Replant problems in South Tyrol: role of fungal pathogens and microbial populations in conventional and organic apple orchards

South Tyrol, the main Italian apple growing area, is characterised by an highly intensive soil cultivation. Previous investigations shows the existence of replant disorders although it has not been evaluated which are the main causes. A survey has been carried out in this area with two main aims I) to evaluate the role of soil borne pathogens in apple replant disease and II) to evaluate the effect of soil management toward soil borne pathogens causing replant diseases. The experimental sites were chosen in order to obtain three couples of contiguous conventional and organic apple orchards. Soil sickness test with young apple plants gave a significant growth reduction in all soil samples if compared to a peat control. Among all root colonising fungi (Fusarium oxysporum, F. solani, Aphanomyces sp., Cy/incrocarpon sp., Rhizoctonia sp. and Pythium sp.) some Rhizoctonia solani strains and all Pythium spp. were the most pathogenic. In all cases organic management seems to reduce the soil sickness severity caused by root rot fungal pathogens

Ab initio calculations for bromine adlayers on the Ag(100) and Au(100) surfaces: the c(2x2) structure

Ab initio total-energy density-functional methods with supercell models have been employed to calculate the c(2x2) structure of the Br-adsorbed Ag(100) and Au(100) surfaces. The atomic geometries of the surfaces and the preferred bonding sites of the bromine have been determined. The bonding character of bromine with the substrates has also been studied by analyzing the electronic density of states and the charge transfer. The calculations show that while the four-fold hollow-site configuration is more stable than the two-fold bridge-site topology on the Ag(100) surface, bromine prefers the bridge site on the Au(100) surface. The one-fold on-top configuration is the least stable configuration on both surfaces. It is also observed that the second layer of the Ag substrate undergoes a small buckling as a consequence of the adsorption of Br. Our results provide a theoretical explanation for the experimental observations that the adsorption of bromine on the Ag(100) and Au(100) surfaces results in different bonding configurations.Comment: 10 pages, 4 figure, 5 tables, Phys. Rev. B, in pres

Growth and properties of strained VOx thin films with controlled stoichiometry

We have succeeded in growing epitaxial films of rocksalt VOx on MgO(001) substrates. The oxygen content as a function of oxygen flux was determined using 18O2-RBS and the vanadium valence using XAS. The upper and lower stoichiometry limits found are similar to the ones known for bulk material (0.8<x<1.3). From the RHEED oscillation period a large number of vacancies for both vanadium and oxygen were deduced, i.e. ~16% for stoichiometric VO. These numbers are, surprisingly, very similar to those for bulk material and consequently quite strain-insensitive. XAS measurements reveal that the vacancies give rise to strong low symmetry ligand fields to be present. The electrical conductivity of the films is much lower than the conductivity of bulk samples which we attribute to a decrease in the direct overlap between t2g orbitals in the coherently strained layers. The temperature dependence of the conductivity is consistent with a variable range hopping mechanism.Comment: 12 pages, 16 figures included, revised versio