Mode of resistance to respiration inhibitors at the cytochrome bc1 enzyme complex of Mycosphaerella fijiensis field isolates

Field isolates of Mycosphaerella fijiensis, causing black Sigatoka of banana, were characterised for their sensitivity to different inhibitors of the cytochrome bc₁ enzyme complex (Qo respiration inhibitors, strobilurin fungicides), using physiological, biochemical and molecular genetic methods. Strobilurin‐resistant isolates exhibited very high resistance factors both in mycelial growth inhibition and NADH consumption assays. Cross‐resistance was observed among all Qo inhibitors, including trifloxystrobin, azoxystrobin, famoxadone, strobilurin B and myxothiazol. However, the Qi and the cytochrome aa₃ inhibitors, antimycin A and potassium cyanide, respectively, were not cross‐resistant to Qo inhibitors. In sensitive but not in resistant isolates, mixtures of Qo inhibitors and SHAM, an inhibitor of the alternative oxidase (AOX), were more active than the components alone, indicating that the alternative pathway is essential in metabolism, but not causal for resistance. In the cell‐free NADH‐consumption assay, the Qo inhibitors affected the sensitive but not the resistant isolates, suggesting that AOX was not active in sub‐mitochondrial particles. In whole cells, however, the AOX has a basic expression level and is probably not inducible by trifloxystrobin. Sequencing of the cytochrome b gene of sensitive and resistant M fijiensis isolates revealed a difference in the nucleotide sequence leading to a single amino acid change from glycine to alanine at position 143 in the resistant isolate. This change is known to occur also in the naturally tolerant basidiomycete Mycena galopoda. It is suggested that the field isolates of M fijiensis can acquire resistance to Qo inhibitors due to a target site alteration with a single base pair change. Resistant isolates do not seem to contain a mixture of mutated and non‐mutated DNA, indicating a complete selection of resistant mitochondria and a maternally donated mode of resistance. © 2000 Society of Chemical Industry     

Transmission by Olpidium brassicae of Mirafiori lettuce virus and Lettuce big-vein virus, and Their Roles in Lettuce Big-Vein Etiology

ABSTRACT Big-vein disease occurs on lettuce worldwide in temperate conditions; the causal agent has been presumed to be Lettuce big-vein virus (LBVV), genus Varicosavirus, vectored by the soilborne fungus Olpidium brassicae. Recently, the role of LBVV in the etiology of big-vein disease has been questioned because a second soilborne virus, Mirafiori lettuce virus (MiLV), genus Ophiovirus, has been found frequently in big-vein-affected lettuce. LBVV and MiLV, detectable and distinguishable by enzyme-linked immunosorbent assay using specific antisera, were tested for their ability to be transmitted from lettuce to lettuce by mechanical inoculation of sap extracts, or by zoospores of O. brassicae, and to cause big-vein disease. Both viruses were mechanically transmissible from lettuce to herbaceous hosts and to lettuce, but very erratically. LBVV was transmitted by O. brassicae but lettuce infected with only this virus never showed symptoms. MiLV was transmitted in the same manner, and lettuce infected with this virus alone consistently developed big-vein symptoms regardless of the presence or absence of LBVV. With repeated mechanical transmission, isolates of both viruses appeared to lose the ability to be vectored, and MiLV appeared to lose the ability to cause big-vein symptoms. The recovery of MiLV (Mendocino isolate, from Cali-fornia) from stored O. brassicae resting spores puts the earliest directly demonstrable existence of MiLV at 1990.     

Fragrance heritability in Hybrid Tea roses

Most of the Hybrid Tea roses that are sold as cut flowers are non-scented, despite the long-standing interest of the perfume industry to rose scent. In the absence of comprehensive knowledge on the genetic and biochemistry of volatile biosynthesis in roses, we decided to characterize a Hybrid Tea progeny obtained from parents that emit very different scents. First, we identified the 11 most abundant volatile compounds synthesized by the progeny, and a short review is given for each one that describes their occurrence in the genus Rosa, in the parents and the studied progeny. We have then used statistical analysis on the distribution of volatiles among individual progeny members to unveil the laws of segregation of the scent traits in this cross. As a general rule, the quantity and quality of volatile compounds was lower in the progeny members. Variations in scent quality were mostly linked to the quantity of monoterpenes that was present. Offsprings emitting a pleasant fragrance were, in practice, found to be rare.     

Landscape ecology of <Emphasis Type="Italic">Phragmites australis</Emphasis> invasion in networks of linear wetlands

The interaction between landscape structure and spatial patterns of plant invasion has been little addressed by ecologists despite the new insights it can provide. Because of their spatial configuration as highly connected networks, linear wetlands such as roadside or agricultural ditches, can serve as corridors facilitating invasion at the landscape scale, but species dynamics in these important habitats are not well known. We conducted a landscape scale analysis of Phragmites australis invasion patterns (1985–2002 and 1987–2002) in two periurban areas of southern Québec (Canada) focusing on the interaction between the network of linear wetlands and the adjacent land-uses. Results show that, at the beginning of the reference period, the two landscapes were relatively non-invaded and populations occurred mostly in roadside habitats which then served as invasion foci into other parts of the landscape. The intrinsic rates of increase of P. australis populations in linear anthropogenic habitats were generally higher than those reported for natural wetlands. Riparian habitats along streams and rivers were little invaded compared to anthropogenic linear wetlands, except when they intersected transportation rights-of-way. Bivariate spatial point pattern analysis of colonization events using both Euclidian and network distances generally showed spatial dependence (association) to source populations. An autologistic regression model that included landscape and edaphic variables selected transportation rights-of-way as the best predictor of P. australis occurrence patterns in one of the landscapes. Given the high invasion rates observed, managers of linear wetlands should carefully monitor expansion patterns especially when roads intersect landscapes of conservation or economic value.     

Cultural ecosystem services in an urban park: understanding bundles,trade-offs,and synergies

Landscape Ecology - Sets of ecosystem services that occur together across space or time are called ‘bundles’, and the interactions among them can result in synergies or trade-offs....     

Climate change will affect the ability of forest management to reduce gaps between current and presettlement forest composition in southeastern Canada

Landscape Ecology - Forest landscapes at the boreal–temperate ecotone have been extensively altered. Reducing the gap between current and presettlement forest conditions through...     

Rabies oral vaccination of foxes during the summer with the VRG vaccine bait

The vaccination of foxes by distributing vaccine baits in the environment was initiated in France in 1986. Two campaigns per year were carried out: one in the spring and one in the autumn. After the spring campaigns, only 22-52% of fox cubs consumed vaccine baits compared to 75% of the adults and 70-80% of the adults or fox cubs after autumn campaigns. In order to reduce the period of time during which fox cubs do not have access to baits and are not immunised, a vaccination campaign was organised during the summer of 1992 over a contaminated area of 25,748 km2 where vaccines had never previously been given. Vaccine bait stability was assessed during the same summer in the field and their appetence tested on captive foxes. The efficacy of the campaign was evaluated by the relative decrease in rabies incidence and the rate of bait uptake by foxes compared to those from neighbouring areas vaccinated for the first time with the same vaccine during the spring or autumn. Summer vaccination significantly increased (P < 0.01) bait uptake by fox cubs (71%) compared with spring vaccination (39%), but no significant difference was observed for adult foxes. Moreover, the decrease in rabies incidence, measured during the 6-month period following the campaigns was less pronounced after summer vaccination (49% decrease) than when the first vaccination was carried out during the spring or autumn (79 and 72% decrease, respectively). Three campaigns led to an apparent elimination of rabies when the first campaign was performed in the spring or autumn, but only to a 76% decrease in rabies incidence density index when the first campaign was performed during the summer. The high thermostability of the Raboral VRG bait permits its use during the summer for an emergency campaign. For routine vaccination plans, however, the classical calendar of spring and autumn vaccination campaigns should continue to be preferred.     

In situ imaging highlights local structural changes during heating: the case of meat

Understanding and monitoring deformation and water content changes in meat during cooking is of prime importance. We show the possibilities offered by nuclear magnetic resonance imaging (MRI) for the in situ dynamic measurement of deformation fields and water content mapping during beef heating from 20 to 75 °C. MRIs were acquired during heating, and image registration was used to calculate the deformation field. The temperature distribution in the sample was simulated numerically to link structural modifications and water transfer to temperature values. During heating, proton density decreases because of a magnetic susceptibility drop with temperature and water expulsion due to muscle contraction. A positive relationship was found between local cumulative deformation and water content. This new approach makes it possible to identify the deformation field and water transfer simultaneously and to trace thermal history to build heuristic models linking these parameters.