Bacterial leaf blight of sweet pepper (Capsicum annuum) caused by Pseudomonas cichorii in Japan

Sweet peppers (cv. Tosajishi beauty) with leaf blight symptoms were observed in Kochi Prefecture, 2003. Initially, small spots formed on leaves, and later enlarged to brown to dark brown spots, and eventually blighted leaves fell. Several bacteria that caused the same symptoms were isolated and subsequently reisolated. These bacteria were identified as Pseudomonas cichorii on the basis of bacterial characteristics and the 16S rRNA gene sequence. This is the first report of bacterial leaf blight in the sweet pepper in the world.     

Induction of reactive oxygen generation and functional changes in mitochondria and their involvement in the development of bacterial rot in lettuce caused by Pseudomonas cichorii

Pseudomonas cichorii is the major causal agent of bacterial rot disease in lettuce, and apoptosis-like programmed cell death is closely associated with disease development. Depletion of cellular ATP and expression of the alternative oxidase gene was observed in lettuce leaves inoculated with P. cichorii suggesting mitochondrial dysfunction. Cytochemical observation showed production of reactive oxygen species in mitochondria of P. cichorii-inoculated lettuce leaf cells. Release of cytochrome c into the cytosol was also induced by inoculation with the bacterium. Superoxide production was observed in the mitochondrial fraction isolated from P. cichorii-infected leaves much more intense than water-treated leaves. Loss of swelling ability was also observed in the mitochondrial fractions following inoculation with P. cichorii. Intriguingly, inhibitors of the mitochondrial respiratory complex III prevented loss of swelling ability, whereas superoxide generation was scarcely affected by inhibitors of mitochondrial permeability transition in the mitochondrial fractions. Inhibitors of the mitochondrial respiratory complex III and mitochondrial permeability transition delayed not only P. cichorii-induced cell death, but also disease development. In contrast, P. cichorii-induced DNA fragmentation was not inhibited in the presence of either type of inhibitor. The findings suggest that mitochondria may play a crucial role in DNA fragmentation-independent cell death pathway(s).     

First report of bacterial blight of crucifers caused by Pseudomonas cannabina pv. alisalensis in Japan

In October 2010, a bacterial disease produced flecks and spots on leaves of Chinese cabbage, cabbage and Japanese radish in Nagano Prefecture, Japan. The symptoms started on the abaxial surface of leaves as angular, water-soaked flecks of 1–2 mm in diameter with a yellow halo of 3–4 mm width. These flecks then became visible on both leaf surfaces, enlarged and coalesced into large blight lesions. The symptoms were similar to bacterial leaf spot caused by Pseudomonas syringae pv. maculicola. The bacterium isolated from leaf lesions formed a white colony and produced polysaccharides on YP agar. The isolates were identified as P. syringae group by LOPAT tests and the 16S rDNA sequence. Moreover, the results of pathogenicity on cruciferous plants, bacteriological characteristics, rep-PCR and the sequences of rpoD and gyrB showed that the isolates should be identified as P. cannabina pv. alisalensis (recently transferred from P. syringae pv. alisalensis). This is the first report of P. cannabina pv. alisalensis isolated from diseased crucifers in Japan.     

Mechanism of disease development caused by a multihost plant bacterium, Pseudomonas cichorii, and its virulence diversity

Pseudomonas cichorii causes rot on lettuce leaves, distinct from the necrotic spots of infected eggplant leaves. On lettuce leaves, P. cichorii invades intercellular spaces through stomata and grows vigorously, causing rot on the leaves. Surprisingly, P. cichorii does not produce pectate lyase, the most important enzyme for degrading plant cell walls. Alternatively, infection with P. cichorii causes heterochromatin condensation and DNA laddering in lettuce cells, followed by induced cell death, which results in disease symptoms. Thus, apoptotic programmed cell death (PCD) is associated with the symptoms on lettuce leaves. Although PCD in P. cichorii-infected eggplant leaves is also associated with necrotic spots caused by the bacteria, there are differences in the responses of the two hosts. P. cichorii harbors the N-acetyltransferase family gene (pat) and the hrp genes (hrp) encoding a type III secretion system, adjacent to an aldehyde dehydrogenase gene (aldH). The virulence of P. cichorii is hrp-dependent in eggplant, but not in lettuce. Furthermore, hrp, pat and aldH are implicated in the diversity of P. cichorii virulence on susceptible Asteraceae species. The involvement of hrp, aldH and pat in bacterial virulence on the respective species has no relationship with the phylogeny of the plants species. When these results are considered together, P. cichorii has multiple virulence determinants. The involvement of not only hrp but also aldH and pat in P. cichorii virulence arose after species diversification of host plants. Host responses implicated in symptom development have been responsible for the development of virulence determinants of P. cichorii.     

Biology of Pseudomonas cichorii in chrysanthemum1

Since 1982, outbreaks of stem blight caused by Pseudomonas cichorii are sometimes found in greenhouse-grown chrysanthemums in The Netherlands. In this study, 13 Dutch chrysanthemum isolates and, for comparison, six from other origins were biochemically, serologically and pathologically characterized. All isolates were biochemically homogeneous in most of some 40 tests. Different serotypes were observed, which were not host or virulence-correlated. After inoculation into cut and potted chrysanthemum, endive and chicory, P. cichorii isolates were found to be non-host-specific. Isolates showed differences in virulence after inoculation into potted chrysanthemum. For five isolates, disease development at high humidity (85–95% RH, 18°C) was more than 100% greater than at low humidity (55–70% RH, 18°C). Using a selective medium and immunosorbent dilution plating (ISDP), P. cichorii could be isolated from symptomless leaves and soil from nurseries where the disease was observed and from soil of a disease-free nursery. ISDP did not significantly increase the recovery of the pathogen. It was concluded that: (a) P. cichorii is an opportunistic pathogen; (b) epidemic infections of stem blight are due to a combination of high humidity, higher temperatures, high plant density and use of very susceptible cultivars; (c) control measures should concentrate on preventing this combination.     

Bacterial leaf spot of hemp caused by Xanthomonas campestris pv. cannabis in Japan

Bacterial leaf spot disease of hemp was observed in Tochigi Prefecture, Japan in 1982 and characterized by necrotic lesions ca. 1–2 mm diameter on leaves with a yellow halo 2–3 mm wide. In this report, we describe the pathological, physiological and genetic properties of the causal bacterium. Our results indicated that this bacterium is identical with Xanthomonas campestris pv. cannabis reported in Romania.     

A new genomovar of Pseudomonas cichorii, a causal agent of tomato pith necrosis

Recent taxonomic advances, based on biochemical and genotypic processes demonstrate that the plant pathogenic species Pseudomonas cichorii consists of a cluster of closely related genomic groups. Prior to this study, three morphotype groups had been described (C1-C3), all sharing various phenotypic and biochemical characters but partially differing in their DNA content. All entities of the complex could cause disease among a variety of hosts, including lettuce, celery, chrysanthemum and others. In this study, we present the biochemical and molecular characterization of P. cichorii isolates as the causal agent of pith necrosis of tomato plants. A detailed characterization of the genetic variability among strains belonging to P. cichorii was achieved using BOX-PCR and Multi Locus Sequence Analysis utilizing three housekeeping genes (gyrB, rpoD, rpoB). In addition, a number of biochemical and physiological tests were also used for the identification of the tomato P. cichorii isolates. To our knowledge, this is the first complete biochemical, molecular and phylogenetic study of P. cichorii strains isolated from tomato plants affected by pith necrosis disease. Our findings demonstrate the emergence of a new genomovar of P. cichorii, yet another indication for the genetic heterogeneity of the species.     

Pathogenicity and toxigenicity of <Emphasis Type="Italic">Fusarium verticillioides</Emphasis> isolates collected from maize roots,stems and ears in South Africa

Sunflower (Helianthus annuus L.) is an important oilseed crop in South Africa, and is grown in rotation with maize in some parts of North West, Limpopo, Free State, Mpumalanga and Gauteng provinces. Alternaria leaf blight is currently one of the major potential disease threats of sunflower and is capable of causing yield losses in all production regions. Alternaria helianthi was reported as the main cause of Alternaria leaf blight of sunflower in South Africa; however small-spored Alternaria species have been consistently isolated from leaf blight symptoms during recent surveys. The aim of this study was to use morphological and molecular techniques to identify the causal agent(s) of Alternaria blight isolated from South African sunflower production areas. Alternaria helianthi was not recovered from any of the sunflower lesions or seeds, with only Alternaria alternata retrieved from the symptomatic tissue. Molecular identification based on a combined phylogenetic dataset using the partial internal transcribed spacer regions, RNA polymerase second largest subunit, glyceraldehyde-3-phosphate dehydrogenase, translation elongation factor and Alternaria allergen gene regions was done to support the morphological identification based on the three-dimensional sporulation patterns of Alternaria. Furthermore, this study aimed at evaluating the pathogenicity of the recovered Alternaria isolates and their potential as causal agents of Alternaria leaf blight of sunflower. Pathogenicity tests showed that all the Alternaria alternata isolates tested were capable of causing Alternaria leaf blight of sunflower as seen in the field. This is the first report of A. alternata causing leaf blight of sunflower in South Africa.     

First report of spinach leaf spot caused by <Emphasis Type="Italic">Stemphylium</Emphasis> sp. Subgroups C2 and E3 and pathogenicity comparison of the pathogen with related pathogens

Leaf spots on spinach were found in three greenhouses in Hokkaido and Iwate, Japan, in 2011–2012. Three isolates obtained from the lesions were classified into Stemphylium sp. Subgroups C2 and E3, based on morphology and molecular analyses. We compared the three isolates with two reference isolates belonging to Subgroup C2 from Welsh onion and leek in terms of pathogenicity. All five isolates caused leaf spot symptoms on spinach and leaf blight on Welsh onion in inoculation tests. This is the first report of spinach leaf spot caused by Stemphylium sp. Subgroups C2 and E3.     

The spatial structure of spontaneous epidemics of different diseases in a groundnut plot

Spontaneous epidemics of rust, early leaf spot, late leaf spot, andRhizoctonia blight simultaneously developed in a groudnut plot. Geostatistical techniques were used to describe and compare the spatial patterns of epidemics.Rhizoctonia blight exhibited a strong aggregative structure, contrasting with leaf spots and rust. The latter disease developed a general epidemic, in combination with local intensification. A strong negative interaction between rust and early leaf spot, and a close correspondence between rust intensification andRhizoctonia blight development were indicated.     

Coffee bacterial diseases: a plethora of scientific opportunities

Coffee is a very important crop for several tropical countries across different continents. The diseases bacterial halo blight (BHB), bacterial leaf spot (BLS), bacterial leaf blight (BLB) and coffee leaf scorch (CLS), caused by the bacterial pathogens Pseudomonas syringae pv. garcae (Psgc), P. syringae pv. tabaci (Psta), Pseudomonas cichorii (Pch) and Xylella fastidiosa subsp. pauca (Xfp), respectively, cause significant reductions in coffee production, although other minor bacterial diseases have also been reported in some countries. Little research progress has been made on aspects that are relevant for control and management of these diseases. In all cases, there is an urgent need to develop rapid and more reliable methods for early detection of the pathogens in order to minimize their negative impact on coffee production. Because of the high rate of intra- and intersubspecific recombination occurring in X. fastidiosa, a permanent revision of the detection methods is necessary. Greater efforts should be made to understand the genetic and virulence diversity of Psgc, Psta and Pch populations. Early studies reported the identification of potential sources of resistance against Psgc and Psta, but, to date, no resistance gene has been isolated. Little effort has been made to understand the biology and molecular mechanisms underlying the interaction between Coffea spp. and these pathogenic bacteria. This review discusses the recent progress on the molecular mechanisms used by these bacteria to cause diseases on other plant species, in order to provide a guideline for the establishment of future research programmes.     

The N-acetyltransferase gene-implicated iron acquisition contributes to host specificity of Pseudomonas cichorii strain SPC9018 and its virulence

A pathogenicity island within the genome of a multi-host plant bacterium, Pseudomonas cichorii strain SPC9018, comprises the hrp genes encoding a type III secretion system and the pat gene encoding an N-acetyltransferase proposed to play a role in virulence. However, the function of the N-acetyltransferase remains poorly characterized. Interestingly, limiting the iron condition using a phytosiderophore, mugineic acid, resulted in reduced virulence of strain SPC9018 on respective host plants, including eggplant, similar to the reduced virulence observed with a pat gene-deletion mutant. Spectroscopic analyses showed that the pat deletion reduced the concentration of pyoverdine, which is the main siderophore produced by strain SPC9018, leading to a reduction in pyoverdine-mediated iron acquisition. Furthermore, the pat gene deletion mutant showed enhanced expression of the fecA, pvdL, and pvdR genes, whose expression is induced under deficient siderophore-mediated iron uptake. The pat-deletion mutant showed a hyper-swarming phenotype, and the addition of iron decreased this swarming motility. The pat deletion also reduced the adhesion ability of the bacteria, similar to the effect of iron-limited conditions. Furthermore, deletion of the pat gene enhanced expression of the hrp genes. These findings suggested that the pat gene encoding the N-acetyltransferase may be implicated in iron acquisition, contributing to host specificity of P. cichorii strain SPC9018 and its virulence.     

观赏百合叶枯病症状类型与病原菌鉴定

引起甘肃省百合叶枯病的主要致病菌为椭圆葡萄孢[Botrytis elliptica(Berk.)Cooker],分离率为70.5%;其次是灰葡萄孢(Botrytis cinerea Peers),分离率为23.0%。该病原菌在不同品种百合叶片上造成的症状有4种类型。不同症状类型病斑分离的病原菌种类不同,其中紫缘黄褐斑型、褐色环纹型和黄缘褐斑型主要致病菌为椭圆葡萄孢,平均分离率为82.5%;叶缘干枯型的主要致病菌为灰葡萄孢,分离率达93.7%。温度为15℃时,易产生菌核;菌核萌发最适温度为15~20℃。     

Leaf and stem blight ofEuphorbia geniculata incited byBipolaris zeicola

Recently leaf and stem blight disease was observed onEuphorbia geniculata Orteg. The pathogen was isolated in pure culture and identified asCochliobolus carbonum Nelson (anamorph:Bipolaris zeicola (Stout) Shoem. =Helminthosporium carbonum Ullstrup). This is the first record of this fungus causing leaf and stem blight disease onE. geniculata. In a greenhouse study, none of 19 other plant species tested showed pathogenic reactions. The specific host range and highly virulent nature ofB. zeicola onE. geniculata indicated that this pathogen has potential for use as a biocontrol agent forE. geniculata.     

Identification of Rhizoctonia solani AG1-IB as a causal agent of leaf blight in Cynanchum paniculatum in China

A severe disease causing leaf blight of Cynanchum paniculatum was observed in China. From the diseased plants, 24 fungal isolates were obtained. Morphological observations and nuclear conditions of all the isolates indicated characteristics of Rhizoctonia solani. The ribosomal DNA internal transcribed spacer sequences of the isolates showed more than 99 % sequence homology with published sequences of R. solani anastomosis group 1 subgroup IB (AG1-IB). All tested isolates were pathogenic and showed significant symptoms as observed in the fields. This is the first report of leaf blight of C. paniculatum caused by R. solani AG1-IB worldwide.     

Shoot Blight and Leaf Spot of Blueberry Anthracnose Caused by <Emphasis Type="Italic">Colletotrichum acutatum</Emphasis>

Shoot blight and leaf spots were found on highbush blueberry trees in Tsukuba, Ibaraki, in 1999. The causal fungus was identified morphologically as Colletotrichum acutatum Simmonds ex Simmonds. This is the first report of blueberry anthracnose caused by C. acutatum in Japan. Received 16 November 2001/ Accepted in revised form 22 March 2002     

<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.     

Gray mold of yacon and sunflower caused by Botrytis cinerea

Severe wilt and blight of entire plants of yacon (Smallanthus sonchifolius) grafts on sunflower (Helianthus annuus) were found in greenhouses in Kagawa Prefecture in the southwest region of Japan from April to May between 1997 and 1999. A mitosporic fungus, isolated repeatedly from the diseased plants and identified as Botrytis cinerea, was demonstrated to be virulent to both yacon and sunflower. The new disease on yacon was named gray mold of yacon. The disease on sunflower, gray mold of sunflower, is new to Japan.     

Botrytis blight of Taiwanese toad lily caused by Botrytis elliptica (Berkeley) Cooke

In June 1998, leaf spots caused by Botrytis elliptica (Berkeley) Cooke were found on Taiwanese toad lily (Tricyrtis formosana Bak.) in Kanagawa Prefecture, Japan. This is the first report on Botrytis blight of T. formosana caused by B. elliptica.     

Phytophthora infestans: a review of past and current studies on potato late blight

Phytophthora infestans is the causal agent of potato late blight. Genotypes of Japanese populations of P. infestans have been classified as US-1, JP-1, JP-2, JP-3, and JP-4 based on analyses of DNA polymorphisms. These populations may have been introduced to Japan by the migration of P. infestans from other countries and by domestic changes produced through sexual and asexual propagation. Resistance to late blight has been an ongoing desire of potato farmers in Japan and elsewhere. Recurrent backcrossing of Solanum demissum to varieties of S. tuberosum has been used to transfer late blight resistance. Many varieties carry the R1 gene, whereas others carry R2, R3, and/or R4. However, R genes provided only transient resistance to late blight. New races rapidly overcome R-gene-mediated resistance. The R genes of potato generally encode receptors that recognize secretory effector (Avr) proteins produced by P. infestans. These effector proteins induce robust resistance in potato varieties containing R genes, while they suppress resistance in potato varieties lacking R genes. Conserved molecules from Phytophthora species such as fatty acids, glucans, and elicitins also act as elicitors in Solanaceae species. These P. infestans-derived elicitors induce defensive reactions, including the accumulation of phytoalexins and hypersensitive cell death. A future challenge will be to combine our accumulated knowledge with that from other scientific fields to develop a disease management approach for late blight.