ridomil-MZ) and oxadixyl+mancozeb (SAN-518) mixtures were effective against the metalaxyl-sensitive but less so against the metalaxyl-resistant isolate. Fungicide mixtures were far more effective in controlling either the sensitive or the resistant isolates than were the individual components applied alone, thereby representing significant levels of synergistic interactions. Increased efficacy of mixtures relative to their combined components (synergy factor) was calculated by the Wadley method. Mixtures containing cymoxanil showed high synergy factors against the resistant isolate, whereas Ridomil-MZ and SAN-518 did not evince this phenomenon. We concluded that cymoxanil mixtures might be suitable for the control of downy mildew incited by a metalaxyl-resistant isolate ofP. cubensis.     

Accelerating invasion rate in a highly invaded estuary

Biological invasions are a major global environmental and economic problem. Analysis of the San Francisco Bay and Delta ecosystem revealed a large number of exotic species that dominate many habitats in terms of number of species, number of individuals and biomass, and a high and accelerating rate of invasion. These factors suggest that this may be the most invaded estuary in the world. Possible causes include a large number and variety of transport vectors, a depauperate native biota, and extensive natural and anthropogenic disturbance.     

Reverse diel vertical migration: an escape from invertebrate predators

The marine copepod Pseudocalanus sp. exhibits an unusual reverse diel vertical migration in Dabob Bay, Washington, concurrently with a normal vertical migration by nocturnal invertebrate predators. Reduced spatial overlap with predators appears to decrease mortality rate of adult female Pseudocalanus. A life table analysis suggests that the demographic disadvantage associated with daily migration across a thermal gradient can be overcome if mortality is reduced by as little as 16 percent.     

Cytokine expression by neutrophils of adult horses stimulated with virulent and avirulent Rhodococcus equi in vitro

Rhodococcus equi is an intracellular pathogen of macrophages that causes rhodococcal pneumonia in foals and immunocompromised people. Evidence exists that neutrophils play a vital role in resistance to infection with R. equi; however, the means by which neutrophils exert their effects have not been clearly defined. In addition to directly killing bacteria, neutrophils also may exert a protective effect by linking innate and adaptive immune responses. In the present study we evaluated the cytokine expression profiles of adult equine neutrophils in response to stimulation with isogenic strains of virulent and avirulent R. equi in vitro. After 2 and 4 h incubation with virulent or avirulent R. equi, adult equine neutrophils expressed significantly (P < 0.05) greater tumor necrosis factor alpha (TNFα), interleukin (IL)-12p40, IL-6, IL-8 and IL-23p19 mRNA, but not interferon gamma (IFNγ) or IL-12p35 mRNA than unstimulated neutrophils. Furthermore, virulent R. equi induced significantly greater IL-23p19 mRNA than avirulent R. equi. These results demonstrate that R. equi-stimulated neutrophils are a source of many proinflammatory cytokines. Furthermore, these results suggest that IL-23 may be preferentially expressed over IL-12 in response to exposure with R. equi, and that this response may be more strongly induced by virulent R. equi than avirulent R. equi. Collectively, the data presented herein suggest a non-phagocytic role for neutrophils that may influence the type of adaptive immune response to R. equi.     

Evaluation of equine breeding farm characteristics as risk factors for development of Rhodococcus equi pneumonia in foals

OBJECTIVE: To identify farm characteristics as risk factors for the development of Rhodococcus equi pneumonia in foals. DESIGN: Prospective matched case-control study. ANIMALS: 2,764 foals on 64 equine breeding farms with 9,991 horses. PROCEDURE: During 1997, participating veterinarians completed paired data collection forms, 1 for a farm with > or = 1 foal with R equi pneumonia and 1 for an unaffected control farm. Matched data were compared by use of conditional logistic regression analysis. RESULTS: Farm characteristics found in bivariate analyses to be associated with increased risk for pneumonia caused by R equi in foals included > 200 farm acres, > or = 60 acres used in the husbandry of horses, > 160 horses, > or = 10 mares housed permanently on the farm (resident mares), > 17 foals, > 0.25 foals/acre, and the presence of transient mares (mares brought temporarily to the farm for breeding or foaling) and their foals. Affected farms were significantly more likely to be > 200 acres in size and have > or = 10 resident dam-foal pairs, whereas control farms were significantly more likely to have > or = 75% of their dam-foal pairs housed permanently on the farm. CONCLUSIONS AND CLINICAL RELEVANCE: Breeding farms with large acreage, a large number of mares and foals, high foal density, and a population of transient mares and foals are at high risk for foals developing pneumonia caused by R equi.     

Endophytic-Host Selectivity of Discula umbrinella on Quercus alba and Quercus rubra Characterized by Infection, Pathogenicity and Mycelial Compatibility

The fungal endophytic–host relationships of Discula umbrinella and two oak species, Quercus alba and Quercus rubra, were characterized on the basis of endophytic infection, pathogenicity, and mycelial compatibility. Isolates of D. umbrinella were cultured from leaves of Q. alba and Q. rubra collected from a hardwood forest located in Patuxent Wildlife Research Center in Laurel, Maryland, USA. Endophytic infection was observed on sterile leaf discs and living 2-month-old seedlings of Q. alba and Q. rubra. Fungal-host reciprocal inoculations revealed the presence of conidiomata on both hosts but conidiomata production was more abundant on Q. alba. Isolates from Q. rubra produced milder disease symptoms on both oak species. Mycelial compatibility studies identified seven different MCG groups. MCG groups 1–3 contained isolates from both oak species whereas MCG groups 4–7 contained host specific isolates. Field studies monitored the seasonal appearance of the sexual fruiting structures, perithecia, as a possible source of new genetic variation that might alter host specificity/pathogenicity of the D. umbrinella isolates on Q. alba and Q. rubra hosts. Only 1–2% of the leaves contained perithecia throughout the sampling period (April–September). Isolates collected from Q. alba differed from those collected from Q. rubra in endophytic infection, pathogenic response, and perithecia production. The results of this study suggest that the endophyte–host relationship is one of host selective preference for Q. alba, but that the endophyte has the ability to maintain the endophytic/pathogenic life cycle on the less preferred host species, Q. rubra.     

Musculoskeletal problems associated with lameness and poor performance among horses used for barrel racing: 118 cases (2000-2003)

OBJECTIVE: To identify types of musculoskeletal problems associated with lameness or poor performance in horses used for barrel racing. DESIGN: Retrospective case series. ANIMALS: 118 horses. PROCEDURE: Medical records were reviewed for information on signalment, history, physical and lameness examination findings, diagnostic tests performed, diagnosis, and treatment. RESULTS: Most horses were examined because of lameness (n = 72 [61%]) rather than poor performance (46 [39%]), but owner complaint was not significantly associated with age or body weight of the horse. The most common performance change was refusal or failure to turn properly around the first barrel (19/46 [41%]). The right forelimb (n = 57 [48%]) was most commonly affected, followed by the left forelimb (51 [43%]), the left hind limb (31 [26%]), and the right hind limb (25 [21%]). In 31 horses (26%), both forelimbs were affected, and in 6 (5%), both hind limbs were affected. The most common musculoskeletal problems were forelimb foot pain only (n = 39 [33%]), osteoarthritis of the distal tarsal joints (17 [14%]), suspensory ligament desmitis (15 [13%]), forelimb foot pain with distal tarsal joint osteoarthritis (11 [9%]), and bruised feet (10 [8.5%]). In 81 (69%) horses, the affected joint was treated with intra-articular medications. CONCLUSIONS AND CLINICAL RELEVANCE: Results suggest that in horses used for barrel racing that are examined because of lameness or poor performance, the forelimbs are more likely to be affected than the hind limbs, with forelimb foot pain and osteoarthritis of the distal tarsal joints being the most common underlying abnormalities.     

Comparative efficacy of systemic acquired resistance-inducing compounds against rust infection in sunflower plants

ABSTRACT Four inducers of systemic acquired resistance (SAR) were examined for their efficacy in controlling rust infection caused by Puccinia helianthi in sunflower plants. Of the four compounds, DL-3-amino-n-butanoic acid (DL-beta-aminobutyric acid [BABA]) was the most effective and sodium salicylate (NaSA) was the least effective in protecting against rust. In leaf disk assays, full protection was obtained with BABA at 25 mug/ml, benzodiathiazol-S-methyl ester (BTH) at 100 mug/ml, 2,6-di-chloroisonicotinic acid (INA) at 100 mug/ml, and NaSA at >200 mug/ml. L-2-amino-n-butanoic acid (AABA) was partially effective, whereas N-methyl-BABA and 4-aminobutnoic acid (GABA) were ineffective. The R-enantiomer of BABA, but not the S-enantiomer, was more effective than the racemic mixture. In intact plants, BABA applied as a foliar spray or a root dip, before or after (up to 48 h) inoculation, provided significant protection for 8 days. BTH, INA, and NaSA were less protective and more phytotoxic compared with BABA. BABA did not affect urediospore germination, germ tube growth, appressorial formation, or initial ingress of P. helianthi, but strongly suppressed mycelial colonization in the mesophyll and, consequently, pustule and urediospore formation. No accumulation of defense compounds (phenolics, lignin, or callose) was detected in BABA-treated inoculated or noninoculated plants. This is the first report on the activity of BABA against an obligate Basidomycete pathogen in planta.