Showing papers in "Journal of General Plant Pathology in 2013"
TL;DR: The task is to maintain the effectiveness and diversity of the present modes of action for fungicides and implement countermeasures against the development of fungicide resistance.
Abstract: As the world population increases, we also need to increase food production. Chemical control has been critical in preventing losses due to plant diseases, especially with the development of numerous specific-action fungicides since the 1960s. In Japan, a host-defense inducer has been used to control rice blast since the 1970s without any problems with resistance development in the pathogen. Leaf blast has been controlled using a labor-saving method such as the one-shot application of a granular mixture of fungicide and insecticide to nursery boxes, which became mainstream in the 2000s. However, the need for many choices of fungicides that have several modes of action was demonstrated by the development of resistance to cytalone dehydratase inhibitors. In Europe, many pathogens have threatened cereals since the great increase in cereal production in 1970s, creating a large market for broad-spectrum fungicides. In Brazil, Phakopsora pachyrhizi was distributed to large soybean acreages during 2000s, and the outbreak of soybean rust resulted in a large increase in fungicide use. While the importance of chemical control is recognized, fungicide resistance is an avoidable problem; published guidelines on countermeasure and manuals on testing sensitivity to fungicides are available. Since chemical regulations have become stricter, new fungicides are less likely to be developed. Our task is to maintain the effectiveness and diversity of the present modes of action for fungicides and implement countermeasures against the development of fungicide resistance.
67 citations
TL;DR: This review considers the discoveries made during 60 years of study on C. orbiculare and focuses on advances made in the last two decades, which have provided a basis for the molecular analysis not only of fungal morphogenesis, but also of plant–microbe interactions, including plant immunity to adapted and nonadapted Colletotrichum fungi.
Abstract: Colletotrichum orbiculare (syn C lagenarium) is the causal agent of anthracnose disease on cucurbit plants This fungus forms dome-shaped, melanized appressoria as a host invasion structure Strain 104-T (MAFF240422) of C orbiculare, which was originally isolated from a cucumber plant in 1951 by Dr Yasumori, Kyoto University, has proven to be an excellent experimental model for the study of fungal pathogenesis and morphogenesis because of its stable pathogenicity and synchronous infection-related morphogenesis This review considers the discoveries made during 60 years of study on C orbiculare In particular, we focus on advances made in the last two decades, which have provided a basis for the molecular analysis not only of fungal morphogenesis, but also of plant–microbe interactions, including plant immunity to adapted and nonadapted Colletotrichum fungi This substantial body of innovative research was originated by the Phytopathological Society of Japan and represents a major contribution to the international research communities working on plant pathology, plant–microbe interactions, and fungal molecular genetics This review deals with the past achievements and future prospects in the study of Colletotrichum biology, focusing on the molecular genetics of C orbiculare with regard to four aspects: (1) metabolic and functional development of infection structures, (2) signaling pathways required for fungal pathogenesis, (3) pathogen-associated molecular patterns (PAMPs) and host basal resistance, and (4) establishment of host specificity
60 citations
TL;DR: It is demonstrated that P. pachyrhizi populations from South America vary geographically and temporally in pathogenicity and that the known Rpp genes other than Rpp1 in PI 587880A and Rpp5 have been less effective against recent pathogen populations in the countries studied.
Abstract: Phakopsora pachyrhizi, the cause of soybean rust, is an economically important pathogen of soybean in South America. Understanding the pathogenicity of indigenous fungal populations is useful for identifying resistant plant genotypes and targeting effective cultivars against certain populations. Fifty-nine rust populations from Argentina, Brazil, and Paraguay were evaluated for pathogenicity in three cropping seasons, 2007/2008–2009/2010, using 16 soybean differentials. Only two pairs of P. pachyrhizi populations displayed identical pathogenicity profiles, indicating substantial pathogenic variation in the rust populations. Comparative analysis of 59 South American and five Japanese samples revealed that pathogenic differences were not only detected within South America but also distinct between the P. pachyrhizi populations from South America and Japan. In addition, seasonal changes in rust pathogenicity were detected during the sampling period. The differentials containing resistance genes (Rpp: resistance to P. pachyrhizi) Rpp1, Rpp2, Rpp3, and Rpp4, except for Plant Introduction (PI) 587880A, displayed a resistant reaction to only 1.8–14, 24–28, 22, and 36 % of South American P. pachyrhizi populations, respectively. In contrast, PI 587880A (Rpp1), Shiranui (Rpp5), and 3 Rpp-unknown differentials (PI 587855, PI 587905, and PI 594767A) showed a resistant reaction to 78–96 % of all populations. This study demonstrated that P. pachyrhizi populations from South America vary geographically and temporally in pathogenicity and that the known Rpp genes other than Rpp1 in PI 587880A and Rpp5 have been less effective against recent pathogen populations in the countries studied.
60 citations
TL;DR: This work has attempted to characterize pathogenicity, the ability of a pathogen to cause disease, using the phytopathogenic bacterium Pseudomonas syringae as a representative pathogen.
Abstract: In 1994, Oku reported that plant pathogens, mainly fungal pathogens, require three essential abilities to infect plants: to enter plants, to overcome host resistance, and to evoke disease. Because the infectious process of phytopathogenic bacteria differs from that of fungal pathogens, we have attempted to characterize pathogenicity, the ability of a pathogen to cause disease, using the phytopathogenic bacterium Pseudomonas syringae as a representative pathogen. To establish infection and incite disease development, bacteria first have to enter a plant. This process requires flagella- and type IV pili-mediated motility, and active taxis is probably necessary for effective infection. After bacteria enter a plant’s apoplastic spaces, they need to overcome host plant resistance. To do this, they secrete a wide variety of hypersensitive response and pathogenicity (Hrp) effector proteins into the plant cytoplasm to interfere with pathogen/microbe-associated molecular pattern- and effector-triggered immunity, produce phytohormones and/or phytotoxins to suppress plant defense responses and extracellular polysaccharides to prevent access by antibiotics and to chelate Ca2+, and activate the multidrug resistance efflux pump to extrude antimicrobial compounds for successful colonization. Furthermore, to evoke disease, bacteria produce toxins and Hrp effectors that compromise a plant’s homeostasis and injure plant cells. The expression of these virulence factors depends on the infection processes and environmental conditions. Thus, the expression and function of virulence factors interact with each other, creating complex networks in the regulation of bacterial virulence-related genes.
58 citations
TL;DR: For six major virus diseases, this work addresses their geographical distribution, diversity, and genetic resistance, and identifies three species of plasmodiophorids that are recognized as vectors.
Abstract: About 20 species of viruses belonging to five genera, Benyvirus, Furovirus, Pecluvirus, Pomovirus and Bymovirus, are known to be transmitted by plasmodiophorids. These viruses have all positive-sense, single-stranded RNA genomes that consist of two to five RNA components. Three species of plasmodiophorids are recognized as vectors: Polymyxa graminis, P. betae, and Spongospora subterranea. The viruses can survive in soil within the long-lived resting spores of the vector. There are biological and genetic variations in both virus and vector species. Many of the viruses are causal agents of important diseases in major crops such as rice, wheat, barley, rye, sugar beet, potato, and groundnut. Control is dependent on the development of resistant cultivars. During the last half century, several virus diseases have rapidly spread worldwide. For six major virus diseases, we address their geographical distribution, diversity, and genetic resistance.
44 citations
TL;DR: A virus-like dsRNA of about 23 kbp was detected in gentian plants showing Kobu-sho syndrome including stunting, shortened internodes, and tumors on stems, nodes and roots and it was protected from externally added RNase, suggesting that the ds RNA is encapsidated.
Abstract: A virus-like dsRNA of about 23 kbp was detected in gentian plants showing Kobu-sho syndrome including stunting, shortened internodes, and tumors on stems, nodes and roots. Nucleotide sequence analysis has suggested that this dsRNA is related to Pestivirus species but not to any other plant viruses. It was protected from externally added RNase, suggesting that the dsRNA is encapsidated. The dsRNA was co-extracted in a crude homogenate of glutaraldehyde-fixed tissue with the virus-like particles that have been associated previously with Kobu-sho syndrome in gentian (Usugi et al. Jpn J Phytopathol 76:21–24, 2010). The RNA sequence was detected in more than 99 % of Kobu-sho gentian individuals but in less than 20 % of apparently healthy gentian individuals from fields affected with Kobu-sho. Thus, we propose naming the virus Gentian Kobu-sho-associated virus.
37 citations
TL;DR: When nine potato varieties were inoculated with several Rs strains, phylotype IV strains were highly virulent on the breeding lines that are regarded as resistant to phylotype I strains.
Abstract: Ralstonia solanacearum (Rs) strains in phylotypes I and IV isolated from potato in Japan were investigated for pathogenicity on potato, tomato, eggplant, Solanum
integrifolium, tobacco, groundnut, and pumpkin. The strains were divided into 17 types based on differences in their pathogenicity on the tested plants. Particularly, the pathogenicity of most phylotype I strains on eggplant was distinctly different from that of the phylotype IV strains. When nine potato varieties (included two breeding lines) were inoculated with several Rs strains, phylotype IV strains were highly virulent on the breeding lines that are regarded as resistant to phylotype I strains.
24 citations
TL;DR: It is shown that a begomovirus, Tomato yellow leaf curl virus (TYLCV), can enter midgut epithelial cells of the vector whitefly B. tabaci but not those of a nonvector whitefly, Trialeurodes vaporariorum, belonging to the same family.
Abstract: Begomoviruses are transmitted by a single species of vector insect, the whitefly Bemisia tabaci, in a circulative manner. However, the mechanisms of this strict vector specificity have not been clarified. By immunoelectron microscopy, we showed that a begomovirus, Tomato yellow leaf curl virus (TYLCV), can enter midgut epithelial cells of the vector whitefly B. tabaci but not those of a nonvector whitefly, Trialeurodes vaporariorum, belonging to the same family. In midgut epithelial cells of viruliferous B. tabaci, the virus was localized in vesicle-like structures, suggesting endocytosis as an entry mechanism. These structures were also observed in midgut cells of nonviruliferous B. tabaci that had fed on healthy plants and in those of the nonvector T. vaporariorum that had fed on virus-infected plants. Vesicles containing TYLCV particles were observed most frequently in cells in the anterior part of the descending midgut, suggesting that this is the major entry site. These results clearly demonstrated that the virus-containing vector and nonvector whiteflies differ in the cellular localization of the virus and strongly suggest that a critical step in determining the vector insect specificity of begomoviruses is the entry of the viruses into midgut epithelial cells.
24 citations
TL;DR: Putative ancestral features of the powdery mildews are described as follows: in teleomorphs, large-sized chasmothecia, containing many 8-spored asci, had many appendages with uncinate-circinate apices, arising around the supraequatorial part of chasmotivecia.
Abstract: Powdery mildew fungi, comprising 16 genera and ca. 900 species, are exclusively obligate biotrophs of plants. Although several publications have addressed the phylogeny and evolution of powdery mildews based on morphology and host relationships, this review focuses on the evolution of several phenotypic characters based on molecular phylogeny: (1) morphology of appendages; (2) mycelium, ectoparasitic or endoparasitic; (3) number of asci per chasmothecium (fruiting body of powdery mildews), e.g., one to several; (4) conidiogenesis, conidia catenescent (i.e., maturing in chains: Euoidium-type) or maturing one at a time (Pseudoidium-type). Putative ancestral features of the powdery mildews are described as follows. In teleomorphs, large-sized chasmothecia, containing many 8-spored asci, had many appendages with uncinate-circinate apices, arising around the supraequatorial part of chasmothecia. In anamorphs, conidia were produced in chains (Euoidium-type) without distinct fibrosin bodies. Parasitism was ectoparasitic.
23 citations
TL;DR: Results suggested that FocSIX4 is involved in virulence, but not in avirulence, in the cabbage yellows fungus.
Abstract: Six4, a small protein secreted by Fusarium oxysporum f. sp. lycopersici (Fol) in tomato xylem sap during infection, triggers Fol race 1-specific resistance (I) in tomato. SIX4 is regarded as an avirulence gene. Although SIX4 is considered unique to Fol race 1, we detected this gene in the cabbage yellows fungus F. oxysporum f. sp. conglutinans (Foc) by PCR. Because the genes from Foc and SIX4 in Fol were >99 % identical at the nucleotide level, the Foc gene was designated FocSIX4. The expression of FocSIX4 was detected by RT-PCR in stems and roots of cabbage 8 days after infection with Foc. In contrast with Fol, disruption of FocSIX4 in Foc did not increase virulence to Foc-resistant cabbage cvs. Shutoku-SP and Koikaze. On the contrary, the disruptants had reduced virulence not only on Foc-resistant cultivars but also on Foc-susceptible cv. Shikidori. These results suggested that FocSIX4 is involved in virulence, but not in avirulence, in the cabbage yellows fungus.
22 citations
TL;DR: Internal transcribed spacer analysis showed all isolates are 90–100 % similar to each other, indicating genetic similarity among different A. brassicae isolates that vary pathogenically.
Abstract: Cauliflower (Brassica oleracea L. var. botrytis) and mustard [Brassica juncea (L.) Czern] are important cruciferous crops facing serious yield and quality loss in India from dark leaf spot disease caused by Alternaria brassicae (Berk.) Sacc. Genetic variation among 32 pathogenic A. brassicae isolates from both crops was analyzed with random amplified polymorphic DNA and inter-simple sequence repeat primers in which the mean similarity coefficient was found to be 0.73 and 0.84, respectively. Further internal transcribed spacer analysis showed all isolates are 90–100 % similar to each other, indicating genetic similarity among different A. brassicae isolates that vary pathogenically.
TL;DR: A leaf spot on oil palm, caused by Pestalotiopsis theae, was found in a plantation of Elaeis guineensis for the first time in the world in Chiang Mai Province, Thailand and its pathogenicity was confirmed.
Abstract: A leaf spot on oil palm, caused by Pestalotiopsis theae, was found in a plantation of Elaeis guineensis for the first time in the world in Chiang Mai Province, Thailand. The fungus was isolated from lesions on leaves, and its pathogenicity was confirmed. Pathogenicity tests showed that P. theae could infect E. guineensis, which developed the same symptoms after inoculation as those observed naturally in the field. The fungus was identified based on morphological characteristics and confirmed using comparisons of DNA sequences of internal transcribed spacer (ITS)1, ITS2 and 5.8S rDNA. This report is the first on oil palm leaf spot disease caused by P. theae.
TL;DR: When the multiplex PCR was applied to naturally infested soils, the expected species were reliably identified, suggesting that the method is suitable for the detection of the three Pythium pathogens in environmental samples.
Abstract: The objective of this study was to develop a multiplex PCR detection method for the high-temperature-growing pathogens Pythium aphanidermatum, P. helicoides and P. myriotylum. Species-specific primer pairs were designed that targeted the rDNA ITS regions. The multiplex PCR was constructed with a universal primer pair for eukaryotes directed at the 18S rDNA as a positive control, in addition to the three species-specific primer pairs. When the multiplex PCR was applied to naturally infested soils, the expected species were reliably identified, suggesting that the method is suitable for the detection of the three Pythium pathogens in environmental samples.
TL;DR: This is the first report of white leaf rot on Chinese chive caused by R. solani AG-2-1, and it appears that symptoms and the time of year that the disease occurs also apparently differ for the two pathogens.
Abstract: Delayed sprouting and white rot of leaf tips were found on Chinese chives in a greenhouse in Hokkaido, Japan, in the spring of 2006 and 2007 The causal fungus was identified as Rhizoctonia solani anastomosis group (AG)-2-1 and discriminated from the leaf rot pathogen R solani AG-4 HG-I in terms of pathogenicity Symptoms and the time of year that the disease occurs also apparently differ for the two pathogens This is the first report of white leaf rot on Chinese chive caused by R solani AG-2-1
TL;DR: Analysis indicated that a culture supernatant of V. dahliae induced lesion formation in tobacco leaves; de novo protein synthesis not active gene expression was required for this induction, and Lesion formation was dependent on the age of leaves, but neither the known ROS burst nor the ubiquitin/26S proteasome system are prerequisites.
Abstract: Verticillium dahliae is one of the most destructive soil-borne fungal pathogens that cause vascular wilt diseases in a wide range of important crop plants, including cotton. However, the mechanisms used by this pathogen to infect cotton have not been fully elucidated. In the present study, we first investigated changes in protein abundance during the initial interaction between cotton roots and V. dahliae. Among the proteins that were upregulated upon infection, some were related to reactive oxygen species (ROS); among those downregulated upon infection were proteins involved in normal metabolism or cell structure. Further experiments confirmed that a sudden release of ROS and cell death accompany V. dahliae infection in the cotton vasculature. Further analysis indicated that a culture supernatant of V. dahliae induced lesion formation in tobacco leaves; de novo protein synthesis not active gene expression was required for this induction. Lesion formation was dependent on the age of leaves, but neither the known ROS burst nor the ubiquitin/26S proteasome system are prerequisites.
TL;DR: The result implies an interesting genetic relationship among Williams’ races, among pathotypes determined using CR cultivars of Chinese cabbage and among populations from crops and C. flexuosa.
Abstract: Clubroot disease, caused by Plasmodiophora brassicae Woronin, affects various cruciferous crops. Variations in pathogenicity and virulence are present among field populations of P. brassicae. Many races (pathotypes) have been reported in Japan as well as in other countries using various differential systems. Populations can be classified into four pathotypes using two clubroot-resistant (CR) cultivars of Chinese cabbage as differential hosts in Japan. However, it was recently indicated that each population is often heterogenic and composed of multiple genotypes (races or pathotypes). Breakdown in CR cultivars of Chinese cabbage is a problem in some areas of Japan and may contribute to the selective propagation of minor pathogenic genotypes on the CR cultivars. Clubroot has also been recorded on five species of cruciferous weeds in Japan. In particular, clubroot of Cardamine flexuosa is widely distributed in Japan. Some populations of C. flexuosa are often moderately pathogenic on Chinese cabbage and turnip. Therefore, the epidemiological relationship between clubroot of cruciferous crops and that of the weed has been noted but not thoroughly clarified. The relationship between pathogenic and genetic variations has also been examined among populations from cruciferous crops and weeds in Japan. The result implies an interesting genetic relationship among Williams’ races, among pathotypes determined using CR cultivars of Chinese cabbage and among populations from crops and C. flexuosa. This review includes an introduction of the status of studies on pathogenic and genetic diversity in P. brassicae from Japan.
TL;DR: It is concluded that the AsA derivatives and DHA can significantly reduce viral infection and accumulation and that those compounds can be developed as a practical antiviral agent in the future.
Abstract: Plants may activate posttranscriptional gene silencing (PTGS) as an immunity system when they are infected with viruses. Viruses may in turn interfere with this system by producing RNA silencing suppressor (RSS) proteins; most RSSs bind to viral small interfering RNAs (siRNAs). We previously reported that ascorbic acid (AsA) has the ability to interfere with the binding between viral siRNAs and viral RSSs in vitro. We thus expected that AsA-treated plants would show some tolerance to virus infection because the host PTGS will be strengthened by AsA. Brassica rapa subsp. rapa was inoculated with Turnip mosaic virus and treated with the AsA derivatives, l(+)-ascorbic acid 2-sulfate disodium salt dihydrate (AsA–SO4), l(+)-ascorbyl palmitate (AsA–Pal) and dehydroascorbic acid (DHA) at 1 h postinoculation. The number of infection sites on inoculated leaves decreased by around 40 % after AsA–SO4 and AsA–Pal treatments and by 80 % after DHA treatment compared with the untreated control. As evidenced by an enzyme-linked immunosorbent assay, viral accumulation was significantly reduced after regular sprays with the AsA derivatives and DHA. In a detached leaf assay, AsA clearly functioned as a viral inhibitor in cells. Additionally, we confirmed that DHA also worked in the silencing pathway because its antiviral effect was not observed in the silencing-defective double mutant dcl2/dcl4 of Arabidopsis thaliana. On the basis of these results, we concluded that the AsA derivatives and DHA can significantly reduce viral infection and accumulation and that we can develop those compounds as a practical antiviral agent in the future.
TL;DR: A viroid was detected for the first time in symptomless petunia plants (Petunia spp.) and identified as Tomato chlorotic dwarf viroid (TCDVd) based on an analysis of the complete genomic sequence.
Abstract: A viroid was detected for the first time in symptomless petunia plants (Petunia spp.) and identified as Tomato chlorotic dwarf viroid (TCDVd) based on an analysis of the complete genomic sequence. These petunia plants are a likely source of inoculum for tomato or potato plants because TCDVd induces severe symptoms on these plants. The genomic sequence of this petunia isolate from Japan shared 100 % identity with petunia isolates from the Netherlands and United Kingdom and a tomato isolate from Japan. Phylogenetic analysis showed that all petunia isolates and the tomato isolate from Japan formed a monophyletic clade.
TL;DR: The fungus that was frequently isolated from the damaged fruits was identified as Cladosporium cladosporioides, and inoculation of fruits with the fungus caused the same symptoms, and the fungus was reisolated from the diseased fruits.
Abstract: In June 2006, a large number of small black spots containing a branching network of black hyphae developed on shipped Satsuma mandarin fruits grown in greenhouses, which markedly decreased their commercial value. The fungus that was frequently isolated from the damaged fruits was identified as Cladosporium cladosporioides. Inoculation of fruits with the fungus caused the same symptoms, and the fungus was reisolated from the diseased fruits. The disease caused by this fungus has not been previously documented in citrus fruits; we name this new disease “sooty spot” on the basis of its symptoms.
TL;DR: It is conceivable that M. pinodes has evolved a strategy to condition susceptibility by manipulating the physiology of host cells, in particular JA-regulated cellular process(es), to promote disease development in pea.
Abstract: Using a recently developed model pathosystem involving Medicago truncatula and Mycosphaerella pinodes, causal agent of Mycosphaerella blight on pea to understand host molecular response to a fungal suppressor, we applied the suppressor to leaves of M. truncatula and identified 151 nonredundant cDNA fragments as newly expressed genes. These included genes encoding lipoxygenase (LOX) and enoyl-CoA hydratase, which are presumably involved in jasmonic acid (JA) synthesis. Potential genes encoding plastidic enzymes, including allene oxide synthase (AOS) and allene oxide cyclase (AOC), and other peroxisomal enzymes involved in β-oxidation were predicted from the Medicago Gene Index EST database and tested for altered expression by semiquantitative RT-PCR. The coordinated expression of genes encoding both plastidic and peroxisomal enzymes showed that the suppressor likely conditions certain cellular process(es) through the JA synthesis in M. truncatula. To explore the role of JA or JA-regulated cellular process(es) in conditioning susceptibility, we used an Apple latent spherical virus (ALSV)-based virus-induced gene silencing (VIGS) technology to silence pea genes including LOX, AOS, AOC and 12-oxo-phytodienoic acid reductase (OPR). In LOX-, AOS-, AOC- or OPR-silenced pea plants, disease development induced by M. pinodes was remarkably reduced. Similarly, silencing of mRNA for LOX, AOS, AOC or OPR reduced the sensitivity to a phytotoxin, coronatine, which is believed to act through a JA-dependent process. On the basis of these results, it is conceivable that M. pinodes has evolved a strategy to condition susceptibility by manipulating the physiology of host cells, in particular JA-regulated cellular process(es), to promote disease development in pea.
TL;DR: The results suggest that using the combination of the genes EF1-α1 and RPB2 is highly reliable for molecular characterization of Trichoderma species.
Abstract: Twenty-one isolates of Trichoderma spp. were collected from eight states in Colombia and characterized based on the 5′ end of the translation elongation factor-1α (EF1-α1) gene and RNA polymerase II gene encoding the second largest protein subunit (RPB2) by using mixed primers. Seven species of soil-dwelling Trichoderma were found: T. atroviride, T. koningiopsis, T. asperellum, T. spirale, T. harzianum, T. brevicompactum and T. longibrachiatum. Species identifications based on the EF1-α1 gene were consistent with those obtained from the RPB2 gene. Phylogenetic analyses with high bootstrap values supported the validity of the identification of all isolates. These results suggest that using the combination of the genes EF1-α1 and RPB2 is highly reliable for molecular characterization of Trichoderma species. Trichoderma asperellum Th034, T. atroviride Th002 and T. harzianum Th203 prevented germination of more than 70 % of sclerotia of Sclerotinia sclerotiorum in bioassay tests and are promising biological control agents. No relationship between mycelium growth rate and parasitism level was found.
TL;DR: The four topics and the present state and perspectives concerning biological control against plant diseases: the use of plant probiotics, i.e., plantgrowth-promoting fungi (PGPF) and endophytic bacteria; metagenomic analysis, for clues to the mechanisms of disease suppressiveness; and transgenerational systemic acquired resistance (SAR).
Abstract: The aim of research on biological control is to reduce the inoculum density and the activity of the pathogens that cause disease (Baker and Cook 1974). A primary focus is the search for naturally occurring harmless and/or beneficial microorganisms and subsequent analysis of their biocontrol potential. That focus simply reflects the slogan ‘‘From field to the lab and back again’’ of the XII Meeting of IOBC-WRPS (International Organization for Biological and Integrated Control-West Palaearctic Regional Section). Growing concerns about environmental health and safety have led to substantial regulatory changes in crop management in the past several years. Therefore, interest in biological control research continues reflecting the desire of multiple constituencies to develop sustainable methods for controlling plant disease. Reducing the use of fertilizers and fungicides in agricultural production is necessary to help maintain ecosystems and to develop sustainable agriculture. The use of both biofertilizers and biocontrol systems can have minimal effects on the environment, and such strategies have been widely researched. In soil, numerous microorganisms coexist in association with plant roots. Some microorganisms live specifically in the rhizosphere or on/in plant roots and can affect the performance of the plant and the structure of the microbial community in many ways. In particular, the microfloral community around the plant root surface, where various substances are secreted, is unique. Most of the microorganisms around the plant root surface have a role in decomposing organic matter, and some may suppress deleterious microorganisms and promote plant growth. In this paper, I discuss the four topics and the present state and perspectives concerning biological control against plant diseases: the use of plant probiotics, i.e., (1) plantgrowth-promoting fungi (PGPF) and (2) endophytic bacteria; (3) metagenomic analysis, for clues to the mechanisms of disease suppressiveness; and (4) transgenerational systemic acquired resistance (SAR). Of these, I will especially focus on PGPF and talk comprehensively on our biological control work using PGPF.
TL;DR: A transcriptional study of a salicylic acid (SA)-regulated gene encoding pathogenesis-related protein 10-1 indicated that the suppressor likely interferes with the signal transduction process leading to inducible defenses in M. truncatula, rendering the host tissues susceptible to unrelated nonpathogenic fungi.
Abstract: A model pathosystem involving Mycosphaerella pinodes, causal agent of Mycosphaerella blight on pea and barrel medic(k) Medicago truncatula has been developed. Nineteen M. truncatula ecotypes were evaluated for disease susceptibility to M. pinodes strain OMP-1, using detached leaves inoculated with a pycnospore suspension. Inoculation of ecotype R108-1 with the pycnospores allowed direct penetration into the host’s epidermal cells, eventually causing leaf spots. Since pycnidia formed abundantly in infected tissues by 3 days post inoculation, M. pinodes is considered to have completed its infection cycle as on a natural host plant. Expression of phenylalanine ammonia-lyase (PAL)-, chalcone synthase (CHS)- and isoflavone reductase (IFR) mRNAs as well as subsequent accumulation of a major phytoalexin, medicarpin, was induced in ecotype R108-1 with an elicitor preparation from M. pinodes, whereas this phytoalexin response was markedly attenuated by supprescins from the same fungus. A transcriptional study of a salicylic acid (SA)-regulated gene encoding pathogenesis-related protein 10-1 (PR10-1) indicated that the suppressor likely interferes with the signal transduction process leading to inducible defenses in M. truncatula. Indeed, the suppressor rendered the host tissues (ecotype R108-1) susceptible to unrelated nonpathogenic fungi, probably through targeting ATPase activity of the host cells. Accordingly, the resistant and susceptible response of pea can be recapitulated in M. truncatula. This model pathosystem thus will allow us to verify the molecular basis underlying the fungal suppressor-mediated plant susceptibility.
TL;DR: 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.
Abstract: 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.
TL;DR: Pseudomonas cichorii causes rot on lettuce leaves, distinct from the necrotic spots of infected eggplant leaves, and apoptotic programmed cell death (PCD) is associated with the symptoms on lettuce Leaves.
Abstract: 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.
TL;DR: The results suggest that flagellin glycosylation is ubiquitous in most phytopathogenic bacteria and that flagescence is required for virulence in Xcc.
Abstract: Glycosylation of flagellin is known to be involved in filament stabilization, motility, and virulence in Pseudomonas
syringae. Here we investigated flagellin glycosylation in other phytopathogenic bacteria. Analyses of deduced amino acid sequences, glycostaining, and molecular masses of purified flagellins revealed that flagellins from all phytopathogenic bacteria investigated were glycosylated. Furthermore, the flagellin in a glycosylation-defective mutant of Xanthomonas campestris pv. campestris (Xcc) had a reduced molecular mass, and motility and virulence of the mutant toward host leaves decreased. These results suggest that flagellin glycosylation is ubiquitous in most phytopathogenic bacteria and that flagellin glycosylation is required for virulence in Xcc.
TL;DR: DGA01 and SBC was the best combination for crown rot control, with an efficacy similar to synthetic fungicides, and maintained the overall quality of banana even at conditions favourable for the pathogens.
Abstract: The efficacy of Trichoderma harzianum strain DGA01, sodium carbonate (SC), sodium bicarbonate (SBC) and sodium hypochlorite (SH) applied alone or in various combinations was evaluated in vitro against the most important postharvest pathogens of banana such as Lasiodiplodia theobromae, Thielaviopsis paradoxa, Colletotrichum musae, and Fusarium verticillioides. Trichoderma harzianum DGA01 was compatible with salts at a concentration of 1 % (w/v) as manifested by normal mycelial growth. The efficacy of the fungal antagonist in vitro was enhanced by 10.16–13.06 % in controlling mycelial growth of crown rot pathogens with the addition of salts. After a postharvest dip of fruit for 30 min in 106 conidia of DGA01/mL of 1 % SBC, the incidence of crown rot was reduced by 92 %, but DGA01 combined with SC or SH had no additive effect in controlling crown rot. Thus, DGA01 and SBC was the best combination for crown rot control, with an efficacy similar to synthetic fungicides, and maintained the overall quality of banana even at conditions favourable for the pathogens (22–25 °C, 90–95 % relative humidity).
TL;DR: The newly developed TM-qPCR assay was the most reliable tool for rapidly detecting and quantifying P. sclerotioides in plant and soil samples because its multiplex real-time PCR function allows the adjustment of cycle threshold values with an internal control.
Abstract: We developed a real-time PCR assay using a TaqMan probe (TM-qPCR) for specific detection and quantification of Phomopsis sclerotioides, causal agent of black root rot of cucurbit crops. The design of the primer sets and hybridization probe was based on the internal transcribed spacer region of the ribosomal DNA. The TM-qPCR assay was compared with a conventional, standard PCR (sPCR) assay and on a quantitative real-time PCR (SG-qPCR) assay based on SYBR Green I. The TM-qPCR assay had a detection limit of ca. 0.4 fg of P. sclerotioides DNA, which was approximately 100 times more sensitive than the sPCR assay and almost equivalent to the SG-qPCR assay. The TM-qPCR and SG-qPCR assays both were able to detect various quantities of P. sclerotioides DNA from diseased plants and infested soils, including DNA levels that were not detectable by the sPCR assay. However, the TM-qPCR was advantageous for samples containing PCR-inhibiting substances because its multiplex real-time PCR function allows the adjustment of cycle threshold values with an internal control. Based on the high specificity and sensitivity required for analyzing DNA in natural samples, the newly developed TM-qPCR assay was the most reliable tool for rapidly detecting and quantifying P. sclerotioides in plant and soil samples.
TL;DR: Phage suppression of bacterial palea browning of rice is thought to be due to the combined effects of the phage, naturally inhabiting nonpathogenic bacteria, and the limited susceptible period.
Abstract: Bacterial palea browning of rice, caused by Pantoea ananatis from infection during flowering, occurs widely in Japan and degrades the quality of rice. In a search for environmentally friendly control measures, effects of bacteriophages on the incidence of the disease were examined. Phages lytic to both pathogenic and nonpathogenic P. ananatis were isolated from an inflorescence of eulalia (Miscanthus sinensis), a gramineous weed, and one of the phages was sprayed with and without a nonpathogenic isolate of P. ananatis on rice plants at the flowering stage. Coapplication of the phage and nonpathogenic P. ananatis suppressed the disease in sunlight. Surprisingly, application of the light-labile phage by itself was suppressive. The phage retarded the growth of the pathogen on rice plants and on LB medium. Because nonpathogenic Pantoea strains are abundant on rice panicles at the flowering stage and could be hosts of the phage and the optimum infection period of rice with P. ananatis is during the flowering stage, disease suppression by the phage is thought to be due to the combined effects of the phage, naturally inhabiting nonpathogenic bacteria, and the limited susceptible period.
TL;DR: The ecology and epidemiology of two anthracnose pathogens; practical application of biological control of disease using antagonistic fungi; and development of a simple diagnostic method using an ethanol immersion treatment (SDEI) are studied.
Abstract: This article is an abstract of the paper presented by a winner of the Society Fellowship at the 2013 Annual Meeting of the Phytopathological Society of Japan in Gifu.