Powdery mildew of rubber tree caused by Oidium heveae is an important disease of rubber plantations worldwide. Identification and classification of this fungus is still uncertain because there is no authoritative report of its morphology and no record of its teleomorphic stage. In this study, we compared five specimens of the rubber powdery mildew fungus collected in Malaysia, Thailand, and Brazil based on morphological and molecular characteristics. Morphological results showed that the fungus on rubber tree belongs to Oidium subgen. Pseudoidium. Nucleotide sequence analysis of the ribosomal DNA internal transcribed spacer (ITS) region and the large subunit rRNA gene (28S rDNA) were conducted to determine the relationships of the rubber powdery mildew fungus and to link this anamorphic fungus with its allied teleomorph. The results showed that the rDNA sequences of the two specimens from Malaysia were identical to a specimen from Thailand, whereas they differed by three bases from the two Brazilian isolates: one nucleotide position in the ITS2 and two positions in the 28S sequences. The ITS sequences of the two Brazilian isolates were identical to sequences of Erysiphe sp. on Quercus phillyraeoides collected in Japan, although the 28S sequences differed at one base from sequences of this fungus. Phylogenetic trees of both rDNA regions constructed by the distance and parsimony methods showed that the rubber powdery mildew fungus grouped with Erysiphe sp. on Q. phillyraeoides with 100% bootstrap support. Comparisons of the anamorph of two isolates of Erysiphe sp. from Q. phillyraeoides with the rubber mildew did not reveal any obvious differences between the two powdery mildew taxa, which suggests that O. heveae may be an anamorph of Erysiphe sp. on Q. phillyraeoides. Cross-inoculation tests are required to substantiate this conclusion.

Pathogenicity tests were carried out on oil palm seedlings and germinated seeds using monokaryotic and dikaryotic mycelia in order to investigate the indirect role of basidiospores in initiating basal stem rot disease in oil palm. The pathogenicity tests conducted showed that monokaryotic mycelia were not able to cause infection while reconstituted dikaryotic mycelia could initiate basal stem rot infection on both oil palm seedlings and germinated seeds. The severity of the disease symptoms on both seedlings and germinated seeds was found to be related to the size of the inoculum, with larger inoculum resulting in more severe symptoms. The present study indicates that monokaryotic mycelia which originated from germinating basidiospores could colonise any available substrate and that basidiospores therefore indirectly played a role in basal stem rot infection in oil palm fields.

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ZnO(0001) surfaces probed by scanning tunneling spectroscopy: Evidence for an inhomogeneous electronic structure Appl. Phys. Lett. 95, 132102 (2009);The surface properties of ZnO nanobelts grown by chemical vapor deposition were investigated by tapping mode atomic force microscopy ͑AFM͒ and scanning tunneling microscopy ͑STM͒. AFM images showed a type 1 ͑high aspect ratio͒ nanobelt lying across a type 2 ͑low aspect ratio͒ nanobelt, bending at an angle of 20.9°without breaking.Step defects were also observed on the surface for the first time, with step edges running along the ͓−1 − 120͔ direction. These surface defects are also observed by STM while scanning tunneling spectroscopy measurements yield a band gap of 3.3 eV and near flatband conditions.

We present an AFM and STM-STS investigation of the surface of ZnO nanobelts grown by chemical vapour deposition. AFM images showed a type 1 (high aspect ratio) nanobelt lying across a type 2 (low aspect ratio) nanobelt, bending at an angle of 20.9 • without breaking. Terraces 10 atomic layer thick were also observed, with step edges running along the [0010] direction. STM images confirmed the AFM results while STS curves and current maps showed higher conductivity for the ZnO nanobelts than for the oxidised silicon surface, as well as an n-type behaviour.