Phylogenetic and Morphological Identification of the Novel Pathogen of Rheum palmatum Leaf Spot in Gansu, China.

A new leaf spot disease was observed on leaves of Rheum palmatum (Chinese rhubarb) in Northwest China (Gansu Province) starting in 2005. A Septoria-like fungus was isolated and completion of Koch's postulates confirmed that the fungus was the casual agent of the leaf spot disease. Morphology and molecular methods were combined to identify the pathogen. The fungus produced conidiomata pycnidia and the conidia were 2~5 septate, 61.2~134.1 µm in length and 3.53~5.3 µm in width, which is much larger than the known Spetoria species that infects Polygonaceae species. Phylogenic analysis of the internal transcribed spacer region confirmed that this Spetoria-like fungus is within the Spetoria genus but distinct from known Spetoria species. Together, these morphological and phylogenetic data support that the R. palmatum infecting Spetoria strain is a newly-described plant pathogenic species.

Silver halide/silver iodide@silver composite with excellent visible light photocatalytic activity for methyl orange degradation.

AgBr/AgI@Ag composite photocatalyst was prepared by a handy multistep route, including controllable double-jet precipitation to synthesize cubic AgBr microcrystals, ion exchange to form AgI on AgBr surface, and visible light reduction to generate Ag nanoparticles. UV-Vis diffuse reflectance and electrochemical impedance spectra demonstrated that AgBr/AgI composite structure not only favors forming more silver nanoparticles to harvest visible light but also facilitates the transfer of charge carriers when compared with pure AgBr. Beneficial from the synergistic effect of highly effective visible light harvest and electron-hole separation, AgBr/AgI@Ag shows higher photocatalytic activity for the degradation of methyl orange (MO) than AgBr, AgBr@Ag, and AgBr/AgBr.