Evaluation of Olive Cultivars for Resistance to Verticillium dahliae

Resistance of 23 important olive cultivars to Verticillium dahliae has been evaluated in four experiments under controlled conditions. Nine-month-old nursery olive plants were inoculated with a cotton non-defoliating (ND) (V4) or a cotton defoliating (D) (V117) isolate of V. dahliae. Resistance was evaluated by assessing symptom severity using a 0–4 rating scale and estimating the area under disease progress curves. The percentage of plants killed and of those which recovered from the disease were used as additional parameters for including a particular cultivar into a defined category. Most of the evaluated cultivars were susceptible, although at different levels, to both isolates of V. dahliae. All cultivars were more susceptible to the D pathotype than to the ND one. A group of 11 cultivars, including several important Spanish cultivars, were susceptible or extremely susceptible to both pathotypes of V. dahliae. A second group showed differences of resistance depending on the pathotype used. They were susceptible or extremely susceptible to the D pathotype but resistant or moderately susceptible to the ND one. Finally, 'Frantoio', 'Oblonga' and 'Empeltre' were moderately susceptible to the D isolate of V. dahliae and resistant to the ND one. The resistance of 'Empeltre' was evident by the plant ability to recover from infection with either isolates. 'Empeltre' is considered to be a valuable cultivar for inclusion in breeding programmes for resistance to Verticillium wilt.     

Ultrastructural and cytochemical aspects of silicon-mediated rice blast resistance

ABSTRACT Although exogenous application of silicon (Si) confers efficient control of rice blast, the probable hypothesis underlying this phenomenon has been confined to that of a mechanical barrier resulting from Si polymerization in planta. However, in this study, we provide the first cytological evidence that Si-mediated resistance to Magnaporthe grisea in rice correlates with specific leaf cell reaction that interfered with the development of the fungus. Accumulation of an amorphous material that stained densely with toluidine blue and reacted positively to osmium tetroxide was a typical feature of cell reaction to infection by M. grisea in samples from Si+ plants. As a result, the extent of fungal colonization was markedly reduced in samples from Si+ plants. In samples from Si- plants, M. grisea grew actively and colonized all leaf tissues. Cytochemi-cal labeling of chitin revealed no difference in the pattern of chitin localization over fungal cell walls of either Si+ or Si- plants at 96 h after inoculation, indicating limited production of chitinases by the rice plant as a mechanism of defense response. On the other hand, the occurrence of empty fungal hyphae, surrounded or trapped in amorphous material, in samples from Si+ plants suggests that phenolic-like compounds or phytoalexins played a primary role in rice defense response against infection by M. grisea. This finding brings new insights into the complex role played by Si in the nature of rice blast resistance.     

Unravelling the relationships among Verticillium wilt,irrigation, and susceptible and tolerant olive cultivars

Survival, germination, olive colonization, and water-use efficiency (WUE) impairments by Verticillium dahliae could be influenced by cultivar susceptibility or irrigation, and this could modify the irrigation–pathogen–disease relationship. In this study, the combined effects of irrigation and cultivar susceptibility on Verticillium wilt (VW) development were modelled by the temporary assessment of V. dahliae propagules (total inoculum density, density of micropropagules, and sclerotia in wet and air-dried soil; ID, MpD, S_wD, and S_dD, respectively), root (RCI) and shoot (SCI) colonization indexes, and WUE. The relationship of disease severity to the measured parameters was then explored. Under controlled conditions, plants of cultivars ‘Picual’ and ‘Frantoio’ were irrigated to a high and low rate by varying drip-irrigation frequencies: daily, twice weekly, and a combination of daily for 11 days and then twice weekly. Disease severity and colonization parameters were higher in ‘Picual’, while WUE was higher in ‘Frantoio’. However, high rate and twice weekly and combination treatments significantly increased disease incidence and reduced time-to-symptoms-onset only in ‘Picual’, while high rate reduced WUE and increased relative ID, MpD, and S_wD in both cultivars. Irrigation did not affect SCI, but a higher RCI was found at high rate during the development of symptoms in ‘Picual’. By using classification trees to examine parameters—disease severity relationships, it was possible to determine the degree to which VW was affected by irrigation and/or cultivar susceptibility. MpD was the best indicator for VW detection at any time, WUE was best before symptoms developed, and RCI, total ID, and S_dD after symptoms developed.     

Immunodiagnosis of current fasciolosis in sheep naturally exposed to Fasciola hepatica by using a 2.9 kDa recombinant protein

A 2.9 kDa recombinant-Fasciola hepatica protein (FhrAPS) was employed to estimate the prevalence of fasciolosis in sheep maintained under field conditions. For this purpose, 340 samples with known status in relation to fasciolosis by using a direct-ELISA and the coprological sedimentation were used. These samples were analysed by using an indirect-ELISA (iELISA) and the FhrAPS recombinant protein and excretory/secretory antigens (FhES) of this trematode. Current fasciolosis (CF) was named when results were positive to antigenemia and/or coprology. Out of 198 sheep with current fasciolosis, 68% were positive to the FhrAPS-ELISA test and 53% to the FhES. We observed 14% of the CF-neg sheep were positive to the FhrAPS, whereas this percentage was 52% with the FhES. A significant correlation between FhrAPS and current fasciolosis was obtained (r2=0.513, p=0.001). We concluded that the FhrAPS provides a more suitable antigen than FhES for developing field trials to know the prevalence of early and current fasciolosis.     

Antimicrobial susceptibility of Pasteurella multocida and Bordetella bronchiseptica from dogs and cats as determined in the BfT-GermVet monitoring program 2004-2006

A total of 92 canine/feline Pasteurella multocida strains form respiratory tract infections or infections of skin/ear/mouth as well as 42 canine/feline Bordetella bronchiseptica strains from respiratory tract infections were investigated for their susceptibility to antimicrobial agents. While the P. multocida strains were susceptible to all antimicrobial agents tested - except sulfonamides -, a considerable number of the B. bronchiseptica strains was resistant or exhibited high MIC values against a number of antimicrobial agents including penicillin G, oxacillin, cefazolin, ceftiofur, cefquinome, sulfamethoxazole, and trimethoprim/sulfamethoxazole.     

Pharmacokinetics of a single intravenous dose of marbofloxacin in adult donkeys

Six donkeys each received 2 mg/kg marbofloxacin as a 10 per cent aqueous solution administered intravenously. Principal pharmacokinetic parameters were determined and two efficacy indices were computed by using pharmacokinetic parameters and selected mic90 values of marbofloxacin against pathogenic equine strains to predict the efficacy of the drug at this dose. The pharmacokinetics of marbofloxacin in donkeys was characterised by a large mean volume of distribution at a steady state (1.15 [0.09] l/kg) and a long mean (sd) elimination half-life of 9.24 (1.96) hours. It was also characterised by a relatively slow total body clearance of 0.10 (0.02) l/kg/hour, slower than in horses. Using mic90 values of marbofloxacin against pathogenic equine strains with a daily dose of 2 mg/kg, appropriate values of efficacy indicators were obtained only for Enterobacteriaceae. Daily intravenous doses of 0.33, 2.62 and 20 mg/kg were calculated for evaluation in clinical trials of infections due to Enterobacteriaceae, Staphylococcus aureus and Streptococci, respectively.     

Influence of climatic and management factors on Eimeria infections in goats from semi-arid zones

A survey of Eimeria infections was performed in dairy goats and kids (<6 months old) of six farms from a dry desert area of Gran Canaria Island (Spain). The number of oocysts per gram of faeces (OPG) was determined by a modified McMaster technique over a total of 2,616 individual faecal samples taken from the rectum in monthly intervals. Eimeria oocysts were found in 96.1% of the samples with OPG ranging from 1 x 10(2) to 1.4 x 10(6). Kid goats had significantly (P < 0.001) higher OPG counts (46,496 +/- 5,228) than dairy females (2,225 +/- 287). Eight Eimeria species were identified, with Eimeria ninakohlyakimovae (30.0%), Eimeria arloingi (28.6%) and Eimeria alijevi (20.5%) being the most frequent species followed by Eimeria caprina (9.1%), Eimeria christenseni (4.5%), Eimeria jolchijevi (3.4%), Eimeria caprovina (3.2%) and Eimeria hirci (0.7%). Although significant differences were observed among goat groups and herds, the eight species were present in the six farms in both dairy goats and kids. The intensity of oocysts shedding was related to some factors such as the size of the herd and was further influenced by the prevailing climatic conditions of the area. The highest OPG counts were recorded during the hot season in dairy goats and close to weaning time in kids reared in small farms having no prophylactic treatments against eimeriosis.