Epidemiology of Xiphinema americanum and Tomato ringspot virus on Red Raspberry, Rubus idaeus.

Population dynamics of Xiphinema americanum and transmission of Tomato ringspot virus (ToRSV) were studied in a red raspberry field in Washington State. Population densities of X. americanum were highest in the winter, lowest in the summer, and were correlated with precipitation (R2 = 0.42). All nematode stages were present throughout the year. Gravid females were observed only in the spring, indicating one generation per year. The sequence of the coat protein of the ToRSV from this field was similar to those of other raspberry isolates from the Pacific Northwest. Cucumber seedlings were planted in soil collected monthly from the field and were evaluated for nematode transmission of ToRSV by enzyme-linked immunosorbent assay (ELISA). The proportion of assay plants infected with ToRSV was negatively correlated with nematode densities (R2 = 0.31). In another study, ToRSV was detected by ELISA in fine roots of raspberry plants 5 months after planting in field soil infested with viruliferous nematodes, in all subterranean portions of plants after 12 months, and in all aerial portions the second year. The rate of spread of ToRSV in a raspberry field was 70 cm per year. These results suggest that the rate of ToRSV spread is limited by systemic spread of virus in plants when nematode-infested soil is not transported in the field.

Effects of Mesocriconema xenoplax on Vitis vinifera and Associated Mycorrhizal Fungi.

Previous surveys of vineyards had indicated that Mesocriconema xenoplax was present in 85% of vineyards in western Oregon, but yields were not depressed in established vines. Microplot studies were initiated in 1997 in a Willamette Valley vineyard to determine the impact of M. xenoplax on vine establishment. Plots were infested with 0.03, 0.6, and 3.0 M. xenoplax g(-1) soil and planted with self-rooted Chardonnay and Pinot Noir vines. In November 2000, four growing seasons after planting, pruning weights, fine root weights, and fruit yield of vines planted in infested soil were reduced by 58%, 75%, and 33%, respectively, relative to control vines (planted in noninfested soil). In 1998 with ca 2000 degree-day base 9 degrees C accumulation, population densities increased 32-fold and 44-fold on 1-year-old Chardonnay and Pinot Noir vines, respectively. Nematode population dynamics and pruning data suggested that the carrying capacity of vines in microplots was 5 to 8 M. xenoplax g(-1) soil. In November 2000, more than 80% of the fine root length was colonized by arbuscular mycorrhizal fungi in all treatments. The frequency of fine roots containing arbuscules (the site of nutrient transfer between plant and fungus), however, was depressed from 5% to 65% in plants infested initially with M. xenoplax as compared to controls. Competition for photosynthate within the root system is proposed as a possible mechanism by which nematodes suppressed arbuscule frequency.

The rfb genes in Azotobacter vinelandii are arranged in a rfbFGC gene cluster: a significant deviation to the arrangement of the rfb genes in Enterobacteriaceae.

We report the identification of rfbF and rfbC located adjacent to the previously identified rfbG (Gavini et. al. Biochem. Biophys. Res. Commun. 1997, 240, 153-161) from the non-symbiotic, non-pathogenic soil bacterium Azotobacter vinelandii. The rfbF open reading frame encodes a putative polypeptide of 256 amino acids. This polypeptide shares a homology of 74% with the RfbF of Synechocystis sp. and a 70% homology with the AscA of Yersinia pseudotuberculosis which function as alpha-D-glucose-1-phosphate cytidylyltransferases in the biosynthesis of the O-antigen. The rfbC encodes a putative polypeptide of 186 amino acids. It shows strongest homology to the RfbC of Synechocystis sp. (64%) and Salmonella typhimurium (40%). RfbC functions as a dTDP-4-Dehydrorhamnose 3,5-Epimerase. The genes identified here have a low G + C content (approximately 56%) as compared to the A. vinelandii chromosome (approximately 63%) which is characteristic of the rfb clusters identified in other bacteria and may be indicative of the acquisition of the rfb genes by interspecific gene transfer. Despite the high level of sequence conservation, the organization of the rfb genes in A. vinelandii deviates from the arrangement of the most thoroughly studied rfb gene clusters of Enterobacteriaceae.

Identification and mutational analysis of rfbG, the gene encoding CDP-D-glucose-4,6-dehydratase, isolated from free living soil bacterium Azotobacter vinelandii.

We have identified the rfbG from a non-symbiotic and non-pathogenic soil bacterium, Azotobacter vinelandii. The nucleotide sequence analysis of the rfbG revealed an open reading frame that encodes a peptide of 360 amino acids. This deduced peptide shares 57% homology with the RfbG of Synechocystis and 47% homology with the RfbG of Yersinia pseudotuberculosis. The previously identified short-chain dehydrogenases/reductases family signature sequence is conserved in the sequence of the RfbG of A. vinelandii. Southern blotting analysis of A. vinelandii chromosome by probed with 1.1 kb PstI DNA fragment corresponding to rfbG revealed that it is present as single copy on A. vinelandii chromosome. Disrupting the rfbG present on the chromosome of A. vinelandii, by insertion of kanamycin resistance marker via homologous recombination, resulted in drastic changes in the growth characteristics. The rfbG-negative A. vinelandii grown in liquid medium exhibited agglutination that is characteristic of rfb- mutants of other bacteria, suggesting that we have cloned the functional copy of the rfbG of A. vinelandii.

Stimulation of vesicular-arbuscular mycorrhizal fungi by mycotrophic and nonmycotrophic plant root systems.

Transformed root cultures of three nonmycotrophic and one mycotrophic plant species stimulated germination and hyphal growth of the vesicular-arbuscular mycorrhizal fungus Glomus etunicatum (Becker & Gerd.) in a gel medium. However, only roots of the mycotrophic species (carrot) supported continued hyphal exploration after 3 to 4 weeks and promoted appressoria formation by G. etunicatum.

Oxidation of Thianthrene by the Ligninase of Phanerochaete chrysosporium.

The oxidation of heterocyclic sulfur compounds reported to be part of the macrostructure of coal and petroleum was investigated. The oxidation of thianthrene solubilized in 10% dimethylformamide to thianthrene monosulfoxide in the presence of hydrogen peroxide was catalyzed by the ligninase from Phanerochaete chrysosporium.