Resistance to rice sheath blight (<Emphasis Type="Italic">Rhizoctonia solani</Emphasis> Kühn) [(teleomorph: <Emphasis Type="Italic">Thanatephorus cucumeris</Emphasis> (A.B. Frank) Donk.] disease: current status and perspectives

Sheath blight (ShB) disease, caused by Rhizoctonia solani, is an economically important rice disease worldwide, especially in intensive production systems. Several studies have been conducted to identify sources for ShB resistance in different species of rice, including local accessions and landraces. To date, none of the genotypes screened are immune to ShB, although variation in levels of resistance have been reported. Several quantitative trait loci (QTL) for ShB resistance have been identified using mapping populations derived from indica or japonica rice. A total of 33 QTL associated with ShB resistance located on all 12 rice chromosomes have been reported, with ten of these co-localizing with QTL for morphological attributes, especially plant height, or for heading date. Sixteen QTL, from the same or differing genetic backgrounds, have been mapped at least twice. Of these, nine QTL were independent of morphological traits and heading date. We hypothesize that two main, distinct, mechanisms contribute to ShB resistance: physiological resistance and disease escape. Strategies to improve our understanding of the genetics of resistance to ShB are discussed.     

Potential of indigenous bradyrhizobia versus commercial inoculants to improve cowpea (Vigna unguiculata L. walp.) and green gram (Vigna radiata L. wilczek.) yields in Kenya

Limited information is available on reduced cowpea (Vigna unguiculata L. Walp.) and green gram (Vigna radiata L.Wilczek.) yields in Kenya. Declining soil fertility and absence or presence of ineffective indigenous rhizobia in soils are assumptions that have been formulated but still require to be demonstrated. In this study, soils were collected from legume growing areas of Western (Bungoma), Nyanza (Bondo), Eastern (Isiolo), Central (Meru) and Coast (Kilifi) provinces in Kenya to assess indigenous rhizobia in soils nodulating cowpea and green gram under greenhouse conditions. Our results showed that highest nodule fresh weights of 4.63 and 3.32?g plant^?1 for cowpea and green gram were observed in one soil from Isiolo and another from Kilifi, respectively, suggesting the presence of significant infective indigenous strains in both soils. On the other hand, the lowest nodule fresh weights of 2.17 and 0.72?g plant^?1 were observed in one soil from Bungoma for cowpea and green gram, respectively. Symbiotic nitrogen (N) fixation by cowpea and green gram was highest in Kilifi soil with values of 98% and 97%, respectively. A second greenhouse experiment was undertaken to evaluate the performance of commercial rhizobial inoculants with both legumes in Chonyi soil (also from Coast province) containing significant indigenous rhizobia [>13.5?×?10³ Colony Forming Units (CFU) g^?1]. Rhizobial inoculation did not significantly (P?相似文献   

Antimicrobial resistance in Campylobacter from broilers: association with production type and antimicrobial use

The isolation and antimicrobial resistance of Campylobacter jejuni and Campylobacter coli strains from broilers arriving in French slaughterhouses, were analysed according to production types (i.e. standard, export or free-range) and antimicrobial (i.e. coccidiostats, growth promoters or therapeutic agents) administration in flocks. Prevalence was 56.6% in standard, 51.3% in export and 80.0% in free-range broilers. Three hundred and ninety-three strains were identified. Two-thirds of the strains belonged to the species C. jejuni. The others were C. coli. Antimicrobial susceptibility testing was carried out for ampicillin, nalidixic acid, enrofloxacin, tetracycline, erythromycin and gentamicin according to a dilution method. The percentages of resistant strains were, 23, 25, 17, 57, 0.3 and 0% for C. jejuni and 29, 43, 40, 70, 31 and 0% for C. coli. Statistical analysis revealed significant difference in distribution of C. jejuni and C. coli and antimicrobial resistance according to production type or antimicrobial administration.     

Research priorities for rice pest management in tropical Asia: a simulation analysis of yield losses and management efficiencies

ABSTRACT A simulation study was conducted to assess the current and prospective efficiency of rice pest management and develop research priorities for lowland production situations in tropical Asia. Simulation modeling with the RICEPEST model provided the flexibility required to address varying production situations and diverse pest profiles (bacterial leaf blight, sheath blight, brown spot, leaf blast, neck blast, sheath rot, white heads, dead hearts, brown plant-hoppers, insect defoliators, and weeds). Operational definitions for management efficacy (injury reduction) and management efficiency (yield gain) were developed. This approach enabled the modeling of scenarios pertaining to different pest management strategies within the agroecological contexts of rice production and their associated pest injuries. Rice pests could be classified into two broad research priority-setting categories with respect to simulated yield losses and management efficiencies. One group, including weeds, sheath blight, and brown spot, consists of pests for which effective pest management tools need to be developed. The second group consists of leaf blast, neck blast, bacterial leaf blight, and brown plant-hoppers, for which the efficiency of current management methods is to be maintained. Simulated yield losses in future production situations indicated that a new type of rice plant with high-harvest index and high-biomass production ("New Plant Type") was more vulnerable to pests than hybrid rice. Simulations also indicated that the impact of deployment of host resistance (e.g., through genetic engineering) was much larger when targeted against sheath blight than when targeted against stem borers. Simulated yield losses for combinations of production situations and injury profiles that dominate current lowland rice production in tropical Asia ranged from 140 to 230 g m(-2). For these combinations, the simulated efficiency of current pest management methods, expressed in terms of relative yield gains, ranged from 0.38 to 0.74. Overall, the analyses indicated that 120 to 200 x 10(6) tons of grain yield are lost yearly to pests over the 87 x 10(6) ha of lowland rice in tropical Asia. This also amounts to the potential gain that future pest management strategies could achieve, if deployed.     

Otopathy secondary to trigeminal schwannoma in a Quarter Horse

Otitis media secondary to trigeminal nerve (CN-V) paralysis is described in dogs and humans but not in horses. An 18-month-old Quarter Horse colt was presented with history of mastication difficulties and a nonhealing corneal ulcer. Clinical findings were consistent with paralysis of the right CN-V. Computed tomography imaging showed otopathy media and a mass at the root of the CN-V. The colt was euthanised due to poor prognosis. Post-mortem magnetic resonance imaging showed enlargement of the right CN-V which was slightly hyperintense on T2W. Histopathology of the mass revealed fusiform tumoural cells, positive on vimentin- and S100 immunohistochemistry, consistent with a schwannoma. Otitis media was presumed secondary to CN-V paralysis and denervation of the right tensor veli palatini muscle involved in opening of the Eustachian tube. This is the first case of trigeminal schwannoma and secondary otopathy media described in a horse, which highlights the importance of imaging in investigating trigeminal nerve paralysis.     

Synthesis and antimicrobial activity of geranyloxy- and farnesyloxy-acetophenone derivatives against oral pathogens

The compounds 2',6'-dihydroxy-4'-geranyloxyacetophenone (1) and 2',6'-dihydroxy-4'-farnesyloxy-acetophenone (2) are oxyprenylated secondary metabolites extracted from plants belonging to the Rutaceae family. In this study, 1 and 2 were synthesized and tested for their antimicrobial activity toward major oral pathogens. Compounds 1 and 2 were synthesized by selective prenylation of 2,4,6-trihydroxyacetophenone at the 4' position with geranyl and farnesyl bromide, respectively. Compound 1 showed stronger antimicrobial activity than 2 against major oral pathogens, including Gram positive bacteria (Streptococcus mutans, Streptococcus sobrinus), Gram negative bacteria (Prevotella intermedia, Porphyromonas gingivalis) and Candida albicans. Evidences were obtained that the mode of action of 1 and 2 may be related to their iron-chelating property. This study suggests that 1 and 2 may represent potential natural molecules for the prevention/treatment of common oral infections, including dental caries, periodontal disease, and candidiasis.     

Contribution to the Understanding of Unexplained Death of Pasturing Horses in the North of Spain: A Retrospective Case Series

The aim of this work was to study a retrospective case series of acute degenerative myopathy, which caused high mortality in adult horses grazing in a specific region of Spain, in relation to a possible etiopathogenesis. Outbreaks of myopathy occurred in December of 1999, 2003, 2009, and 2011 after an abrupt fall in temperatures and the first snowfalls. Ten horses were necropsied, and an exhaustive gross and histopathological examination was performed using specific histochemical stainings to evaluate muscle and cardiac damage. Intense myodegeneration, affecting the postural and respiratory muscles and the muscles involved in swallowing, was the main finding. A further consistent finding was necrosis of Purkinje fibers in the myocardium. Serum concentration values of creatine kinase, selenium, and vitamin E, as well as blood concentration values of glutathione peroxidase activity, were determined in 10 horses clinically affected and in another 12 horses with no clinical signs. In the affected horses, creatine kinase was high and reached values over 10,000 U/L. Selenium values were deficient in the horses affected, ranging from 4.2 to 10.5 μg/g (reference range: >50 μg/L) in selenium-untreated horses, and also, selenium values in 11 horses with no clinical signs were below the reference range. Glutathione peroxidase activity was below the reference range in all the analyzed sera, and vitamin E values were also below the reference range in four horses. The severe selenium deficiency together with a sudden arrival of unfavorable weather conditions seemed to provoke the arising of this disease. The presence of Eupatorium cannabinum in this valley is discussed as a possible source of the phytotoxin associated with rhabdomyolysis.