柑桔溃疡病生防细菌Bt8的研究

柑桔溃疡病是中国柑桔的重要病害。从南宁柑桔园土壤中分离到1株对柑桔溃疡病菌具有强抑制力的细菌Bt8。根据Bt8菌株的形态1、6S rDNA序列分析以及生理生化特性,将其鉴定为鲍氏不动杆菌。Bt8菌株的抑菌效果受温度、pH及培养基等环境因素的影响。在温室条件下将该细菌悬浮液喷施到柑桔叶片上,获得了55.2%的病斑抑制效果。研究结果揭示了鲍氏不动杆菌在柑桔溃疡病田间防治上的潜能。     

Finger printing of acid lime varieties and clones having varied resistance to bacterial canker,using RAPD marker

Citrus is an important fruit crop having divergent genetic variation within the species. The germplasm identification and characterisation is an important link between the conservation and utilisation of genetic resources. Conventionally, variety/clone identification has relied on morphological characters such as growth habit, leaf, floral and fruit characters etc. Investigation through RAPD (random amplified polymorphic DNA) markers was carried out for determination of genetic variation among 12 acid lime clones having varied resistance to bacterial canker disease. DNA was extracted from the leaf of 12 acid lime clones and was subjected to PCR using 20 random primers (nine from OPM and 11 from OPA series) which yielded a total of 127 distinct DNA fragments, out of which 103 were polymorphic. Genetic similarity was evaluated based on the presence or absence of bands. The bands obtained were polymorphic, with sizes ranging from 750 bp to 2.5 kb. Cluster analysis using the similarity coefficient showed that the Balaji, RHRL-124 and PKM-1 formed one cluster and the remaining clones formed a second cluster, which in turn were divided into TAL 94-9, TAL 94-10, TAL 94-11 and TAL 94-12 which formed the first subcluster; the Nalgonda selection and local acid lime formed a second subcluster; TAL 94-8, RHRL-49 and RHRL-122 did not resemble any other clones. Among the 12 acid lime clones, Balaji, RHRL-124, RHRL-122 and PKM-1 were found to be moderately resistant to bacterial canker. Correlation of RAPD data with canker disease incidence in the moderately resistant acid lime clones viz., Balaji, RHRL-124 and PKM-1 were formed as one cluster, and all susceptible clones formed as a second cluster viz., except TAL-94-9, RHRL-122, which were found to be moderately resistant and did not form a cluster with any other acid lime clone.     

广西柑橘溃疡病菌菌系分化研究

从广西北海、桂林地区11个柑橘品种溃疡病材料上分离得到13株致病菌,进行菌系分化研究表明:在所测试的35项生理特征中有25项(柠檬酸盐、丙二酸盐、36℃生长、耐盐性(1～3%)、吐温20、吐温80、水杨素、卫茅醇、葡萄糖、乳糖、纤维二糖、苯丙氨酸、棉子糖、松三糖、侧金盏花醇、菊糖、核糖、甘露醇、阿拉伯糖、海藻糖、蜜二糖、山梨糖、七叶苷、酒石酸盐、明胶)完全相同,10项(醋酸盐、果糖、枸橼酸盐、鼠李糖、木糖、蔗糖、麦芽糖、半乳糖、淀粉、甘露糖)存在差异;16项生化特征测试中有12项(细胞色素C氧化酶、过氧化氢酶、甲基红试验、乙酰甲基甲醇试验、水解七叶苷、果聚糖产生、硝酸盐还原、脲酶、苯丙氨酸脱氨酶、精氨酸双水解酶、卵磷脂酶、明胶水解)完全相同,4项(水解淀粉、吲哚产生、硫化氢产生、石蕊牛奶)存在差异;3种噬菌体鉴定试验能够区分出13个菌株菌系分化现象的存在,且分为6种敏感型,而菌株细胞脂肪酸成分分析则不能区分菌系分化情况。     

猕猴桃溃疡病流行的生态因子及药剂对病菌的抑菌作用

经5年系统研究得出,影响猕猴桃溃疡病发生流行的特点是,海拔750m以上的果园发病重,向阳坡发病重于背阳坡,不同品种发病差异显著,金丰品种易感病,金魁品种高度抗病;树龄越大,病株率越高;不同枝龄比较,一年生枝条病枝死亡率和枝条死亡率最高.6种药剂以加瑞农和硫酸链霉素抑菌效果最好.     

改造农田小生境,增加天敌,抑制病虫

湖北省郧阳地区位于东经109°50′—111°50′,北纬31°30′—33°25′之间,处在世界陆地动物古北界与东洋界混合地带的西沿中部,利于这两界的天敌昆虫交互来往和生息繁衍。该地区又是我国东部平原西部山区过渡阶梯的典型地段,西北和西南山岭高竣重叠,海拔2,500米以上的山峰有7座,最高的达3,054米,阻挡了北来的冷空气。全年大风日数在10天以内,大风强度一般为5—7级,是湖北省大风日数最少、强度最弱的地区之一。风小既便于南下北上的天敢昆虫落脚     

猕猴桃溃疡病流行的生态因子及经剂对病菌的抑菌作用

经5年系统研究得出,影响猕猴桃溃疡病发生流行的特点是,海拔750m以上的果园发病重,向阳坡发病重于背阳坡,不同品种发病差异显著,金丰品种易感病,金魁品种高度抗病;树龄越大,病株率越高;不同枝龄比较,一年生村以条病枝死亡率和枝条死亡率最高.6种药剂以加瑞农和硫酸链霉素抑菌效果最好。     

Cloning and characterization of receptor kinase class disease resistance gene candidates in Citrus

The rice gene Xa21 represents a unique class of plant disease resistance (R) genes with distinct protein structure and broad-spectrum specificity; few sequences or genes of this class have been cloned and characterized in other plant species. Degenerate primers were designed from the conserved motifs in the kinase domains of Xa21 and tomato Pto, and used in PCR amplification to identify this class of resistance gene candidate (RGC) sequences from citrus for future evaluation of possible association with citrus canker resistance. Twenty-nine RGC sequences highly similar to the kinase domain of Xa21 (55%–60% amino-acid identity) were cloned and characterized. To facilitate recovery of full-length gene structures and to overcome RGC mapping limitations, large-insert genomic clones (BACs) were identified, fingerprinted and assembled into contigs. Southern hybridization revealed the presence of 1–3 copies of receptor-like kinase sequences (i.e., clustering) in each BAC. Some of these sequences were sampled by PCR amplification and direct sequencing. Twenty-three sequences were thus obtained and classified into five groups and eight subgroups, which indicates the possibility of enhancing RGC sequence diversity from BACs. A primer-walking strategy was employed to derive full-length gene structures from two BAC clones; both sequences 17o6RLK and 26m19RLK contained all the features of the rice Xa21 protein, including a signal peptide, the same number of leucine-rich-repeats, and transmembrane and kinase domains. These results demonstrate that PCR amplification with appropriately designed degenerate primers is an efficient approach for cloning receptor-like kinase class RGCs. Utilization of BAC clones can facilitate this approach in multiple ways by improving sequence diversity, providing full-length genes, and assisting in understanding gene structures and distribution.Communicated by P. Langridge     

Integration of Pseudomonas fluorescens and salicylic acid improves citrus canker disease management caused by Xanthomonas citri subsp citri-A*

The individual and combined effects of Pseudomonas fluorescens (Pf) and salicylic acid (SA) were investigated for control of citrus bacterial canker (CBC). Both treated plants with copper hydroxide and untreated ones were used as controls. Mexican lime (Citrus aurantifolia) seedlings were treated with SA at 10 mM, Pf and distilled water. Plants were initially inoculated with Xanthomonas citri subsp citri 72 h post treatments. Results indicated that the Pf and SA treatment controlled CBC more effectively compared to separately applying Pf or SA. The application of Pf in combination with SA significantly reduced lesion number per leaf (72%) and disease severity (84%). Significant changes in the activities of peroxidase and catalase were found. In conclusion, the integration of Pf with SA complements each other and can be applied to manage citrus canker disease in conjunction with other control programmes.     

Epidemiology of Pseudomonas syringae Pathovars Associated with Decline of Plum Trees in the Southwest of Germany

Plum decline was associated with Pseudomonas syringae pathovars syringae and morsprunorum in Baden‐Württemberg. The trunks of affected plum trees (Prunus domestica) were girdled by bacterial cankers resulting in sudden death of infected trees. Copper compounds that were applied extensively during leaf fall and bud burst, were not effective. A minority of P. syringae strains isolated from cankers on plum trees were moderately resistant, while most strains were sensitive to cupric ions. Invasions through blossoms, leaves and wounds during the vegetation period were limited to the infection sites and plum trees coped effectively with both P. syringae pathovars eliminating them eventually. Infections after dormancy including very rare leaf scar infections did not induce cankers on the trunk. However, infections of dormant trees through frost injuries, (pruning) wounds or non‐injurious ingress by freezing and thawing were serious, because they led to cankers girdling the trunk. Control strategies to manage plum decline have to be adapted to the disease cycle. They should concentrate on the dormant period beginning with early frosts in autumn and ending with bud burst.     

微生物防治猕猴桃细菌性溃疡病的研究进展

由丁香假单胞菌猕猴桃致病变种引发的猕猴桃细菌性溃疡病是一种毁灭性病害。相较于化学防治手段,利用微生物进行病害防治具有环境相容性高、可持续性强和不易使病原菌产生抗药性等显著优势。通过文献梳理,该文系统概述了猕猴桃细菌性溃疡病的病害特点、致病菌与传播途径、微生物生防菌的主要类群、核心生防机制,以及微生物在该病生物防治中的实际应用情况,旨在为猕猴桃细菌性溃疡病的可持续生物防控提供理论支撑与实践指导。结果表明:(1)生防微生物种类丰富。对猕猴桃细菌性溃疡病具有防控效果的微生物主要包括细菌、放线菌、真菌和噬菌体四大类。其中,细菌中的芽孢杆菌属与假单胞菌属以及放线菌中的链霉菌属应用最为广泛,防效显著。(2)生防机制有直接作用和间接作用两条路径。直接作用包括分泌抗菌肽、抗生素等抑菌物质以溶解病原菌细胞壁,通过营养竞争、空间占位以阻断病原菌的侵染位点,以及借助寄生作用直接破坏病原菌的菌体结构; 间接作用核心在于诱导寄主植物产生系统抗性,从而增强其对猕猴桃细菌性溃疡病的抵御能力。多数高效生防菌株兼具这两种作用机制,其防效优于单一作用机制的菌株。(3)同一研究中,复合微生物菌剂的防治效果与稳定性通常优于单一微生物。不同菌株间协同作用,不仅能拓宽抗菌谱,还能提升菌株在植株体表的定殖率与抗逆性。综上,该文明确指出了当前猕猴桃细菌性溃疡病生物防控领域存在的核心问题,并提出了具有针对性的建议。     

Xanthan is not essential for pathogenicity in citrus canker but contributes to<Emphasis Type="Italic"> Xanthomonas</Emphasis> epiphytic survival

Xanthan-deficient mutants of Xanthomonas axonopodis pv. citri, the bacterium responsible for citrus canker, were generated by deletion and marker exchange of the region encoding the carboxy-terminal end of the first glycosyltransferase, GumD. Mutants of gumD did not produce xanthan and remained pathogenic in citrus plants to the same extent as wild-type bacteria. The kinetics of appearance of initial symptoms, areas of plant material affected, and growth of bacteria inside plant tissue throughout the disease process were similar for both wild-type and mutant inoculations. Moreover, exopolysaccharide deficiency did not impair the ability of the bacteria to induce hypersensitive response on non-host plants. Apart from variations in phenotypic aspects, no differences in growth or survival under different stress conditions were observed between the xanthan-deficient mutant and wild-type bacteria. However, gumD mutants displayed impaired survival under oxidative stress during stationary phase as well as impaired epiphytic survival on citrus leaves. Our results suggest that xanthan does not play an essential role in citrus canker at the initial stages of infection or in the incompatible interactions between X. axonopodis pv. citri and non-host plants, but facilitates the maintenance of bacteria on the host plant, possibly improving the efficiency of colonization of distant tissue.     

噬菌体鸡尾酒对猕猴桃溃疡病的田间防治效果及叶际细菌群落结构的影响

【背景】噬菌体鸡尾酒可作为一种杀灭猕猴桃溃疡病病原菌(Pseudomonassyringaepv.actinidiae, Psa)的生物制剂,但关于噬菌体鸡尾酒在田间的防治效果和对猕猴桃植株叶际内生细菌群落结构影响的研究依然较少。【目的】探究噬菌体鸡尾酒在田间防控猕猴桃溃疡病的效果,以及噬菌体鸡尾酒对猕猴桃茎内叶际细菌微生态的影响。【方法】使用猕猴桃溃疡病病原菌感染健康植株,对比施用噬菌体鸡尾酒和传统铜制剂后溃疡病的发病情况,利用高通量测序技术分析猕猴桃叶际内生细菌群落结构的变化。【结果】与铜制剂相比,噬菌体鸡尾酒可更有效地控制猕猴桃溃疡病,改变叶际细菌群落的丰富度与多样性,增强群落结构的稳定性,改善群落物种功能基因丰度情况,一定程度使叶际细菌群落恢复至健康状态。【结论】噬菌体鸡尾酒在杀灭病原菌的同时具有良好的微生态调节功能,在猕猴桃溃疡病的生物防治中具有巨大的应用潜力。     

A phcA− marker-free mutant of Ralstonia solanacearum as potential biocontrol agent of tomato bacterial wilt

A phcA⁻ mutant of Ralstonia solanacearum strain ZJ3721 was created in a marker-free method. Expression of virulence-associated genes such as xpsR, egl, tek and epsE was significantly suppressed in the phcA⁻ mutant. The ability of the mutant to control tomato bacterial wilt was evaluated by potting experiment. Results showed that application of mutant with wild type (WT) at the same time only delayed the development of wilt for about one day and the population of WT in tomato rhizosphere soil was nearly 70-fold higher than that of the mutant, resulting in a 90% disease incidence at last, as high as that of control. If the phcA⁻ mutant was applied three days earlier than WT pathogen, tomato wilt disease incidence was only 6%, 80% lower than that of control and population of WT was about 0.5-fold as much as that of mutant. Under hydroponic conditions, phcA⁻ mutant significantly triggered the expressions of genes in salicylic acid pathway but inhibited the expressions of genes in jasmonic acid (JA) and ethylene (ET) pathways. The expressions of PR-1a and GluA genes (salicylic acid pathway) in phcA⁻ mutant were 66-fold and 7.5-fold higher than in WT pathogen after three days of inoculation.