STUDIES ON THE BACTERIAL DIE-BACK AND CANKER DISEASE OF POPLAR

Artificial freezing caused leaf necrosis and twig die-back but did not produce cracks or cankers on living branches of three varieties of poplar. Freezing increased the damage caused by a well-established infection of the bacterial die-back and canker but checked new lesions. Freezing prior to infection has no appreciable effect on the establishment of the disease.     

辽北地区农田防护林杨树新无性系的引进与优选

在辽宁省昌图县前双井镇以引进的6个无性系新品种杨树为材料,用乡土杨富杂Ⅱ号为对照作栽培比较试验,观察其生长量,抗寒性,感病性,感虫性等指标,用评分法评价各种综合表现的优劣。结果表明,N－119杨各项指标明显地超过对照,并优于其它品种,可扩大栽培,赛路杨生长量明显地超过本地乡土杨,且感病性,抗寒性等方面等于或接近对照,有一定的引种价值。     

杨属（PopulusL.）种质资源遗传学评价研究进展

杨属（PopulusL.）种质资源极其丰富,为了有效保存、合理利用杨属种质资源,国内外开展了大量的种质资源遗传学评价研究。该文在介绍杨树系统分类的基础上,概述了白杨派、青杨派和黑杨派等在生物学特性、抗性（耐盐、抗旱、抗冻及抗病虫）、适应性及DNA遗传多态性等方面的遗传学评价研究进展,重点讨论了杨树种质资源评价研究中存在的问题和不足,并对其研究前景进行了展望。     

杨属(Populus L.)种质资源遗传学评价研究进展

杨属(Populus L.)种质资源极其丰富, 为了有效保存、合理利用杨属种质资源, 国内外开展了大量的种质资源遗传学评价研究。该文在介绍杨树系统分类的基础上, 概述了白杨派、青杨派和黑杨派等在生物学特性、抗性(耐盐、抗旱、抗冻及抗病虫)、适应性及DNA遗传多态性等方面的遗传学评价研究进展, 重点讨论了杨树种质资源评价研究中存在的问题和不足, 并对其研究前景进行了展望。     

CD4+CD25+ suppressor T cells regulate pathogen induced inflammation and disease

A key suppressor role has recently been ascribed to the natural CD4+CD25+ regulatory T cells (Treg), the removal of which leads to the development of autoimmune disease and aggravated pathogen-induced inflammation in otherwise normal hosts. The repertoire of antigen specificities of Treg is as broad as that of naive T cells, recognizing both self and non-self antigens, enabling Treg to control a broad range of immune responses. Although widely acknowledged to play a role in the maintenance of self-tolerance, recent studies indicate that Treg can be activated and expanded against bacterial, viral and parasite antigens in vivo. Such pathogen-specific Treg can prevent infection-induced immunopathology but may also increase the load of infection and prolong pathogen persistence by suppressing protective immune responses. This review discusses the role of Treg in the prevention of exaggerated inflammation favoring chronicity in bacterial or fungal infections and latency in viral infections. Special attention is given to the role of Treg in the modulation of gastric inflammation induced by Helicobacter pylori infection. Findings in both experimentally infected mice and humans with natural infection indicate that Treg are important in protecting the H. pylori-infected host against excessive gastric inflammation and disease symptoms but on the negative side promote bacterial colonization at the gastric and duodenal mucosa which may increase the risk in H. pylori-infected individuals to develop duodenal ulcers.     

A fungal powdery mildew pathogen induces extensive local and marginal systemic changes in the Arabidopsis thaliana microbiota

Powdery mildew is a foliar disease caused by epiphytically growing obligate biotrophic ascomycete fungi. How powdery mildew colonization affects host resident microbial communities locally and systemically remains poorly explored. We performed powdery mildew (Golovinomyces orontii) infection experiments with Arabidopsis thaliana grown in either natural soil or a gnotobiotic system and studied the influence of pathogen invasion into standing natural multi-kingdom or synthetic bacterial communities (SynComs). We found that after infection of soil-grown plants, G. orontii outcompeted numerous resident leaf-associated fungi while fungal community structure in roots remained unaltered. We further detected a significant shift in foliar but not root-associated bacterial communities in this setup. Pre-colonization of germ-free A. thaliana leaves with a bacterial leaf-derived SynCom, followed by G. orontii invasion, induced an overall similar shift in the foliar bacterial microbiota and minor changes in the root-associated bacterial assemblage. However, a standing root-derived SynCom in root samples remained robust against foliar infection with G. orontii. Although pathogen growth was unaffected by the leaf SynCom, fungal infection caused a twofold increase in leaf bacterial load. Our findings indicate that G. orontii infection affects mainly microbial communities in local plant tissue, possibly driven by pathogen-induced changes in source-sink relationships and host immune status.     

Sequencing the genome of Marssonina brunnea reveals fungus-poplar co-evolution

ABSTRACT: BACKGROUND: The fungus Marssonina brunnea is a causal pathogen of Marssonina leaf spot that devastates poplar plantations by defoliating susceptible trees before normal fall leaf drop. RESULTS: \We sequence the genome of M. brunnea with a size of 52 Mb assembled into 89 scaffolds, representing the first sequenced Dermateaceae genome. By inoculating this fungus onto a poplar hybrid clone, we investigate how M. brunnea interacts and co-evolves with its host to colonize poplar leaves. While a handful of virulence genes in M. brunnea, mostly from the LysM family, are detected to up-regulate during infection, the poplar down-regulates its resistance genes, such as nucleotide binding site domains and leucine rich repeats, in response to infection. From 10,027 predicted proteins of M. brunnea in a comparison with those from poplar, we identify four poplar transferases that stimulate the host to resist M. brunnea. These transferas-encoding genes may have driven the co-evolution of M. brunnea and Populus during the process of infection and anti-infection. CONCLUSIONS: Our results from the draft sequence of the M. brunnea genome provide evidence for genomegenome interactions that play an important role in poplar-pathogen co-evolution. This knowledge could help to design effective strategies for controlling Marssonina leaf spot in poplar.     

Asymptomatic Cattle Naturally Infected with Mycobacterium bovis Present Exacerbated Tissue Pathology and Bacterial Dissemination

Rational discovery of novel immunodiagnostic and vaccine candidate antigens to control bovine tuberculosis (bTB) requires knowledge of disease immunopathogenesis. However, there remains a paucity of information on the Mycobacterium bovis-host immune interactions during the natural infection. Analysis of 247 naturally PPD+ M. bovis-infected cattle revealed that 92% (n = 228) of these animals were found to display no clinical signs, but presented severe as well as disseminated bTB-lesions at post-mortem examination. Moreover, dissemination of bTB-lesions positively correlated with both pathology severity score (Spearman r = 0.48; p<0.0001) and viable tissue bacterial loads (Spearman r = 0.58; p = 0.0001). Additionally, granuloma encapsulation negatively correlated with M. bovis growth as well as pathology severity, suggesting that encapsulation is an effective mechanism to control bacterial proliferation during natural infection. Moreover, multinucleated giant cell numbers were found to negatively correlate with bacterial counts (Spearman r = 0.25; p = 0.03) in lung granulomas. In contrast, neutrophil numbers in the granuloma were associated with increased M. bovis proliferation (Spearman r = 0.27; p = 0.021). Together, our findings suggest that encapsulation and multinucleated giant cells control M. bovis viability, whereas neutrophils may serve as a cellular biomarker of bacterial proliferation during natural infection. These data integrate host granuloma responses with mycobacterial dissemination and could provide useful immunopathological-based biomarkers of disease severity in natural infection with M. bovis, an important cattle pathogen.     

Experimental bath infection with Flavobacterium psychrophilum, inducing typical signs of rainbow trout Oncorhynchus mykiss fry syndrome

Flavobacterium psychrophilum infection in salmonid fish, known as rainbow trout fry syndrome (RTFS) or bacterial coldwater disease (BCWD), is widespread in fish farms and natural waters. Despite many studies in which attempts at infection were made, an adequate method of infection has not yet been established. In this study, we evaluated a bath infection method in which we used bacteria at different stages of growth in the infection of rainbow trout Oncorhynchus mykiss. Rainbow trout with a mean body weight of 1.3 or 5.6 g, respectively, were infected by immersion in a bacterial suspension at different stages of growth (18 to 66 h shaking culture at 15 degrees C). The fish immersed in a logarithmic phase culture showed higher mortality than those in other culture phases. Indeed, 1.3 and 5.6 g fish showed typical clinical signs including ulcerative tissue of the trunk and lack of caudal fin edge. F. psychrophilum was detected by immunohistochemistry (IHC) in these tissue samples. These results indicate that experimental bath infection using a logarithmic phase bacterial solution is the most appropriate method for studies of infectious mechanisms.     

An infectious aetiology of sudden infant death syndrome

Due attention has been given to infectious agents and immune responses to infection in sudden infant death syndrome (SIDS). It has been acknowledged that the pathological, epidemiological and genotypic findings in SIDS infants suggest an infectious aetiology possibly being potentiated by immunoregulatory polymorphisms, however, the cause of SIDS is a mystery and remains open to debate. Consistent pathological findings are seen which display similarities to the pathogenesis of toxaemic shock and/or sepsis. The major risk factors for SIDS parallel those for increased colonization and serious bacterial infections and the natural variation in the incidence of SIDS cases is typical of an infectious disease. The roles played by viral infection, immunoregulatory genes and suspected bacterial species are discussed herein.     

吉林通化地区杨树栽培的生态区划

选取通化地区与杨树生长有密切关系的、具典型代表和鲜明时空分布规律的气候因子和自然地理因子作为统计指标,运用聚类分析方法对全区林业生态环境进行分类区划,划分为4个气候小区;调查全区26个引种的杨树生长状况,重点针对其抗寒性进行分类分级;针对杨树新品种与该地区环境适应性关系,确定杨树栽培的生态区划结果,并对每一气候小区的特殊情况具体分析,提出杨树引种栽培的科学依据．     

Isolation and characterization of a new Burkholderia pyrrocinia strain JK-SH007 as a potential biocontrol agent

Poplar canker is a kind of serious disease of poplar branches in China and all over the world. In China, the poplar canker is mainly caused by three pathogens of Cytospora chrysosperma, Phomopsis macrospora and Fusicoccum aesculi, which is hard to control. A collection of 1,013 bacterial isolates obtained from the poplar stems in 9 regions of China. Of all the strains tested, 13 bacterial isolates inhibiting three pathogens (C. chrysosperma, P. macrospora and F. aesculi) growth were selected, whose inhibition zone width were more than 15 mm. Strain JK-SH007 exhibited the most obvious antagonistic activity. Besides, this strain also produced extracellular hydrolytic enzymes (β-1, 3-glucanases, proteases and chitinases). This bacterium had no pathogenicity and was identified as Burkholderia cepacia complex (Bcc) genomovar IX: B. pyrrocinia by the Biolog identification system combined with 16S rDNA and recA gene sequence analysis and morphological, physiological and biochemical methods characteristics. B. pyrrocinia JK-SH007 exhibited the highest biocontrol and colonization capabilities. After 3 months, plant height and ground diameter in poplar seedlings inoculated with JK-SH007 were significantly (P < 0.05) higher than in control (non-inoculated) plants. The selected B. cepacia isolate colonized poplar stems and leaves endophytically, promoting plant growth and suppressing pathogenic activities of C. chrysosperma, P. macrospora and F. aesculi on seedling of poplar. This is one of the few reports dealing with isolation and characterization of B. cepacia strains with biocontrol activity against the poplar canker. The endophytic isolate also has the potential to perform as plant growth promoter.     

Molecular mimicry mediated by MHC class Ib molecules after infection with gram-negative pathogens

The development of many autoimmune diseases has been etiologically linked to exposure to infectious agents. For example, a subset of patients with a history of Salmonella infection develop reactive arthritis. The persistence of bacterial antigen in arthritic tissue and the isolation of Salmonella or Yersinia reactive CD8+ T cells from the joints of patients with reactive arthritis support the etiological link between Gram-negative bacterial infection and autoimmune disease. Models proposed to account for the link between infection and autoimmunity include inflammation-induced presentation of cryptic self-epitopes, antigen persistence and molecular mimicry. Several studies support molecular mimicry as a mechanism for the involvement of class II epitopes in infectious disease-induced self-reactivity. Here, we have identified an immunodominant epitope derived from the S. typhimurium GroEL molecule. This epitope is presented by the mouse H2-T23-encoded class Ib molecule Qa-1 and was recognized by CD8+ cytotoxic T lymphocytes induced after natural infection. S. typhimurium-stimulated cytotoxic T lymphocytes recognizing the GroEL epitope cross-reacted with a peptide derived from mouse heat shock protein 60 and recognized stressed macrophages. Our results indicate involvement of MHC class Ib molecules in infection-induced autoimmune recognition and indicate a mechanism for the etiological link between Gram-negative bacterial infection and autoimmunity.     

Pseudomonas viridiflava and P. syringae--natural pathogens of Arabidopsis thaliana

We report the isolation and identification of two natural pathogens of Arabidopsis thaliana, Pseudomonas viridiflava and Pseudomonas syringae, in the midwestern United States. P. viridiflava was found in six of seven surveyed Arabidopsis thaliana populations. We confirmed the presence in the isolates of the critical pathogenicity genes hrpS and hrpL. The pathogenicity of these isolates was verified by estimating in planta bacterial growth rates and by testing for disease symptoms and hypersensitive responses to A. thaliana. Infection of 21 A. thaliana ecotypes with six locally collected P. viridiflava isolates and with one P. syringae isolate showed both compatible (disease) and incompatible (resistance) responses. Significant variation in response to infection was evident among Arabidopsis ecotypes, both in terms of symptom development and in planta bacterial growth. The ability to grow and cause disease symptoms on particular ecotypes also varied for some P. viridiflava isolates. We believe that these pathogens will provide a powerful system for exploring coevolution in natural plant-pathogen interactions.     

杨树三倍体选育研究进展

杨树三倍体具有速生,纤维长等特点,是速生短周期纸浆材的首选树种,本文从发现树天然三倍体,人工培养杨树三倍体,特别是采用杂交,筛选天然2n花粉,人工诱导2n配子方法培育三倍体等方面,对杨树三倍体的育种研究现状进行了综述,指出了杨树三倍体育种的发育方向及意义。     

杨树三倍体选育研究进展

杨树三倍体具有速生、纤维长等特点,是速生短周期纸浆材的首选树种。本文从发现杨树天然三倍体,人工培育杨树三倍体,特别是在采用杂交、筛选天然2n花粉、人工诱导2n配子方法培育三倍体等方面,对杨树三倍体的育种研究现状进行了综述,指出了杨树三倍体育种的发展方向及意义。     

四霉素防治杨树溃疡病田间应用研究

杨树溃疡病是在杨树上发生普遍且危害严重的干部病害。为了有效控制杨树溃疡病的发生,利用四霉素制剂对杨树溃疡病进行田间防治试验。结果表明,于春季杨树溃疡病发生初期开始施药防治,采用刮涂法施药,0.3%四霉素水剂对杨树溃疡病有较好的防治效果,推荐使用量为有效成分60~300 mg/kg(稀释倍数10~50),防效为62.9%~77.4%。试验期间林间系统观察表明,0.3%四霉素水剂在试验浓度范围内对杨树生长发育无不良影响。     

Transcriptome Analysis of Poplar during Leaf Spot Infection with Sphaerulina spp.

Diseases of poplar caused by the native fungal pathogen Sphaerulina musiva and related species are of growing concern, particularly with the increasing interest in intensive poplar plantations to meet growing energy demands. Sphaerulina musiva is able to cause infection on leaves, resulting in defoliation and canker formation on stems. To gain a greater understanding of the different responses of poplar species to infection caused by the naturally co-evolved Sphaerulina species, RNA-seq was conducted on leaves of Populus deltoides, P. balsamifera and P. tremuloides infected with S. musiva, S. populicola and a new undescribed species, Ston1, respectively. The experiment was designed to contain the pathogen in a laboratory environment, while replicating disease development in commercial plantations. Following inoculation, trees were monitored for disease symptoms, pathogen growth and host responses. Genes involved in phenylpropanoid, terpenoid and flavonoid biosynthesis were generally upregulated in P. balsamifera and P. tremuloides, while cell wall modification appears to play an important role in the defense of P. deltoides. Poplar defensive genes were expressed early in P. balsamifera and P. tremuloides, but their expression was delayed in P. deltoides, which correlated with the rate of disease symptoms development. Also, severe infection in P. balsamifera led to leaf abscission. This data gives an insight into the large differences in timing and expression of genes between poplar species being attacked by their associated Sphaerulina pathogen.