RESUMEN
We develop a ReaxFF reactive force field used for the molecular dynamics simulations of thermophysical properties of liquid Cu and Zr metals. The ReaxFF parameters are optimized by fitting to the first-principles density-functional calculations on the equations of state for bulk crystal structures and surface energies. To validate the force field, we compare the ReaxFF results with those from experiments and embedded-atom-method (EAM) potentials. We demonstrate that the present ReaxFF force field well represents structural characteristics and diffusion behaviors of elemental Cu and Zr up to high-temperature liquid regions. It reasonably reproduces the thermodynamic processes associated with crystal-liquid interface. In particular, the equilibrium melting temperatures show better agreement with experimental measurements than the results from EAM potentials. The ReaxFF reactive force field method exhibits a good transferability to the nonreactive processes of liquid systems.
RESUMEN
Rhizoma paridis is a perennial, traditional Chinese medicinal herb. In May 2013, a disease was observed in an approximately 10 ha cultivated field in Enshi, Hubei Province, China. Approximately 80% of plants in the field were affected. Symptoms were visible on the basal leaves of affected plants. Chlorosis followed by necrosis started at the leaf tips and margins and gradually spread inward until the entire leaf was necrotic. Thick, gray mycelium and conidia were visible on both sides surface of leaves under wet, humid conditions. The leading edge of the chlorotic leaves was excised from 20 plant samples surface disinfested with 1% NaOCl solution for 1 min, rinsed in sterile water, air dried, and placed on potato dextrose agar (PDA). Plates were incubated at 22°C in the dark. Mycelia were initially hyaline and white, and became dark gray after 72 h. Mycelia were septate with dark branched conidiophores. Conidia were smooth, hyaline, ovoid, aseptate, and ranged from 8 to 14.5 × 7 to 8.5 µm. Numerous hard, small, irregular, and black sclerotia that were 1 to 3 × 2 to 5 mm were visible on PDA plates after 12 days. The fungus was identified as Botrytis cinerea on the basis of these characters (1). The internal transcribed spacer (ITS) region of rDNA was amplified using the ITS1 and ITS4 primer and sequenced (GenBank Accession No. KF265499). BLAST analysis of the PCR product showed 99% identity to Botryotinia fuckeliana (perfect stage of B. cinerea) (EF207415.1, EF207414.1). The pathogen was further identified to the species level as B. cinerea using gene sequences from glyceraldehyde-3-phosphate dehydrogenase (G3PDH), heat-shock protein 60 (HSP60), and DNA-dependent RNA polymerase subunit II (RPB2) (2) (KJ638600, KJ638602, and KJ638601). Pathogenicity was tested by spraying the foliage of 40 two-year-old plants with a suspension of 106 conidia per ml of sterile distilled water. Each plant received 30 ml of the inoculum. Ten healthy potted plants were inoculated with sterilized water as control. All plants were covered with plastic bags for 5 days after inoculation to maintain high relative humidity and were placed in a growth chamber at 22°C. The first foliar lesions developed on leaves 7 days after inoculation and were similar to those observed in the field. No symptoms developed on the control plants. B. cinerea was consistently re-isolated from all artificially inoculated plants. The pathogenicity test was completed twice. To our knowledge, this is the first report of gray mold of R. paridis caused by B. cinerea in China. The root of R. paridis is the most commonly used Chinese herbal medicine to treat viper bites. In recent years, cultivation of this herb has increased in China because of its high value. Consequently, the economic importance of this disease is likely to increase with the greater prevalence of this host species. References: (1) H. L. Barnett and B. B. Hunter. Illustrated Genera of Imperfect Fungi. Burgess Publishing Company, Minneapolis, MN, 1972. (2) M. Staats et al. Mol. Biol. Evol. 22:333, 2005.
