Characterization of Phytophthora infestans isolates collected from potato in Flanders, Belgium

A collection of 49 isolates of Phytophthora infestans, collected from blighted potato foliage in 1998 in Flanders, were analysed for mating type, response to metalaxyl (48 isolates), allozymes of glucose-6-phosphate isomerase (Gpi), peptidase ( Pep) and restriction fragment length polymorphism ( RFLP) with probe RG57 (39 isolates). Forty-one A1 and eight A2 isolates were detected. Resistance to metalaxyl was frequently observed: 30 resistant, four intermediate and 14 sensitive isolates were found. Gpi genotypes 100/100 and 90/100 occurred in 30 and nine isolates, respectively. The dominating banding pattern for Pep was 100/100 (32 isolates), but genotypes 96/96, 96/100 and 83/96, never previously reported in continental western Europe, were also identified. Thirteen RG57 fingerprint were observed. On the basis of combined traits, 15 multilocus genotypes were revealed among 39 isolates. Genotypic diversity measured by the normalized Shannon diversity index was 0.56. The results indicate that, besides asexual variation and/or migration, sexual events may have played a role in the establishment of the isolates studied

Estimate of bottom and surface stress during a spring-neap tide cycle by dynamical assimilation of tide gauge observations in the Chesapeake Bay

Dynamical assimilation of surface elevation from tide gauges is investigated to estimate the bottom drag coefficient and surface stress as a first step in improving modeled tidal and wind-driven circulation in the Chesapeake Bay. A two-dimensional shallow water model and an adjoint variational method with a limited memory quasi-Newton optimization algorithm are used to achieve this goal. Assimilation of tide gauge observations from 10 permanent stations in the Bay and use of a two-dimensional model adequately estimate the bottom drag coefficient, wind stress, and surface elevation at the Bay mouth. Subsequent use of these estimates in the circulation model considerably improves the modeled surface elevation in the entire Bay. Assimilation of predicted tidal elevations yields a drag coefficient, defined in the hydraulic way, varying between 2.5 x 10(-4) and 3.1 x 10(-3) The bottom drag coefficient displays a periodicity corresponding to the spring-neap tide cycle with a maximum value during neap tide and a minimum value during spring tide. From assimilation of actual tide gauge observations, it is found that the fortnightly modulation is altered during frontal passage. Furthermore, the response of the sea surface to the wind forcing is found to be more important in the lower Bay than in the upper Bay, where the barometric pressure effect seems to be more important

A size-based ecosystem model for pelagic waters

10.1016/S0304-3800(98)00126-4Ecological Modelling112153-72ECMO