Landscape ecology: a framework for integrating pattern and process in river corridors

Investigations of European floodplain rivers demonstrate how landscape ecology can provide an effective framework to integrate pattern and process in river corridors, to examine environmental dynamics and interactive pathways between landscape elements, and to develop viable strategies for river conservation. The highly complex and dynamic nature of intact river corridors is particularly amenable to a landscape ecology perspective. Analysis of spatial patterns has provided considerable insight into environmental heterogeneity across river corridors and is an essential prelude to examining dynamic interactions. For example, data from aerial photographs, digitized maps and year-round field measurements in a glacial flood plain, enabled us to distinguish six channel types, based on the correspondence between connectivity and physicochemical attributes. Spatial data were also used to analyze longitudinal changes in landscape elements along the course of a morphologically-intact riverine corridor, providing insight into the structural complexity that must have characterized many Alpine rivers in the pristine state. Landscape indices were employed to investigate seasonal dynamics in a glacial flood plain of the Swiss Alps which exhibits a predictable expansion/contraction cycle, with corresponding shifts in flow paths (surface and subsurface) and water sources (snowmelt, englacial, subglacial, alluvial aquifer, hillslope aquifer). Surface connectivity exhibited an unexpected biphasic relationship with total channel length, whereas riverscape diversity progressively increased along the entire range of channel length. Reconstituting the functional integrity that characterizes intact river corridors should perhaps be the major goal of river conservation initiatives. Although understanding functional processes at the landscape scale is essential in this regard, few data are available. In the Alluvial Zone National Park on the Austrian Danube, three phases of hydrological connectivity were identified (disconnection, seepage connection and surface connection) that corresponded to the predominance of three functional processes (biotic interactions, primary production and particulate transport) within the river corridor.     

Variation in the response of melon genotypes to Fusarium oxysporum f.sp. melonis race 1 determined by inoculation tests and molecular markers

Screening of genotypes of melon ( Cucumis melo ) for resistance to wilt caused by Fusarium oxysporum f.sp. melonis is often characterized by wide variability in their responses to inoculation, even under carefully controlled conditions. The variability at the seedling stage of 17 genotypes susceptible to race 1 was examined in growth-chamber experiments. Disease incidence varied from 0 to 100% in a genotype-dependent manner. Using four combinations of light (60 and 90  µ E m⁻² s⁻¹) and temperatures of (27 and 31°C), only light intensity showed a statistically significant effect. Marker-assisted selection for fusarium resistance breeding using cleaved amplified polymorphic sequence (CAPS) and sequence-characterized amplified region (SCAR) markers were compared using a single set of genotypes that included 24 melon accessions and breeding lines whose genotype regarding the Fom-2 gene was well characterized. The practical value of the markers for discriminating a range of genotypes and clarifying the scoring of phenotypes was also tested using a segregating breeding population which showed codominant SCAR markers to be useful in marker-assisted selection.     

Comparison of Crinipellis perniciosa isolates from Brazil by ERIC repetitive element sequence-based PCR genomic fingerprinting

Fifty isolates of Crinipellis perniciosa originating from Theobroma cacao , Heteropterys acutifolia and Solanum lycocarpum , from six states within Brazil, were characterized through ERIC-PCR, representing the first application of this method for molecular characterization within C. perniciosa . Phenetic analysis of banding patterns revealed a separation of isolates on the basis of host of origin, with T. cacao -derived isolates showing only a 0·2 similarity level to a cluster comprising the isolates from H. acutifolia and S. lycocarpum . Considerable intraspecific variability was observed within C. perniciosa isolates from T. cacao , with distinct groups observed correlating with geographical origin. Given that a number of isolates from T. cacao from the Amazon region grouped with isolates from Bahia state, this work discusses the possibility that current C. perniciosa populations pathogenic on T. cacao in Bahia originated from the Amazon region, rather than from alternative host plants.     

Resistance to Leveillula taurica in the genus Capsicum

One hundred and sixty-two Capsicum genotypes were evaluated for powdery mildew (Leveillula taurica) resistance, following inoculations with a suspension of 5 × 10⁴ conidia mL⁻¹ on 10-leaved to 12-leaved plants. Genotypes were graded into five resistance classes, based on the areas under the disease progress curves calculated from disease incidence (percentage infected leaves per plant) and severity (total number of colonies per plant). Results revealed a continuum from resistance to susceptibility, with the majority (70%) of C. annuum materials being classified as moderately to highly susceptible to L. taurica. Conversely, C. baccatum, C. chinense and C. frutescens were most often resistant, indicating that resistance to L. taurica among Capsicum species is found mainly outside the C. annuum taxon. Nevertheless, some resistant C. annuum material was identified that may be useful for resistance breeding. Eight genotypes were identified as immune to the pathogen: H-V-12 and 4638 (previously reported), and CNPH 36, 38, 50, 52, 279 and 288. Only H-V-12 and 4638 are C. annuum, while all others belong to the C. baccatum taxon. Latent period of disease on a set of commercial sweet pepper genotypes varied, indicating diverse levels of polygenic resistance. The latent period progressively reduced with plant maturity, from 14·3 days in plants at the mid-vegetative stage to 8·6 days in plants at the fruiting stage. Young plants of all commercial genotypes tested at the early vegetative stage were immune, irrespective of the reaction of the genotype at later stages, demonstrating widespread juvenile resistance to L. taurica in the Capsicum germplasm. Inoculation of plants of different botanical taxa with a local isolate indicated a wide host range. Some hosts, including tomato (Lycopersicon esculentum), artichoke (Cynara scolymus) and poinsettia (Euphorbia pulcherrima), produced large amounts of secondary inoculum. Other hosts included okra (Abelmoschus esculentus), eggplant (Solanum melongena), cucumber (Cucumis sativus), Solanum gilo, Chenopodium ambrosioides and Nicandra physaloides.     

A dynamic simulation model for powdery mildew epidemics on winter wheat*

A system dynamic model for epidemics of Blumeria graminis (powdery mildew) on wheat was elaborated, based on the interaction between stages of the disease cycle, weather conditions and host characteristics. The model simulates the progress of disease severity, expressed as a percentage of powdered leaf area, on individual leaves, with a time step of one day, as a result of two processes: the growth of fungal colonies already present on the leaves and the appearance of new colonies. By means of mathematical equations, air temperature, vapour pressure deficit, rainfall and wind are used to calculate incubation, latency and sporulation periods, the growth of pathogen colonies, infection and spore survival. Effects of host susceptibility to infection, and of leaf position within the plant canopy, are also included. Model validation was carried out by comparing model outputs with the dynamics of epidemics observed on winter wheat grown at several locations in northern Italy (1991–98). Simulations were performed using meteorological data measured in standard meteorological stations. As there was good agreement between model outputs and actual disease severity, the model can be considered a satisfactory simulator of the effect of environmental conditions on the progress of powdery mildew epidemics.     

A model estimating the risk of Fusarium head blight on wheat*

A dynamic simulation model for the risk of Fusarium head blight on wheat was elaborated based on systems analysis. The model calculates a daily infection risk based on sporulation, spore dispersal and infection of host tissue of the four main species causing the disease (Gibberella zeae, Fusarium culmorum, Gibberella avenacea, Monographella nivalis). Spore yield and dispersal are calculated as functions of temperature, rainfall and relative humidity, while the main factors affecting the infection rate are temperature, wetness and the host growth stage. The model also calculates a risk for mycotoxin production by G. zeae and F. culmorum in the infected head tissue. First validations against field data, collected in some wheat‐growing areas in northern Italy and not used in model elaboration, produced satisfactory results.     

Estimating the potential development of Diaporthe helianthi epidemics in Italy*

Diaporthe helianthi is the causal agent of a severe sunflower disease but, in Italy, disease outbreaks are sporadic with no significant losses. The present work investigates the role of meteorological conditions on the potential development of D. helianthi epidemics in Italy, using the French model Asphodel, which simulates the effect of air temperature, relative humidity and rainfall on ascospore maturation and dispersal, infection establishment, disease onset and severity during the period of host susceptibility. Meteorological data measured in eight stations distributed from north to south Italy, over a 5‐year period (1995–99), was used as model input. Results showed that meteorological conditions in Italy are frequently favourable for D. helianthi infections on sunflower, and severe epidemics are possible. Therefore, climatic conditions are not a limiting factor for disease development in the Italian sunflower‐growing areas. The lack of disease epidemics in Italy may be related to differences in the pathogen populations compared with the French ones.     

Production and characterization of a monoclonal antibody specific to the M serotype of plum pox potyvirus

A monoclonal antibody to an Albanian isolate of plum pox potyvirus (PPV) was obtained (MAbAL), that specifically recognized strain M of this virus. The specificity of MAbAL, assessed by comparative ELISA on 130 PPV isolates of different geographical origin, 22 of which were also tested by comparative IC-PCR, gave consistent and highly reproducible results. MAbAL seems to be elicited by a stable surface determinant that makes it particularly suitable for successful use under a wide range of conditions. MAbAL is an useful addition to the panel of PPV-specific MAbs available to date.