AbstractSheath blight is one of the most important rice diseases and its control is generally achieved by the use of fungicides, but the economic and environmental costs involved have led to a search for alternative management approaches. In this study, we evaluated the efficacy of eight defence inducers against the rice sheath blight pathogen, Rhizoctonia solani AG1‐IA. The results showed that 10 mM p‐aminobenzoic acid (PABA) and 3 mM vitamin B9 (VB9)‐treated plants had significantly lower disease indices, at 2.56 and 3.49, respectively, compared to the control at 5.36 in growth room conditions. The direct effect studies showed that PABA significantly suppressed fungal mycelial growth, sclerotial formation and hyphal regeneration ability. However, VB9 showed no effect on mycelial growth but promoted sclerotial formation and hyphal regeneration. Histological observation showed a decreased lesion size and lower amount of hyphal DNA in inducer‐treated leaves. Reverse transcription‐quantitative PCR revealed that OsPR1b was significantly induced by VB9 and the expression of OsPR5 was potentiated by PABA, which indicates that the salicylic acid pathway is possibly involved in VB9‐induced resistance, and the antifungal protein OsPR5 probably contributes partially to PABA protection against R. solani. Immediate control effects of PABA and VB9 were also found after disease establishment. Under greenhouse conditions, the control effects of PABA and VB9 were 29.8% and 40.5%, respectively. These findings reveal that the application of PABA and VB9 to complement plant resistance to sheath blight appears to be an effective strategy.

AbstractA new emerging disease of quinoa, quinoa basal stem rot (QBSR), has been recorded in Shanxi Province, China. Observed during the inflorescence emergence stage, the pathogen causes wilting, foliar chlorosis, leaf abscission and eventual death of quinoa. In this study, isolates were identified as Fusarium solani using morphology, molecular and phylogenetic analysis (using sequences of calmodulin, rDNA internal transcribed spacer region, RNA polymerase II B‐subunits RPB1 RPB1 and RPB2 RPB2, and translation elongation factor 1‐α), and pathogenicity analysis. Twenty‐seven isolates were classified into two different groups according to their morphological characteristics, and the mycelial growth rate of Group 2 was higher than that of Group 1 on six different media. The optimum growth temperature for both groups was 30°C and the highest mycelial growth rates were 9.2 and 10.0 mm/day, for Groups 1 and 2, respectively. The sporodochial conidia (SC) and aerial conidia (AC) germinated normally at 15–25°C and 10–40°C, respectively, and the width of SC and AC germ tubes were 1.4 and 2.2 μm. The lethal temperature for AC was 51°C for 20 min, and SC stopped germinating at 45°C. Pathogenicity tests of representative isolates showed that mycelia or conidia caused typical symptoms of QBSR on wounded basal stems of Chenopodium quinoa at 6 days postinoculation. The optimum temperature for the onset of QBSR was 30°C for both groups of isolates, and lesion lengths ranged from 5.4 to 5.9 cm. Knowledge of this pathogen will provide useful information for effective disease management to prevent its spread.

AbstractEntyloma includes pathogenic and saprobic species that infect or colonize dicotyledonous host plants. Although most Entyloma species are known only from native areas of occurrence, some species were introduced with their host plants and spread outside their natural areas. The identification of introduced species is important for detection and management of invasive species. In this study, the morphology, phylogeny and species boundaries of Entyloma eschscholziae, recently introduced from North America to Europe, are revisited. Morphology was similar among the type and other specimens of E. eschscholziae analysed on Eschscholzia californica. Both asexual and sexual morphs were observed. The rDNA ITS1‐5.8S‐ITS2 sequences of the E. eschscholziae specimens from Europe and New Zealand and the environmental sequence obtained from grassland soil in California, United States, were identical. Morphological and molecular analyses confirm that the causative agents of white smut on E. californica in native (North America) and introduced (Europe, New Zealand) areas belong to the same species. DNA barcodes obtained in this study (especially ITS sequence from the designated epitype specimen) could be used to facilitate its molecular identification. Specimens on Dendromecon rigida, previously assigned to E. eschscholziae, are morphologically distinct. An attempt to obtain DNA barcode data from degraded holotype material was not successful and no more recent material is available. However, based on the morphological differences and high host specificity found in Entyloma spp., it is appropriate to describe a new species, Entyloma dendromeconis, for this smut pathogen.

AbstractA collection of isolates of the fungi Leptosphaeria maculans and L. biglobosa, which cause blackleg disease on Brassica napus (canola/oilseed rape) and other Brassicaceae species, was assembled to represent the global diversity of these pathogens and a resource for international research. The collection consists of 226 isolates (205 L. maculans and 21 L. biglobosa) from 11 countries. The genomes of all 205 L. maculans isolates were sequenced, and the distribution and identity of avirulence gene alleles were determined based on genotypic information and phenotypic reactions on B. napus lines that hosted specific resistance genes. Whilst the frequencies of some avirulence alleles were consistent across each of the regions, others differed dramatically, potentially reflecting the canola/oilseed rape cultivars grown in those countries. Analyses of the single‐nucleotide polymorphism (SNP) diversity within these L. maculans isolates revealed geographical separation of the populations. This "open access" resource provides a standardized set of isolates that can be used to define the basis for how these fungal pathogens cause disease, and as a tool for discovery of new resistance traits in Brassica species.

AbstractRice blast is one of the most destructive diseases of rice and is caused by the fungus Magnaporthe oryzae. The disease causes enormous yield losses in rice production worldwide. The rice blast fungus delivers effector proteins into rice cells. The effector proteins play an essential role in fungal virulence by manipulating and controlling host cellular pathways and inhibiting host immune responses to enhance pathogenicity. An effector gene, AvrPi9, which corresponds to the resistance gene Pi9, was cloned and characterized. However, a regulatory molecular mechanism for AvrPi9 gene expression has not been determined. In this study, the genetic variation of the AvrPi9 and its promoter function were characterized. The results showed that 98% (116/118) of the samples carried the AvrPi9 gene without any sequence variation, whilst two isolates, 10576 from Kalasin and NYK56003 from Nakhon Nayok, lacked the AvrPi9 gene. A homeobox domain‐containing protein (MoHOX6) was identified as a candidate transcription factor. The AvrPi9 gene expression was delayed in the MoHOX6 knockout mutant. Moreover, the AvrPi9 promoter was able to drive the expression of a luciferase gene in rice protoplasts. This study provides the first insight into the function and regulation of the AvrPi9 promoter of rice blast fungus.

AbstractUntil recently, the identity of the pathogen of chlorotic streak disease (CSD) was one of the most enduring mysteries of sugarcane pathology. The mystery continued when the causal agent was revealed as a member of a large group of free‐living eukaryotic microbes that had not previously been associated with any plant diseases. CSD has impacted worldwide sugarcane production since at least the 1920s when it was first noticed simultaneously in Java, Australia and Hawaii. Readily identified by irregular, yellow to creamy‐white chlorotic streaks on the leaves, the identity of the pathogen remained unknown for 90 years. CSD negatively affects germination speed, ratooning, stalk numbers and stalk weight, and later causes stunting of crop growth, leading to major losses in sugar production. Prior to the discovery of the pathogen, CSD was found to be waterborne and spread by infected vegetative propagation material. As such it is particularly damaging in poorly drained soils and areas subject to high rainfall. In severe cases it can lead to crop death. The implementation of successful CSD management strategies has been limited by the lack of knowledge surrounding the nature of this disease. However, these strategies are likely to be augmented with the recent identification of the causal agent, a novel cercozoan described as Phytocercomonas venanatans. This review provides insight into the history, causal agent and potential future developments of CSD management strategies.

AbstractPlant‐parasitic nematodes (PPNs) are one of the most damaging pests to plants and are able to cause significant damage to all parts of plants, including stems, leaves, flowers, fruits and roots. Studies on the diversity, host range, distribution and identification methods of PPNs are therefore vital in order to create a basis for management. This current study represents the first dedicated investigation of PPNs from medicinal plants in Vietnam, focusing on the diversity of nematodes associated with 23 different plant species. In combination with a literature review of PPNs in Vietnam, this work has resulted in an updated list of 217 PPN species belonging to 40 genera, 15 families and three orders and also provides a pictorial online key for the identification of 52 most common and important PPN genera of the world. This key is based on the most crucial diagnostic features of PPN females, including female body shape, cuticle, labial shape, cephalic framework, stylet, stylet base, pharynx, median bulb, pharyngeal gland, vulva, tail shape and phasmid. Pictorial representations of these genera and their diagnostic characters are included in the browser‐based key to benefit users from all levels in nematology, be they beginners or experts.

AbstractBoron, in the form of potassium tetraborate, has previously been found to be effective at inhibiting mango black spot disease, caused by Alternaria alternata. However, the mechanisms involved in this inhibition are largely unknown. In this study, A. alternata was treated in vitro with potassium tetraborate at a concentration of 5–10 mM for 48 or 72 h. The intracellular and mitochondrial proteins were extracted from mycelium and separated using two‐dimensional electrophoresis (2‐DE). Differentially expressed proteins (DEPs) were identified using bioinformatics tools and differences between protein spots were derived from mass spectrometry (MS). Using matrix‐assisted laser desorption ionization time‐of‐flight tandem mass spectrometry (MALDI‐ToF‐MS/MS), 96 intracellular and 56 mitochondrial DEPs were identified. The intracellular proteins identified were found to be involved in posttranslational modifications, protein turnover and chaperones, while the mitochondrial proteins were involved in electron transport chains. Our results demonstrate that various metabolic pathways are involved in the antifungal activity of boron. The differential expression of 20 genes was also verified at the mRNA level by reverse transcription‐quantitative PCR. Our study suggests that borate could be used as a potential substitute for synthetic fungicides to control this postharvest disease of mango fruits.

AbstractThe spatiotemporal progress of wheat blast (WB) epidemics within the plant canopy remains poorly known due to complex pathogen–host–environment interactions. Although deterministic methods are popular and useful, robust stochastic methods, such as generalized additive models for location, scale and shape (GAMLSS) and probability matrix or Markov transition model (MTM), have seldom been used to analyse plant disease epidemics. Hence, both methods were employed to derive valuable insights into WB epidemiology at the vertical canopy level. We conducted experiments in three climatic zones in Bolivia, using three wheat cultivars, with disease data corresponding to different canopy positions (lower, L; middle, M; flag leaf, F; and spike, S). Using WB severity data (AUDPC, progress rate and maximum severity [Kmax]), we implemented the GAMLSS and MTM to test our hypothesis that WB is affected by host resistance, location and canopy level. Results showed that the AUDPC, progress rate and Kmax differed across sites, cultivars and canopy positions. Clearly, L and M canopies showed a lower progress rate than F and S. The disease showed an ascending movement from L and M canopies to F and S across locations and cultivars. However, descending transitions also occurred from M to L early or F to M canopy later in the season. Both ascending and descending movements can arise at a single state or several recurrent states, indicating indirect evidence of autoinfection within the canopy before and after spike emergence. Our findings contribute knowledge to improve monitoring and managing WB.