Rubber tree (Hevea brasiliensis) trunk phloem necrosis: aetiological investigations failed to confirm any biotic causal agent

Trunk phloem necrosis (TPN) is currently a main constraint in rubber (Hevea brasiliensis) plantations. The apparent spread of the disease, from tree to tree along the planting line, strongly supported the implication of a pathogen that could be transmitted mechanically via the tapping knife. In order to detect a causal agent of the disease, studies focusing on characterization of the known mechanically transmitted pathogens (e.g. viroids, cryptic viruses or phytoplasma) were initiated. RNA strands of low molecular weight (200–400 and >500 bp) displaying structural similarities with viroids and viral dsRNAs were observed in various tested samples. However, attempts to show the potential role of these RNA molecules in the spread of the disease failed. First of all, there was no significant or reproducible correlation between the health status of the rubber trees sampled and these RNA molecules. Moreover, no sequence homology with known pathogens could be found when randomly amplified cDNA fragments isolated from trees presenting the disease symptoms were sequenced. In conclusion, the aetiological investigations, in order to show the presence of a pathogen responsible of the TPN disease, were non‐conclusive, which tends to disprove the hypothesis of a biotic causal agent.     

Phytoremediation and Modeling of Contaminated Soil using Eastern Gamagrass and Annual Ryegrass

The effectiveness of a warm season grass (eastern gamagrass), a cool season grass (annual ryegrass) and a rotation of warm and cool season grasses in the remediation of soil freshly contaminated with trinitrotoluene (TNT) and polybrominated biphenyls (PBBs) was evaluated. A total of 96 columns were filled with a Weswood silt loam soil that was mixed with TNT and PBB compounds to a target concentration of 10 mg of each contaminant. Chemical losses during this two-year field lysimeter experiment were similar for all experimental treatments and at all depths. Although higher microbial biomass was found in the rhizosphere soil, enumeration of soil microorganisms revealed a robust population in both the bulk and rhizosphere soils and the microbial growth was not dependent on root exudates only. Microbial degradation rates in the freshly contaminated soil were more affected by soil properties and the chemical characteristics of the contaminant than the presence of roots. The field data collected from the lysimeter experiment was used to calibrate a recently developed phytoremediation model. The phytoremediation computer model successfully simulated TNT soil concentrations in the column lysimeters. The model may be a valuable tool for the selection and optimization of phytoremediation methods at contaminated field sites.     

Global patterns of influenza a virus in wild birds

The outbreak of highly pathogenic avian influenza of the H5N1 subtype in Asia, which has subsequently spread to Russia, the Middle East, Europe, and Africa, has put increased focus on the role of wild birds in the persistence of influenza viruses. The ecology, epidemiology, genetics, and evolution of pathogens cannot be fully understood without taking into account the ecology of their hosts. Here, we review our current knowledge on global patterns of influenza virus infections in wild birds, discuss these patterns in the context of host ecology and in particular birds' behavior, and identify some important gaps in our current knowledge.