Category Archives: Wiley: Plant Pathology

Transmission of Furcraea necrotic streak virus (FNSV) by Olpidium virulentus

Posted on 11 September 2023 by

Fique plants are source of natural fibre. Furcraea necrotic streak virus (FNSV) causes the most detrimental disease in fique plants, affecting fibre production, and is transmitted by Olpidium virulentus.

Abstract

Furcraea necrotic streak virus (FNSV) is the causative agent of necrotic streak disease, also known as macana in fique crops (Furcraea spp.) resulting in damage to leaf fibres and economic losses. The rhizospheric fungus Olpidium spp. is present in the roots of affected plants and may play a role in the disease transmission. FNSV infection and the role of fungi were examined in macanavirus-diseased plants in Colombia. Spherical, and icosahedral (24.7 ± 1.98 nm), non-enveloped virions with a granular surface were isolated from field fique plants showing signs of macana disease, and the viral genome was completely sequenced. Taxonomic status was assigned through sequence analysis (Macanavirus genus in Tombusviridae family). The variability of the virus pangenome was evaluated in diseased fique plants from ecologically different Andean regions that showed low gene flow. Olpidium virulentus zoospores, identified by internal transcribed spacer (ITS) sequencing and microscopic analysis, were associated with viral particles and resting spores in diseased fique roots. An in vitro virion–zoospore binding assay showed that FNSV and O. virulentus zoospores interacted. Transmission assays in lettuce (Lactuca sativa), a model plant used to study this virus, showed 100% infection when a preincubated mixture of zoospores and FNSV was added to roots, whereas only 33% infection occurred when FNSV was added alone. This demonstrated the ability of O. virulentus to act as a vector for FNSV, potentially enhancing viral transmissibility in field fique crops. This is the first report of FNSV being transmitted by O. virulentus, a rhizosphere fungus.

Genetic diversity of an effector gene, AvrPi9, of rice blast pathogen in Thailand and characterization of its promoter

Posted on 4 September 2023 by

MoHox6, a transcription factor, binds to the AvrPi9 promoter and helps the expression of the AvrPi9 gene in the rice blast fungus during infection and in rice protoplasts.

Abstract

Rice 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.

A streak through history: Solving the riddle of chlorotic streak disease of sugarcane

Posted on 4 September 2023 by nRuby G. Earsman, nAnthony J. Youngn

This review spans the 90 years that passed between the emergence of chlorotic streak disease of sugarcane and the discovery of its pathogen in 2018, and provides epidemiological information on the disease and its management.

Abstract

Until 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.

Diversity of plant‐parasitic nematodes (PPNs) associated with medicinal plants in Vietnam, Vietnamese PPN checklist and a pictorial key for their identification

Posted on 30 August 2023 by

This study reveals the diverse and damaging nature of plant-parasitic nematodes in Vietnamese medicinal plants, providing a Vietnamese nematofauna list of 217 species and offering an online key for global identification.

Abstract

Plant-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.

Intracellular and mitochondrial proteomic analysis reveals antifungal mechanisms of borate on mango black spot pathogen Alternaria alternata

Posted on 29 August 2023 by

The antifungal effect of potassium tetraborate on the proteomics of Alternaria alternata involves multiple metabolic pathways and could be used as a potential substitute for fungicides to control postharvest diseases of mango.

Abstract

Boron, 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.

Multiscale temporal and spatiotemporal analysis of wheat blast infection‐like dynamics using vertical plant stratification, regression and Markov chain approaches

Posted on 21 August 2023 by

Deterministic and stochastic methods identified how WB intensity varies across scales. Temporally, W_SB presented a higher disease intensity than W_LB. At the spatiotemporal level, four types of infection-like changes were estimated.

Abstract

The 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 [K _max]), 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 K _max 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.

The antifungal activity of trans‐cinnamic acid and its priming effect in apple in response to Valsa mali

Posted on 21 August 2023 by

Trans-cinnamic acid not only plays a significant role in inhibiting the growth of Valsa mali, a fungus causing apple Valsa canker disease, but also in priming host defence.

Abstract

Valsa mali causes Valsa canker, one of the most destructive diseases on apple trees, leading to severe losses for the apple industry in China. Considering the development of fungicide resistance and the harmful effects of chemical residues, it is urgent to identify alternatives to control this disease. Trans-cinnamic acid (t-CA), a compound with good antibacterial, antitumour and anti-inflammatory properties, is widely used in food, medicine and other industries. However, the antifungal activity of t-CA against V. mali and its regulatory role in apple defence against biotic stresses are unclear. Based on a metabolomic assay, we found that Malus yunnaensis (Valsa canker-resistant) twigs infected with V. mali dramatically accumulated t-CA. Exogenous application of t-CA effectively inhibited V. mali growth on potato dextrose agar. The EC₅₀ value of t-CA inhibiting mycelial growth was 200 μg/mL. Malus prunifolia (Valsa canker-susceptible) leaves and twigs pretreated with t-CA had significantly enhanced V. mali resistance. The t-CA application increased salicylic acid but reduced jasmonic acid levels in leaves and twigs. Moreover, the contents of phenolic acids and flavonoids increased in t-CA-treated samples. In addition, t-CA increased the activities of phenylalanine ammonia-lyase, β-1,3-glucanase and chitinase. These results indicate that t-CA plays a significant role in inhibiting V. mali growth and priming apple defence.

In silico prediction and analysis of transmembrane‐coiled‐coil resistance gene analogues in 27 Brassicaceae species

Posted on 18 August 2023 by

A total of 6788 transmembrane-coiled-coil (TM-CCs) genes identified across 28 Brassicaceae species may play roles in plant defence and help improve crop disease resistance.

Abstract

The Brassicaceae family is composed of a broad range of species, including the economically important crops from Brassica, Raphanus, Camelina and Sinapis genera. The production of Brassicaceae species, particularly the crop members, is threatened by major diseases. However, the impact of diseases can be minimized or even negated by improving disease resistance. Transmembrane-coiled-coil (TM-CC) genes are a type of resistance gene analogue (RGA) that have been proven to play specific roles in resistance to several diseases. Here, TM-CCs have been predicted in 27 genomes from Brassicaceae genera including Arabidopsis, Arabis, Barbarea, Boechera, Brassica, Camelina, Capsella, Cardamine, Eutrema, Leavenworthia, Lepidium, Raphanus, Sinapis, Sisymbrium, Schrenkiella and Thlaspi. The number of TM-CCs varies throughout the studied genomes, as well as between genera, diploids and polyploids, and Brassica genomes and subgenomes. In total, 6788 TM-CCs were identified, with 708 of them predicted with signalling function, 172 colocalized with previously known disease resistance regions and 70 phylogenetically related to cloned resistance genes, indicating the possible functional involvement of TM-CCs in resistance. This study provides a resource for the identification of functional Brassicaceae TM-CCs along with their clustering and duplication patterns and provides a benchmark for further studies investigating TM-CCs.

Morphomolecular identification and pathogenicity of Colletotrichum species associated with avocado anthracnose in northern Thailand

Posted on 14 August 2023 by nAlireza Armand, nRuvishika S. Jayawardenan

11 Colletotrichum Isolates were identified based on a polyphasic approach from avocado orchards in northern Thailand, and the pathogenicity was assessed for each species on avocado fruits and leaves.

Abstract

Avocado production is restricted globally by the anthracnose disease caused by Colletotrichum species. In Thailand, anthracnose symptoms can be found on avocado leaves and fruits, and it is an important postharvest disease, reducing the shelf life of the fruits and causing huge economic losses. Avocado leaves and fruits showing anthracnose disease were collected from Chiang Rai province, located in northern Thailand, and the Colletotrichum species isolated from the samples were identified based on morphological examination and multigene phylogenetic analyses. Phylogenetic analyses using five loci (ITS, ACT, CHS-1, GAPDH and TUB2) coupled with the morphology of 11 isolates showed that they belonged to four known species of Colletotrichum. Colletotrichum endophytica, C. fructicola and C. siamense are illustrated as new geographical records, and C. henanense is characterized as a new host record. Furthermore, the pathogenicity of these species in avocado fruits and leaves (West Indian variety) has been proven. In addition, this study provides further evidence for the synonymization of C. pandanicola and C. parvisporum with C. siamense.

Overexpression of BnNAC19 in Brassica napus enhances resistance to Leptosphaeria maculans, the blackleg pathogen of canola

Posted on 14 August 2023 by nZhongwei Zou, nW. G. Dilantha Fernandon

Overexpression of BnNAC19 in canola (Brassica napus) can enhance disease resistance against blackleg, caused by Leptosphaeria maculans, providing a valuable genetic resource for disease breeding.

Abstract

Leptosphaeria maculans is a fungal pathogen that causes blackleg disease in canola (Brassica napus), resulting in significant yield and economic losses in Canada and many parts of the world. Plant NAC transcription factors play critical roles in plant development and response to biotic or abiotic stress. In this study, we identified and characterized a BnNAC19 gene from Brassica napus. The overexpression of BnNAC19 in transgenic canola plants contributed to the improvement of seedling resistance against L. maculans. The mycelial growth of a green fluorescent protein-tagged strain of L. maculans and production of pycnidiospores were shown to be inhibited in the transgenic canola plants overexpressing BnNAC19. In addition, the canola transgenic line overexpressing BnNAC19 showed increased disease resistance in the adult plant, which was determined by quantitative resistance. Both increased seedling and adult plant resistance in transgenic canola plants overexpressing BnNAC19 indicate that the BnNAC19 gene plays a positive role against L. maculans. The expression pattern of genes BnNAC19 upstream and downstream of BnNAC19 that participate in plant defence pathways were investigated to elucidate the B. napus resistance mechanisms to L. maculans infection, and hence to aid the long-term blackleg disease-resistant breeding programmes.