A unique species in Phytophthora clade 10, Phytophthora intercalaris sp. nov., recovered from stream and irrigation water in the eastern USA.

A novel species of the genus Phytophthora was recovered during surveys of stream and nursery irrigation water in Maryland, Massachusetts, North Carolina, Virginia and West Virginia in the USA. The novel species is heterothallic, and all examined isolates were A1 mating type. It produced rare ornamented oogonia and amphigynous antheridia when paired with A2 mating type testers of Phytophthora cinnamomi and Phytophthora cryptogea. Sporangia of this novel species were non-papillate and non-caducous. Thin-walled intercalary chlamydospores were abundant in hemp seed agar and carrot agar, while they were produced only rarely in aged cultures grown in clarified V8 juice agar. Phylogenetic analyses based on sequences of the internal transcribed spacer region and the ß-tubulin and mitochondrial cytochrome-c oxidase 1 (cox1) genes indicated that the novel species is phylogenetically close to Phytophthora gallica in Phytophthora clade 10. The novel species has morphological and molecular features that are distinct from those of other species in Phytophthora clade 10. It is formally described here as Phytophthora intercalaris sp. nov. Description of this unique clade-10 species is important for understanding the phylogeny and evolution of Phytophthora clade 10.

Temporal trends and sources of variation in carbon flux from coarse woody debris in experimental forest canopy openings.

Pulses of respiration from coarse woody debris (CWD) have been observed immediately following canopy disturbances, but it is unclear how long these pulses are sustained. Several factors are known to influence carbon flux rates from CWD, but few studies have evaluated more than temperature and moisture. We experimentally manipulated forest structure in a second-growth northern hardwood forest and measured CO2 flux periodically for seven growing seasons following gap creation. We present an analysis of which factors, including the composition of the wood-decay fungal community influence CO2 flux. CO2 flux from CWD was strongly and positively related to wood temperature and varied significantly between substrate types (logs vs. stumps). For five growing seasons after treatment, the CO2 flux of stumps reached rates up to seven times higher than that of logs. CO2 flux of logs did not differ significantly between canopy-gap and closed-canopy conditions in the fourth through seventh post-treatment growing seasons. By the seventh season, the seasonal carbon flux of both logs and stumps had decreased significantly from prior years. Linear mixed models indicated the variation in the wood inhabiting fungal community composition explained a significant portion of variability in the CO2 flux along with measures of substrate conditions. CO2 flux rates were inversely related to fungal diversity, with logs hosting more species but emitting less CO2 than stumps. Overall, our results suggest that the current treatment of CWD in dynamic forest carbon models may be oversimplified, thereby hampering our ability to predict realistic carbon fluxes associated with wood decomposition.

First Report of Downy Mildew Caused by a Peronospora Species on Sweet Basil (Ocimum basilicum) in Massachusetts.

In September of 2008, downy mildew was discovered to be causing a serious foliar blight of sweet basil at several farms and greenhouses in Massachusetts. Infected leaves had chlorotic vein-bounded patches and diffuse chlorosis, and a characteristic gray, fuzzy growth was on the abaxial surface. Microscopic observations revealed branched sporangiophores that measured 187.5 to 325 µm (average 285 µm) long. Sporangia measured 22.5 to 30 × 20 to 22.5 µm (average 26.7 × 20.9 µm). No oospores were found. Sporangium measurements are comparable to unnamed Peronospora species reported previously on basil from Italy, Switzerland, and South Africa (1,2). Sequence analyses were conducted on five isolates of 'Nufar' basil by extracting DNA from a sporangial suspension washed from leaves and infected leaf tissues using the Qiagen DNeasy plant tissue kit (Qiagen, Valencia, CA). PCR amplification of the ITS1, 5.8S, and ITS2 region was performed using primers ITS6 and ITS4 (3). The sequences of the five isolates were identical. BLAST analyses of the sequences revealed a 99% similarity to the unnamed Peronospora species on sweet basil in Europe and South Africa (1,2). To our knowledge, this is the first report of a Peronospora species on sweet basil in Massachusetts. References: (1) L. Belbahri et al. Mycol. Res. 109:1276, 2005. (2) A. McLeod et al. Plant Dis. 90:1115, 2006. (3) T. J. White et al. PCR Protocols: A Guide to Methods and Applications. M. A. Innis et al., eds. Academic Press, San Diego, 1990.