Burkholderia gladioli associated with symptoms of bacterial grain rot and leaf-sheath browning of rice plants

Rice plants with bacterial leaf-sheath browning and grain rot were observed in Fukuoka Prefecture in Japan during the autumn seasons of 1995 and 1996. Burkholderia spp. were consistently isolated from the infected leaf sheaths and grains. These isolates were pathogenic and induced symptoms of seedling rot, grain rot, and leaf-sheath browning in rice plants, as well as in some orchidaceous plants (cymbidium, dendrobium, and oncidium leaves), gladiolus leaves, and onion bulbs. On the basis of morphological, physiological and pathological tests, and species-specific polymerase chain reaction, the isolates were identified as belonging to either Burkholderia glumae or Burkholderia gladioli. B. gladioli, as well as B. glumae, attacked rice plants after artificial inoculation and reproduced the symptoms similar to those after natural infections. We confirmed that rice is an additional natural host of B. gladioli. It is clarified that bacterial grain rot of rice is caused not only by B. glumae but also by B. gladioli.     

Effects of postharvest onion curing parameters on bulb rot caused by Pantoea agglomerans,Pantoea ananatis and Pantoea allii in storage

Crop loss of onion bulbs during storage carries an exceptionally high economic impact because a large portion of the production expenses has been expended before storage. Because of this, it is important to define practices that can reduce onion bulb losses caused by storage rots. This study investigates the impact of various curing parameters on disease development resulting from infection by Pantoea agglomerans, P. ananatis and P. allii on onion bulb cultivars Vaquero and Redwing, during storage. Overall, both the incidence and mean rot severity were similar amongst the bulbs under comparable conditions regardless of the species of Pantoea inoculated, although a significant difference was detected between the two onion bulb cultivars. In addition, a significant reduction of storage rot was observed when curing temperatures were ≤35°C. At temperatures >35°C, a shorter curing duration (2 days vs 14 days) decreased the severity of bulb rot due to Pantoea. This increased understanding of the inter‐relationships between the parameters used for curing, and the incidence and severity of bulb rot caused by Pantoea helps provide guidance towards using the curing process as a means to reduce the level of damage resulting from post‐harvest storage rot.     

Reduced volume application of fungicides for the control of onion rots

A survey was conducted to define the fungi population contaminating onion bulbs in Israel during three growing seasons. Significant rots were found to be caused byBotrytis allii, B. cinerea andAspergillus niger. All the onion stocks tested showed infections, but the severity and identity of the pathogens varied between seasons.B. cinerea andB. allii were the most prevalent fungi in winter-harvested onions. Species ofAspergillus, Penicillium, Fusarium, Rhizopus andTrichoderma were also isolated. The first two were the only species found on summer onions. High fungal contamination had been the main factor affecting an attempt to improve the storage quality and shelf life of the harvested bulbs. Chemical disinfection using a reduced-volume application (RVA) technique was efficient in controlling the major storage rots (caused byA. niger andB. cinerea) of the bulbs, without the major disadvantages of the dipping method. The rate of control was directly correlated with the cover density of the deposited fungicide, but not with the amount deposited. The RVA technique should enable prolongation of postharvest shelf life and storability of onion bulbs.     

Auftreten und Nachweis von Fusarium oxysporum und F. proliferatum an Steck- und Saatzwiebeln

The pathogen Fusarium oxysporum f. sp. cepae inducing the Fusarium basal rot mainly spreads in warmer cultivation regions due to its adaptibility to high temperature. Meanwhile the pathogen occurs in Germany as well, especially in years with relatively high average temperature during the growing season. Phytopathological investigations of 300 symptomless onion bulbs showed a contamination rate of approximately 10% with regard to Fusarium spp, with F.?oxysporum proving to be the predominant species. Onion sets planted in these fields were latently infected with F.?oxysporum at rates of 19?C98%. Unexpectedly, the contaminated sets did not indispensably lead to a high occurrence of plants exhibiting characteristic symptoms of Fusarium basal rot such as wet and dry rot. Presumably, the development of symptoms is particularly affected by given climatic conditions. The results of pathogenicity tests of isolated Fusarium spp. isolates under controlled conditions support this assumption. The inoculation of the substrate with selected Fusarium spp. isolates resulted in a reduction of emergence by up to 70% under controlled conditions, which are suboptimal with regard to the cultivation of onions. The emergence of plants was not affected by Fusarium spp. under optimal cultivation of onions. However, under optimal cultivation conditions a reduction of plant growth occurred in a subsequent growth stage. Beside F.?oxysporum, F.?proliferatum could be detected in onion bulbs as well as seeds. The proportion of contaminated seeds accounted to 62%. Both species F.?oxysporum and F.?proliferatum proved to be pathogenic in onion although their isolates varied much in their virulence.     

Fusarium proliferatum, an additional bulb rot pathogen of Chinese chive

This is the first report of a disease of Chinese chive caused by Fusarium proliferatum. Because the symptoms are similar to those of the bulb rot (kampu-byo in Japanese) caused by F. oxysporum, we propose F. proliferatum as another causal agent of bulb rot of Chinese chive. Symptoms are wilting of leaves and brown rot on the basal bulbs of Chinese chive. A Fusarium sp., frequently isolated from symptomatic plants, produced identical symptoms on Chinese chive after inoculation, and was reisolated from the diseased plants. The fungus was identified as F. proliferatum based on morphological, cultural, and molecular characteristics.     

A novel rhizobacterium Bk7 for biological control of brown sheath rot of rice caused by Pseudomonas fuscovaginae and its mode of action

The study presents the first report on biocontrol of brown sheath rot disease of rice caused by Pseudomonas fuscovaginae using rhizo-bacterial isolate Bacillus amyloliquefaciens Bk7. Four potential bioactive antagonists were selected from 120 Bacillus isolates. Results obtained from in vitro laboratory assay showed that rhizosphere bacterial strain Bk7 and its metabolites significantly suppressed the growth of Pseudomonas fuscovaginae with 93 % efficacy. In glasshouse experiments, strain Bk7 exhibited biocontrol efficacy of 76.6 % by reducing the disease incidence to 16.9 %, compared to 72.8 % observed in control treatment. In addition, the isolate Bk7 showed the growth promotion efficacy of plant height (GPE, 46.4 %) and fresh weight (GPE, 84.3 %). Characterization of isolate Bk7 revealed its strong capability for biofilm formation, inorganic phosphate solubilization and production of high amounts of Indole-3 acetic acid, siderophores and ammonia in vitro. Results obtained from multiplex PCR assay confirmed the presence of five lipopeptide biosynthetic gene markers (srfAA, fenD, bmyB, bacA and ituC) in the genome of strain Bk7. Moreover, Real-time qPCR of these genes demonstrated that surfactin, iturin and bacylisin coding genes were highly expressed in response to P. fuscovaginae exposure in vitro. Rhizosphere bacterial strain Bk7 was identified as B. amyloliquefaciens strain Bk7 based on the analysis of 16S rDNA internal transcribed spacer sequences and a fatty acid methyl ester analysis. The results obtained from this study showed the potential usefulness of Bk7 as a biocontrol agent in disease control of rice brown sheath rot.     

Response of different intermediate-day onion hybrids to natural infestation by Phoma terrestris and Fusarium oxysporum f. sp. cepae in Ciudad Real, Spain with assessment of different soil disinfestation methods

Incidence and severity of Pink root caused by Phoma terrestris and Fusarium basal rot caused by Fusarium oxysporum f. sp. cepae were field-tested on factorial combinations of different soil fumigation treatments in five different intermediate-day onion hybrids widely adapted at the Bola?os de Calatrava area (Ciudad Real, Spain). The effect of Dazomet and virulence of the local isolates were then tested in trays under greenhouse conditions. When compared to Electric, the other four onion hybrids showed a certain degree of tolerance to Pink root and Fusarium basal rot with little difference among them. The field trial carried out in 2006 showed significant but negligible beneficial effects in medium bulb weight and Pink root severity due to Dazomet. The field trial carried out in 2007 showed significant beneficial effects of Metham-sodium on plant growth and Pink root and Fusarium basal rot severities. Sodium tetrathiocarbonate performed worse than the control. Greenhouse test showed that Dazomet performed nearly as well as sterilization under controlled conditions. Virulence of local isolates was lower than that of reference isolates.     

Induction of resistance to Sclerotium rolfsii in different varieties of onion by inoculation with Trichoderma asperellum

We evaluated the ability of Trichoderma asperellum Samuels, Lieckfeldt & Nirenberg to induce resistance to the fungal plant pathogen, Sclerotium rolfsii Saccardo, in three onion (Allium cepa L.) varieties. Both the severity of disease and the activities of glucanase, chitinase and peroxidase (enzymes involved in plant resistance) were evaluated in onions inoculated with T. asperellum alone, S. rolfsii alone, or both T. asperellum and S. rolfsii (dual-inoculation) and compared to uninoculated (control) plants. In dual inoculations, the presence of T. asperellum reduced the severity of disease symptoms caused by S. rolfsii. Inoculation with T. asperellum alone increased glucanase, chitinase and peroxidase activity in bulbs, roots and leaves of all three onion varieties compared to uninoculated controls; bulbs of the variety Red Satan (RS) had the highest enzyme activity. In plants inoculated with S. rolfsii alone, enzyme activity was only increased in bulbs and roots compared to uninoculated controls. The highest levels of enzyme activity also occurred only in bulbs and roots of plants that had been dual-inoculated with T. asperellum and S. rolfsii. Plants of the RS variety showed the highest enzyme activities (both constitutive and induced) and showed the lowest severity of disease. Therefore, application of T. asperellum has potential as a biological control alternative to synthetic fungicides for protection of onion crops against infection by S. rolfsii. This protection depends on both constitutive and induced defence responses and varies amongst onion varieties.     

Occurrence of black rot of cultivated mushrooms (Flammulina velutipes) caused by Pseudomonas tolaasii in Korea

From black spots on winter mushroom (Flammulina velutipes), fluorescent bacteria were repeatedly isolated during surveys at places of production in the years 2009–2010 in Korea. From these lesions three bacterial strains (designated CHM13, CHM16, CHM17) were isolated which, following inoculation of mushroom stipes and caps, yielded characteristic black spots and sunken lesions, which developed into a severe black rot. Results of Gram stain and biochemical tests preliminarily identified these isolates as Pseudomonas tolaasii. This was confirmed by pathogenicity to winter mushroom, physiological and biochemical properties, analysis of the 16S rRNA and rpoB gene sequences, fatty acids profile, specific and sensitive PCR assays and, lipopeptide detection. This is the first report of the isolation of Pseudomonas tolaasii from cultivated winter mushroom in Korea.     

Studies on Botrytis spp. occurring on onions (Allium cepa) and leeks (Allium porrum)

Botrytis byssoidea (mycelial neck rot) was more prevalent than B. allii (sclerotial neck rot) on the leaves of field onions and the bulbs of stored onions grown in some of the areas where onions or onions and leeks had previously been grown sequentially.
B. byssoidea and B. porri were also isolated from leeks. Spores of B. allii, B. byssoidea (from onions and leeks), B. porri , and B. squamosa caused infection of seedlings of salad (green) and bulb onions.
Inoculation with B. squamosa spores caused severe infection of seedling leaves, but inoculation with mycelial discs caused little damage to onion bulb tissue. By comparison, mycelial discs of the remaining species were highly pathogenic to bulbs.
The practical implications of disease transfer of certain of these species between onions and leeks are discussed.     

Bacterial soft rot of myoga (Zingiber mioga) caused by Erwinia chrysanthemi

In 2010, a bacterial soft rot was found on myoga [Zingiber mioga (Thunb.) Rosc.] in Japan. Initial small spots on flower buds rapidly enlarged while changing from light brown to brown. Diseased flower buds became completely rotten. Several bacteria isolated from the diseased tissues caused the same symptoms as those observed in the fields and were reisolated from the tissue. These bacteria were identified as Erwinia chrysanthemi and were classified into subdivision IV and biovar 3. This is the first report of bacterial soft rot of myoga in the world.     

Clove-transmissibility of <Emphasis Type="Italic">Pseudomonas salomonii</Emphasis>, the causal agent of ‘Café au lait’ disease of garlic

Bacterial blight of garlic, caused by Pseudomonas salomonii, results in leaf and sheath necrosis and sometimes leads to soft rot and plant death. The epidemiology of this bacterial disease, known as ‘Café au lait’ disease, is poorly understood and no resistant cultivars are currently available. To develop control strategies for this disease, we investigated principal sources of inoculum. The pathogen was isolated from bulbs from plants with typical vegetative symptoms of bacterial blight. Subsequent development of typical foliar symptoms on plantlets originating from symptomatic bulbs demonstrated transmission of the pathogen in the planting material. In one of three field experiments the contamination rate of planting stock influenced the disease incidence in field-grown garlic. The importance of planting stock as a source of inoculum was demonstrated here and should be evaluated relative to other potential sources such as crop debris, soil or alternate hosts in order to develop successful control strategies.     

Occurrence of bacterial rot of onion bulbs caused by Burkholderia cepacia in Japan

In 2001, a bacterial rot of onion (Allium cepa L.) bulbs was observed in Japan. The causal agent was identified as Bukholderia cepacia (Palleroni & Holmes 1981 ex Burhkolder 1950) Yabuuchi, Kosako, Oyaizu, Yano, Hotta, Ezaki, and Arakawa 1993. The identified bacteria were divided into two groups (Y and W) based on colony colors, and several phenotypic and genetic characteristics. Based on recA polymerase chain reaction assays, the strains of the Y and W groups belong to genomovar I (B. cepacia sensu stricto) and genomovar III (B. cenocepacia), respectively.The nucleotide sequence data reported are available in the DDBJ/EMBL/GenBank databases under the accession numbers AB162427 and AB162428     

Fusarium oxysporum,F. proliferatum and F. redolens associated with basal rot of onion in Finland

In recent years in Finland, Fusarium infections in onions have increased, both in the field and in storage, and Fusarium species have taken the place of Botrytis as the worst pathogens causing post‐harvest rot of onion. To study Fusarium occurrence, samples were taken from onion sets, harvested onions and also from other plants grown in the onion fields. Isolates of five Fusarium species found in the survey were tested for pathogenicity on onion. Fusarium oxysporum was frequently found in onions and other plants, and, of the isolates tested, 31% caused disease symptoms and 15% caused growth stunting in onion seedlings. Fusarium proliferatum, a species previously not reported in Finland, was also identified. Over 50% of the diseased onion crop samples were infected with F. proliferatum, and all the F. proliferatum isolates tested were pathogenic to onion. Thus, compared to F. oxysporum, F. proliferatum seems to be more aggressive on onion. Also some of the F. redolens isolates were highly virulent, killing onion seedlings. Comparison of the translation elongation factor 1α gene sequences revealed that the majority of the aggressive isolates of F. oxysporum f. sp. cepae group together and are distinct from the other isolates. Incidence and relative proportions of the different Fusarium species differed between the sets and the mature bulbs. More research is required to determine to what extent Fusarium infections spoiling onions originate from infected onion sets rather than the field soil.     

Evaluation of chemical fungicides for control of onion white rot

Nine chemicals in 1976 and six in 1977 were evaluated in a five × five simple lattice design for control of Sclerotium cepivorum Berk., the causal agent of white rot of onions. The trial was conducted on organic muck soil in Burnaby, British Columbia, with uniform high levels of added (1976) or natural (1977) inoculum. The percentage of white rot infection, weight of healthy bulbs harvested and percentage of emergence were measured. There were significant differences, according to treatment, in the percentage of white rot infection of onion at harvest. Two chemicals, vinclozolin and iprodione, provided promising results as broadcast treatments on organic muck soils. A comparison of the results, in relation to differences in the distribution of inoculuin between the 1976 and 1977 trials, suggested that the major point of control may have been against mycelial growth through soil from sclerotia, remote to onion seedlings and/or from infected plants to healthy plants.     

Identification of differential resistance to six Fusarium oxysporum f. sp. cepae isolates in commercial onion cultivars through the development of a rapid seedling assay

Fusarium oxysporum isolates collected from onions in the UK and other countries were characterized using sequences of the transfer elongation factor 1‐α (TEF) gene and compared with published sequence data for 10 other isolates. Isolates associated with diseased onion bulbs in the UK formed two clades. Isolates from both clades were selected for pathogenicity testing and to develop a rapid seedling assay to screen commercial onion cultivars for resistance to F. oxysporum f. sp. cepae (FOC), the cause of basal rot. Differences in the levels of aggressiveness between isolates were observed and isolates from both clades were pathogenic. Differences in resistance/susceptibility were also observed amongst 10 commercial onion cultivars, with cvs Ailsa Craig Prizewinner and White Lisbon showing the highest levels of resistance. The results from the seedling assay were supported by those from a subsequent onion bulb rot assay. Thus, this study reports the development of a rapid, simple and repeatable seedling assay that can be used to screen large numbers of onion cultivars for resistance to FOC and which is indicative of resistance at the bulb stage.     

<Emphasis Type="Italic">Pseudomonas syringae</Emphasis> pv. <Emphasis Type="Italic">alliifistulosi</Emphasis> pv. nov., the causal agent of bacterial leaf spot of onions

In 1972, bacterial leaf spot of onion (BLSO) was first recorded in Japan by Goto. The pathogen was considered as a pathovar of Pseudomonas syringae specifically causing disease on onion and Welsh onion, but it has not been taxonomically investigated in detail. In 2012 and 2014, a disease suspected as BLSO re-emerged on onion in Shizuoka and Hyogo Prefectures, Japan, respectively. A pathogenic bacterium isolated from the infected onions was thought to be the BLSO agent after preliminary examinations. Strains isolated from BLSO in 1969, 1986, 1987, 2012 and 2014 were characterized and compared with the causal agent of bacterial blight of leek (P. syringae pv. porri), which causes similar symptoms on Allium plants. The result of rep-PCR distinguished the BLSO agent from P. syringae pv. porri. Multilocus sequence analysis on housekeeping genes and hrp genes encoding the type-III secretion system revealed that the strains of the BLSO agent clustered independently of P. syringae pv. porri. The BLSO agent and P. syringae pv. porri also differed in utilization of erythritol, dl-homoserine, glutaric acid and other bacteriological characteristics and caused different reactions on onion, Welsh onions, chives, shallot, rakkyo, leek, garlic and Chinese chive. Thus, the BLSO agent clearly differs from P. syringae pv. porri and is considered to be a new pathovar of P. syringae. The name P. syringae pv. alliifistulosi is proposed with pathotype strain ICMP3414.     

萝卜软腐病生防菌株Hy11的筛选、鉴定及定殖特性

为探讨银杏内生细菌对萝卜软腐病的防病作用,通过块根接种和温室盆栽试验筛选对萝卜软腐菌Pectobacterium carotovorum subsp.carotovorum具有高效抑制作用的生防菌株,共获得8株拮抗作用较强的内生细菌,其中菌株Hy11抑菌作用明显.对生防菌株Hy11进行了形态观察、生理生化特性测定、16S rDNA和gyrB基因序列分析,并应用绿色荧光蛋白基因标记菌株Hy11,研究该菌株在萝卜体内的定殖动态.结果显示,该菌株对萝卜软腐病具有较好的防效,对萝卜块根和幼苗的防治效果分别为77.9％和66.7％;对萝卜幼苗的促生率达113.28％.经鉴定,菌株Hy11为解淀粉芽胞杆菌Bacillus amyloliquefaciens.标记菌株Hy11-gfp在喷雾接种银杏叶片后0～3 d种群数量呈急剧下降趋势,10d后保持相对稳定;其在萝卜的根、茎和叶中均能够定殖,在根中的定殖数量最高可达1.2×104 CFU/g.     

Bacterial leaf and peduncle soft rot caused byPectobacterium carotovorum on tulips in Konya, Turkey

The etiology of a new soft rot disease of tulips, causing leaf spots, leaf blight, neck and bulb rot in Konya, Turkey, was investigated. This disease occurred in tulip fields grown for seed bulbs of various varieties in 2002. Bacteria were isolated from the lesions on leaf, bud neck and bulbs and the causal bacterium was identified asPectobacterium carotovorum on the basis of biochemical and physiological tests. Cells were Gram-negative, rod-shaped, fermentative, potato-rot positive. Colonies were capable of growth at 37°C. On nutrient agar the colonies were creamy-white. The isolates were non-fluorescent on King’s B medium, positive for acetoin production, gelatin liquefaction, acid-production-from-lactose, and catalase; and negative for gas from glucose, reducing substances from sucrose, and phosphatase activity. Additionally, tests for egg yolk (lecithin), sensitivity to erythromycin, and pigmentation on yeast dextrose carbonate agar were negative; growth on 5% sodium chloride was positive. All the bacterial isolates obtained from the leaf, bud neck and bulbs produced the original symptoms following inoculation to the susceptible tulip variety ‘Gander’. The rate of damage caused by this bacterium was evaluated on several tulip varieties under field and storage conditions. Gander was the most susceptible variety in the field whereas ‘Salmon Parrot’ exhibited the highest rate of bulb rot in storage. Disease severity was lower in 2003 than 2002. http://www.phytoparasitica.org posting May 14, 2006.     

A new pathovar of <Emphasis Type="Italic">Pseudomonas syringae</Emphasis>, pathovar <Emphasis Type="Italic">allii,</Emphasis> isolated from onion plants exhibiting symptoms of blight

Bacterial pathogens of onion (Allium cepa) plants and their undetected presence in seed can cause substantial losses to onion producers. In this study, 23 Pseudomonas syringae strains were isolated from five onion plants and 18 onion seeds. The symptoms on leaves and seed stalks were irregular lesions with necrotic centres and water soaked margins. The aim of the study was to characterize these P. syringae strains using Biolog GN III carbon source utilization, multilocus sequence typing (MLST) based on partial sequences of four housekeeping genes (cts, gapA, gyrB and rpoD), and to determine whether or not the strains were pathogenic on onion (cv. Granex 33), chive (Allium schoenoprasum cv. Grasiue), leek (Allium porrum cv. Giant Italian) and spring onion (Allium fistulosum cv. Salotte) plants. Both Biolog analysis and MLST analysis separated onion strains into two clusters, one supporting the existence of a new pathovar of P. syringae, and the other corresponding to P. syringae pv. porri. Pseudomonas syringae strains belonging to the new pathovar we pathogenic only on onion plants of the Allium spp. tested. The results of this study revealed that bacterial blight of onion in South Africa is caused by two pathovars of P. syringae sensu lato, namely, the newly described pathovar, allii, and P. syringae pv. porri. The symptoms caused by these two pathovars in the field were indistinguishable.