猕猴桃细菌性花腐病及其防治

我国猕猴桃大规模商品化栽培已有20多年历史, 同其他作物一样,随着从野生到大面积人工栽培的时间延长, 其病虫害种类和发病程度呈现复杂化趋势.湖北省是猕猴桃原生地分布省份之一, 现人工栽培面积达2 000 hm2.     

玉米细菌性叶斑病-上升中的玉米病害

2003-2008年,从全国21个省（自治区、直辖市）采集玉米细菌性叶斑病材料,先后分离并保存了187株病原物,根据病原物在NA培养基上的菌落特征,可将病菌分为黄色圆形菌落、白色圆形菌落和乳白色不规则形菌落3类。根据调查数据和初步研究结果,将目前我国发生的玉米细菌性叶斑病归纳为4种主要症状类型：枯死斑型、褪绿斑型、条斑型和褐斑型。鉴于我国玉米细菌性叶斑病呈现逐年加重的趋势,对我国玉米生产具有潜在威胁,本文对玉米细菌性叶斑病提出了防治建议。     

Bacterial wilt disease: Host resistance and pathogen virulence mechanisms

Bacterial wilt (BW), caused by Ralstonia solanacearum, is one of the most destructive bacterial diseases of Solanaceous species worldwide. The species infects plants in more than 200 species and 50 families and was ranked second in a list of the top 10 most scientifically and economically important bacterial plant pathogens [1]. The molecular mechanisms underlying resistance and the functions of R. solanacearum effectors are beginning to be uncovered, and much remains to be discovered. In this mini-review, we provide a summary of host resistance and R. solanacearum virulence mechanisms, with a focus on tomato.     

Plectosphaerella rot of lettuce, coriander, and chervil caused by Plectosphaerella pauciseptata

Rot diseases of hydroponically cultured leaf lettuce, coriander, and chervil were found in Chiba Prefecture, Japan. Stems and petioles of the three diseased plants became brown or black with a soft rot, and vascular parts of the stems became discolored. Seemingly similar fungi were isolated from the diseased plants. Pathogenicity of these fungal isolates to each plant was demonstrated by inoculation tests. The fungi were identified as Plectosphaerella pauciseptata based on morphological and cultural characters. This identification was supported by phylogenetic analysis with rDNA ITS1-5.8S-ITS2 regions. The diseases were named Plectosphaerella rot (Plectosphaerella huhai-byo in Japanese) of lettuce, coriander, and chervil.     

<Emphasis Type="Italic">Alternaria alternata</Emphasis>: A new seed-transmitted disease of coriander in South Africa

This is the first report of Alternaria leaf spot disease on coriander (Coriandrum sativum L.) in South Africa. Using the agar plate method, Alternaria alternata was isolated from coriander seed lots together with four other fungal genera, which included Aspergillus, Fusarium, Penicillium and Rhizopus. Standard seed germination tests of coriander seed lots infected with seed-borne mycoflora showed a positive correlation with the number of diseased seedlings (r?=?0.239, p?<?0.01). Pathogenicity tests demonstrated that this seed-borne A. alternata was pathogenic on coriander and symptoms on leaves first appeared as small, dark brown to black, circular lesions (<5 mm diam.) that enlarged and coalesced to form dark brown blotches as time progressed. Leaf spot disease was most severe (64%) on wounded leaves inoculated with A. alternata. Re-isolation of A. alternata from diseased coriander plants satisfied the Koch’s postulates, thus confirming it as the causal agent of Alternaria leaf spot disease. Parsimony analysis based on rpb2 (GenBank Accession No. KT895947), gapdh (KT895949) and tef-1α (KT895945) sequences confirmed identity of the Alternaria isolate, which grouped within the A. alternata clade. Alternaria alternata was shown to be transmitted from infected coriander seed to the developing plants.     

Bacterial antagonists and their cell-free cultures efficiently suppress canker disease in citrus lime

Journal of Plant Diseases and Protection - Proliferation of citrus canker disease caused by Xanthomonas citri subsp. citri (Xcc) has increasingly become a serious threat and has resulted in a...     

Bacterial fruit blotch of melon: screens for disease tolerance and role of seed transmission in pathogenicity

Bacterial fruit blotch (BFB) of cucurbits, caused by Acidovorax avenae subsp. citrulli, is a serious threat to the watermelon and melon industries. To date, there are no commercial cultivars of cucurbit crops resistant to the disease. Here we assessed the level of tolerance to bacterial fruit blotch of various commercial cultivars as well as breeding and wild lines of melon, using seed-transmission assays and seedling-inoculation experiments. Selected cultivars were also tested in a greenhouse experiment with mature plants. All tested cultivars/lines were found to be susceptible to the pathogen, and most of them showed different responses (relative tolerance vs. susceptibility) in the different assays; however, some consistent trends were found: cv. ADIR339 was relatively tolerant in all tested assays, and cv. 6407 and wild lines BLB-B and EAD-B were relatively tolerant in seed-transmission assays. We also provide evidence supporting a strong correlation between the level of susceptibility of a cultivar/line and the ability of the pathogen to adhere to or penetrate the seed. To the best of our knowledge, this is the first attempt to assess melon cultivars/lines for bacterial fruit blotch response.     

Bacterial Diseases of Cassava

Abstract

Recent developments on the identities of the causal agents of bacterial diseases of cassava throughout the world are discussed.     

Bacterial biodegradation of ethoxylated surfactants

Agricultural, industrial and domestic use of surfactants leads to the entry of these compounds into terrestrial and aquatic ecosystems. Synthetic surfactants vary significantly in structure, but most consist of alkyl or alkylphenol groups attached to nonionic or anionic hydrophilic moieties. Continued use of these compounds is usually justified on the basis that they do not cause pollution problems because they undergo biodegradation by micro-organisms present in soils and surface waters. In accomplishing biodegradation, micro-organisms, predominantly bacteria, are exploiting these potentially useful resources of reduced carbon to derive energy and support growth in situations which are otherwise frequently oligotrophic. This paper reviews aspects of surfactant biodegradation, especially in relation to alcohol and alkylphenol ethoxylates used extensively as adjuvants for agrochemicals. In principle, bacteria can employ two strategies to gain access to the aliphatic chains in alcohol ethoxylate surfactants: separation of the hydrophobic chain from the hydrophile (central fission), or direct attack on the -terminal of the alkyl chain of the intact surfactant. Direct exo-cleavage of ethylene glycol units from the polyethylene glycol (PEG) chain also provides a third route to assimilable carbon. In pure cultures of known degraders or in mined environmental samples, all three strategies are exploited, some even within the same organism. Central fission occurs predominantly at the alkyl-ether bond, but may also occur within the PEG chain itself, thus producing various glycol intermediates which accumulate in pure cultures but appear only transiently in mixed environmental samples. Against this background, the relative resistance of some alkylphenol ethoxylates to biodegradation can be assessed in mechanistic terms. The steric bulk of the aryl nucleus effectively eliminates the central fission pathway. Moreover, some alkyl phenol ethoxylates contain branched alkyl chains which restrict ω-β-oxidation. As a result, ethoxylate shortening appears to be the major course of biodegradation observed so far. Not surprisingly, these surfactants are observed to undergo extensive primary biodegradation (removal of surfactant properties) but relatively restricted ultimate degradation to carbon dioxide and normal cell components.     

First report of coriander leaf blight diseases caused by Cladosporium tenuissimum in China and analysis of metabolic alterations related to pathogenic processes

Coriander (Coriandrum sativum) is a medicinal and aromatic plant. From November 2017 to March 2020, leaf blight disease on coriander plants was frequently observed in commercial coriander cultivated fields of Haikou, Sanya and Wanning City, Hainan Province, China. Leaves with symptoms showed irregular chlorotic to dark brown necrotic lesions at the edges of leaves, and the leaves were curled and covered with a layer of grey mould. Based on morphological characteristics, pathogenicity testing and concatenated sequences of the internal transcribed spacer region (ITS), actin (ACT) and translation elongation factor-1α (TEF) genes, the pathogen was identified as Cladosporium tenuissimum. Untargeted metabolomes of the coriander leaves were analysed by gas chromatography-mass spectrometry (GC-MS). Score plots of principal component analysis (PCA) and partial least squares discriminant analysis (PLS-DA) showed clear discrimination between infected and control treatments. The levels of l -threonic acid, hexadecanoic acid and myo-inositol in the control treatment were 3.45-, 1.81- and 2.44-fold, respectively, those in the infected treatment. To our knowledge, this is the first report of C. tenuissimum causing coriander leaf blight disease in China. Furthermore, this study indicates that C. tenuissimum infection of coriander causes a significant decrease in l -threonic acid, hexadecanoic acid and myo-inositol levels, indicating that these metabolites may be involved in the plant's response to coriander leaf blight disease.     

Bacterial pathogens of rice in the Kingdom of Cambodia and description of a new pathogen causing a serious sheath rot disease

A study of rice diseases in Cambodia from 2005 to 2007 showed widespread occurrence of diseases caused by Acidovorax avenae subsp. avenae, Burkholderia gladioli, B. cepacia and Pantoea ananatis. This is the first report of these pathogens in Cambodia. Additionally, a pseudomonad causing a widespread disease similar to sheath brown rot (caused by Pseudomonas fuscovaginae) was isolated. The studied strains were pathogenic to rice cvs Sen Pidau and IR 66, producing similar, though slightly less severe, symptoms to those observed in the field. Based on comparative 16S rDNA gene sequence analysis, combined with cell wall fatty acid analysis and metabolic profiles, the isolated strains were allocated to the genus Pseudomonas. The novel species were differentiated from Pseudomonas fuscovaginae and P. putida by their inability to metabolize d ‐fructose, d ‐galactose, d ‐galactonic acid lactone, d ‐galacturonic acid, d ‐glucosaminic acid, d ‐glucuronic acid, p‐hydroxy phenylacetic acid, d ‐saccharic acid and urocanic acid. The major fatty acids were C_16:0, summed feature 3 (C_16:1ω7c and C_16:1ω6c) and summed feature 8 (C_18:1ω7c), representing 80% of the total. Partial 16S rRNA gene sequences (1460 bp) were identical, except for two nucleotide changes amongst the six strains. Alignment of the causal strains within type‐culture databases revealed similarities of 99·7% with Pseudomonas parafulva AJ 2129^T, 99·2% with P. fulva IAM 1592^T, 98·9% with P. plecoglossicidia FPC 951^T, and 98·1% with P. fuscovaginae MAFF 301177^T. On the basis of data from this polyphasic study, it is proposed that the unknown strains isolated from rice represent a novel species of the genus Pseudomonas.     

北京地区番茄青枯病健康和发病植株根际细菌群落比较分析

本研究利用高通量测序技术研究了北京地区番茄青枯病健康与发病植株根际细菌组成差异,构建相关性网络,并从健康植株根际分离和筛选青枯菌拮抗菌群。结果显示,pH和速效磷是影响各采样地区土壤细菌群落组成的主要因子;发病植株根际土壤群落结构比健康植株更复杂,群落间相互作用数量增多;网络分析表明有15个属与Ralstonia直接相关;通过拮抗实验获得14株对青枯菌具有显著拮抗能力的根际细菌,其中包括3个不常见拮抗细菌类群,为无色杆菌属Achromobacter、剑菌属Ensifer和赖氨酸芽胞杆菌属Lysinibacillus。该研究结果为北京地区番茄青枯病预警和防控提供了理论基础和资源储备。     

Bacterial Blight of Cotton in Sudan

Abstract

This paper is in effect a summary of three COPR reports (Pope, 1973 and 1974, Pope and Watt, 1975) which is intended to give the reader an indication of possible uses for light hovercraft under field conditions both in the United Kingdom and overseas. Some suggestions are made as to possible uses and various forms of equipment and modifications are described and discussed.     

Bacterial soft rot of Agaricus bitorquis

A new pathovar of Pseudomonas gladioli, pv. agaricicola is described to accommodate a bacterium pathogenic to Agaricus bitorquis. The bacterium causes a rapid soft rot of cultivated mushrooms at temperatures above 25 C. The pathotype culture has been deposited at the National Collection of Plant Pathogenic Bacteria, Harpenden, UK and designated NCPPB 3580.     

Cassava Bacterial Blight in Uganda

Abstract

Cassava bacterial blight (CBB) is a major problem of cassava in Uganda. It was first recorded in Terego County, Nile Province in 1976, and a disease survey indicated that CBB is now present in over half of the country. Losses of 90–100% have been observed on susceptible varieties in parts of the Nile, North and Eastern provinces. Symptoms include angular leaf spots, blight, wilt dieback and gum exudations. Planting of infected materials, rainfall, hailstorms, wind and insects are major factors in the spread of the disease. Restriction of movement of infected cassava cuttings to non-infected areas, planting of resistant varieties and healthy cuttings, encouragement of mixed cropping and crop rotation are recommended for control.     

Symptoms of a Bacterial Disease of Neem

Abstract

A bacterial disease of neem causing angular leaf spot, shot-hole and vein blight symptoms was found to occur in a severe form in parts of Rajasthan (India). The causal organism was found to be a species of Pseudomonas. Studies revealed that prevailing temperature had a decisive influence on the manifestations of symptoms. Shot-hole appeared to be a defence reaction operating in leaf tissues against parasitic attack. The development of vein blight symptoms might play an important role in the perpetuation of disease from season to season.     

魔芋软腐病综合防治技术

魔芋软腐病的大发生与土壤、温度、湿度(雨量、土壤含水量)、肥料(种类、数量)及栽培模式等因素密切相关。魔芋在长期的进化过程中,自然形成了需要低温(15℃～19℃)、凉爽、湿润无渍害、弱光照的生理特性。要求土壤疏松肥沃,以有机肥为主,养分平衡供给的生产条件,若违背了客观存在的基本条件,软腐病就会大面积发生,造成严重的经济损失。(株死亡率20％～80％)。如果能满足这些客观条件,就能有效的抑制软腐病等病虫害的大发生,获得较高的产量,创造较大的经济价值,达到高产高效的目的。