Putative new species of the genus Dickeya as major soft rot pathogens in Phalaenopsis orchid production

Bacterial soft rots are a serious limitation to the production of orchids and other horticultural plants. Here, the characterization of causative bacteria isolated from Phalaenopsis orchids showing symptoms, from a commercial production site, is reported. The most commonly isolated bacteria were identified as Dickeya spp. Partial sequencing of 16S rDNA, fliC and dnaX showed diversity among the isolates and divided the isolates into two groups, with greatest similarity to previously reported undefined Dickeya lineages from orchids (UDL‐3 and UDL‐4). Two isolates (B16, S1) were sequenced using next‐generation sequencing, which has provided draft genomes of these two isolates for further studies (Ali? et al., 2015 ). Newly developed fliC‐based lineage‐specific quantitative real‐time PCR assays were used to distinguish among the lineages and to assess their relative abundances in diseased tissues. Virulence and aggressiveness comparison tests in vivo on Phalaenopsis orchids, potato plants and witloof chicory leaves indicated high virulence and extreme maceration potential of these novel Dickeya isolates, compared to a reference panel of other Dickeya spp. Pantoea cypripedii (formerly Pectobacterium cypripedii), which has previously been reported as a soft rot pathogen of orchids, was not detected, and isolates obtained from culture collections did not cause symptoms on artificially infected Phalaenopsis orchids.     

Effects of long‐term grazing management on dandelion (Taraxacum officinale) in Agrostis capillaris grassland

Dandelion (Taraxacum officinale agg.) is a common forb species in grasslands in Europe. Although sometimes regarded as a valuable forage herb, it may become a weed, especially in arable land. There is limited information on the response of Taraxacum to long‐term grassland management practices. Therefore, we analysed cover and dry‐matter standing biomass of Taraxacum in a long‐term (1998–2012) grazing experiment on an Agrostis capillaris grassland. The following treatments were laid out on formerly abandoned grassland: (i) intensive grazing (IG); (ii) extensive grazing (EG); (iii) first cut followed by intensive grazing (ICG); (iv) first cut followed by extensive grazing (ECG); and (v) unmanaged grassland (U). During the first 10 years, all defoliation treatments (i–iv) supported the presence of Taraxacum, and the lowest proportion was recorded in the unmanaged treatment (U). During the final 7 years of the study, combined cutting and grazing promoted Taraxacum cover more than that of grazing only (ICG > IG > ECG > EG). Cover of Taraxacum was negatively affected by increasing sward height where Taraxacum plants had lower fitness. Due to the relatively strong relationship between percentage cover of Taraxacum and its dry‐matter biomass, percentage cover could be used as a simple method for the assessment of biomass of Taraxacum in a sward. Results are discussed in the context of adapting the management of A. capillaris grassland as a simple method for control of Taraxacum abundance, particularly in situations of extensification or abandonment.