Salicylic acid in Populus tomentosa is a remote signalling molecule induced by Botryosphaeria dothidea infection.

The salicylic acid (SA) plays a critical role during the establishment of systemic acquired resistance (SAR) in uninfected plant tissues after localised exposure to a pathogen. Here, we studied SA in Populus tomentosa infected by the plant pathogen Botryosphaeria dothidea. The accumulation of SA and methyl salicylate (MeSA) occurred in chronological order in P. tomentosa. The SA and MeSA contents were greater at infected than uninfected sites. Additionally, a gene expression analysis indicated that SA might be accumulated by phenylalanine ammonialyase (PAL) and converted to MeSA by SA carboxyl methyltransferase (SAMT), while MeSA might convert to SA by SA-binding protein 2 (SABP2). The expressions of SAMT at infected sites and SABP2 at uninfected sites, respectively, were significantly up-regulated. Thus, SA might be converted to MeSA at infected sites and transported as a signalling molecule to uninfected sites, where it is converted to SA for SAR. Moreover, the expressions of pathogenesis-related genes PR-1, PR-2 and PR-5 in P. tomentosa were up-regulated by the B. dothidea infection. Our study determined that variations in SA and MeSA contents occur at infected and uninfected sites in poplar after pathogen infection and contributed to the remote signals for poplar SAR.

Cytospora species from Populus and Salix in China with C. davidiana sp. nov.

Poplar and willow plantations have become widespread in China, in order to meet national economic and environmental needs. The emergence of several pathogens is enhanced by climatic change and associated human factors. Species of Cytospora are well-known pathogens on poplar and willow, and cause stem cankers and diebacks. In the present study, we conducted a survey of Cytospora species occurring on Populus spp. and Salix spp. in China. We used morphological examination and phylogenetic inferences, based on the DNA sequence data from the internal transcribed spacer regions (ITS1, 5.8S rDNA, and ITS2) and partial ß-tubulin gene, to identify six Cytospora species occurring on poplar and willow. Five of these species belonged to known taxa, viz. Cytospora chrysosperma (asexual state of Valsa sordida), Cytospora translucens (asexual state of Leucostoma translucens), Cytospora fugax (asexual state of Valsa salicina), Cytospora atrocirrhata, and Cytospora kantschavelii. Our study yielded a new species, Cytospora davidiana sp. nov., on poplar. The new species is characterized by typical torsellioid conidiomata. An additional Cytospora sp. 1, which formed a distinct clade in the phylogenetic inferences, remains unnamed; the paucity of available materials prevented phenotypical characterization.

Characterization of the Pinus massoniana transcriptional response to Bursaphelenchus xylophilus infection using suppression subtractive hybridization.

Pine wilt disease (PWD) caused by pine wood nematode (PWN), Bursaphelenchus xylophilus, is the most destructive diseases of pine and poses a threat of serious economic losses worldwide. Although several of the mechanisms involved in disease progression have been discovered, the molecular response of Pinus massoniana to PWN infection has not been explored. We constructed four subtractive suppression hybridization cDNA libraries by taking time-course samples from PWN-inoculated Masson pine trees. One-hundred forty-four significantly differentially expressed sequence tags (ESTs) were identified, and 124 high-quality sequences with transcriptional features were selected for gene ontology (GO) and individual gene analyses. There were marked differences in the types of transcripts, as well as in the timing and levels of transcript expression in the pine trees following PWN inoculation. Genes involved in signal transduction, transcription and translation and secondary metabolism were highly expressed after 24 h and 72 h, while stress response genes were highly expressed only after 72 h. Certain transcripts responding to PWN infection were discriminative; pathogenesis and cell wall-related genes were more abundant, while detoxification or redox process-related genes were less abundant. This study provides new insights into the molecular mechanisms that control the biochemical and physiological responses of pine trees to PWN infection, particularly during the initial stage of infection.

Micoletzkya chinaae n. sp. (Nematoda: Diplogastridae), a potential predacious nematode and Ektaphelenchus macrobulbosus (Nematoda: Ektaphelenchinae) isolated from Simao pine in South-western China.

Detailed morphology of a new diplogastrid and a known ektaphelenchid species isolated from Simao pine in south-western China were illustrated and described/redescribed. Micoletzkya chinaae n. sp. is characterized by a relatively short body length (601-802 µm in female and 505-773 µm in male), undivided cheilorhabdia (forming an entire ring), dimorphic buccal cavity (eury- or stenostomatous), a large claw-like dorsal tooth and a large right subventral tooth in the stoma of eurystomatous form, typical diplogastrid pharynx, didelphic female gonads, nine pairs of genital papillae on male tail region with two ventral pairs (GP1 and GP2) closely associated, a unique gubernaculum morphology, and a long filiform tail in both sexes. The new diplogastrid belongs to the Group 1 category of Micoletzkya species sensuMassey, 1966, which is characterized by stoma equipped with a large dorsal and a large subventral tooth, and both teeth can cross near the center of the pharynx. The new species can be easily distinguished from other species within this group except for M. tomeaMassey, 1966 with the long filiform female and male tails. However, it shows great similarities to Mononchoides spp., Koerneria spp., Fictor spp., and Acrostichus members in some aspects. More morphological features as well as molecular data of this clade should be available before relationships between and within these genera can be better interpreted. The two large moveable teeth in eurystomatous worms indicate their potentially predacious habits, and re-isolation of this species is necessary. Morphology of south-western Chinese population of Ektaphelenchus macrobulbosus (Rühm,1956) Massey, 1974 conforms well to the previous descriptions except for a few minor variations. It is characterized by medium-long female and male bodies (676-791 and 613-685 µm, respectively), three incisures in the lateral field, offset cephalic region, knobless stylet 18-20 µm long, oblong median bulb with posteriorly situated valves, two to three rows of developing oocytes, short postuterine sac, absence of female rectum and anus, two pairs of subventral papillae on the male tail region, a cucullus (apophysis) present on the dorsal distal end of the spicule, and the conoid female and male tails.

Ophiostomatoid fungi (Ascomycota) associated with Pinus tabuliformis infested by Dendroctonus valens (Coleoptera) in northern China and an assessment of their pathogenicity on mature trees.

Dendroctonus valens is an invasive pest in coniferous forests of northern China. It was suspected of being responsible for the death of more than three million Pinus tabuliformis trees. The present study sought to identify the ophiostomatoid fungi associated with D. valens in northern China and understand the possible role of these fungi in the pine decline. On the basis of morphology, physiology, mating compatibility and phylogenetic analyses of multiple DNA sequences, seven species of ophiostomatoid fungi were isolated from and around D. valens galleries: Leptographium alethinum, Grosmannia koreana (teleomorph of L. koreanum), L. procerum, L. sinoprocerum, L. truncatum, Pesotum aureum and P. pini. All have been recorded for the first time in China. Among them, the occurrence of the dominant species L. procerum is positively linked to attack intensities of D. valens. The pathogenicity of four species (L. koreanum, L. procerum, L. sinoprocerum and L. truncatum) was tested on mature P. tabuliformis trees by stem inoculation. All inoculated strains caused significant necrotic lesions on the inner bark. However, L. koreanum and L. truncatum induced more extensive lesions than L. procerum and L. sinoprocerum. Their association with D. valens and the P. tabuliformis decline is discussed.

Leptographium sinoprocerum sp. nov., an undescribed species associated with Pinus tabuliformis-Dendroctonus valens in northern China.

During a study of ophiostomatoid fungi associated with the invasive pest Dendroctonus valens in the Pinus tabuliformis ecosystem in northern China, a multigenic (ITS2-LSU, beta-tubulin and EF1-alpha) phylogenetic analysis and examination of morphological features revealed in addition to Leptographium procerum the occurrence of an undescribed species. The new species, Leptographium sinoprocerum, belongs to the L. procerum-L. profanum clade. Both L. procerum and L. sinoprocerum are similar to each other and occur sympatrically in the ecosystem studied. Nevertheless L. sinoprocerum can be distinguished from L. procerum by shorter conidiophore stipes arising from both submerged and aerial hyphae, slightly more oblong conidia, a granular ornamentation on the submerged hyphae and dark olivaceous colonies on MEA.