Category Archives: Wiley: Plant Pathology

Overexpression of an NLP protein family member increases virulence of Verticillium dahliae

Posted on 30 January 2024 by

The role of VdNEP, an NLP protein gene, in virulence was investigated by overexpressing the gene in multiple pathotypes and monitoring its cellular localization during infection.

Abstract

Verticillium dahliae is a xylem-invading fungal pathogen that causes vascular wilt in a wide range of angiosperms. The pathogen uses a variety of virulence factors to invade and colonize its hosts. Here, we report that VdNEP, an NLP (Necrosis and ethylene inducing peptide 1-Like Protein), functions as one such factor in multiple hosts. Eggplant leaves treated with VdNEP developed necrotic symptoms. Overexpression of VdNEP by incorporating extra copies of the VdNEP gene increased virulence to cotton, eggplant and tomato plants, suggesting its role as a virulence factor in diverse plants. Increased expression of VdNEP among the transformants did not correlate with the number of VdNEP inserts, suggesting that its expression was affected by the genomic context of the insertion sites. Interestingly, a transformant derived from a defoliating strain with high VdNEP transcript levels caused disease symptoms in tomato plants, whereas the corresponding wild-type strain did not cause visible symptoms. The amount of V. dahliae DNA in plants infected with this VdNEP-overexpressing transformant was 22 times higher than that in plants infected with the wild-type isolate, further supporting the critical role of VdNEP in infection. A VdNEP-EGFP fusion was constructed to follow its localization in fungal cells and during infection.

Unravelling the aetiology of Dickeya zeae using polyphasic approaches for bacterial stalk rot in maize

Posted on 30 January 2024 by

This study identifies and molecularly characterizes Dickeya zeae isolates from bacterial stalk rot of maize, using six genomic regions (16S rRNA, recN, gyrB, dnaX, recA and dnaJ) using multiple phylogenetic analyses.

Abstract

Bacterial stalk rot (BSR), caused by Dickeya zeae (syn. Erwinia chrysanthemi pv. zeae), has emerged as a significant disease affecting maize crops worldwide. In this study, symptomatic maize plants were collected from diverse agroclimatic zones in India over the period of kharif 2019–2021. Various approaches, including pathogenicity tests, cultural characteristics, biochemical profiling and molecular analysis, were employed to accurately identify the collected bacterial isolates as Dickeya. Pathogenicity assessments were conducted on 40-day-old maize plants, following Koch's postulates, as well as through potato maceration assays. Furthermore, cross-infectivity studies were conducted on rice, potato, tomato and banana plants. Phenotypic and biochemical characterization confirmed that all the isolates belonged to the Dickeya genus. Additionally, PCR amplification of a pel gene fragment, specific to the genus Dickeya, further verified the pathogenic isolates as Dickeya. Molecular characterization studies were performed on four isolates (UKMDZ-3, PBMDZ-7, TSMDZ-11 and HPMDZ-16), selected to represent distinct maize agroclimatic zones and four states of India, and which caused severe infections on susceptible maize cv. Early Composite. Amplification of six characteristic genome regions (16S rRNA, recN, gyrB, dnaX, recA and dnaJ) from these isolates facilitated individual and concatenated gene phylogenetic analyses, confirming their resemblance to Dickeya zeae. This study represents the first comprehensive molecular analysis of D. zeae isolates from India, providing valuable insights for future crop improvement strategies. The findings contribute to our understanding of the genetic basis of BSR in maize and offer potential avenues for genetic enhancement to mitigate the disease's impact on maize cultivation.

Rice leaf disease detection based on enhanced feature fusion and target adaptation

Posted on 28 January 2024 by

The proposed EFFTAN model was validated for robustness and generalization of four rice leaf spot data plus maize data samples, and the experimental data demonstrated the significance and validity of the research work.

Abstract

Intelligent rice disease recognition methods based on deep neural networks can predict the degree of disease on the basis of, for example, the number of disease spots on an image, so that preventive measures can be taken. Currently, intelligent recognition methods for rice diseases suffer from the disadvantages of poor versatility and low accuracy. This paper uses eight common image classification networks to classify and identify four rice diseases. ResNet50 was selected as the feature extraction network and an enhanced feature fusion and target adaptive network (EFFTAN), referred to as EFFTAN, is proposed. The EFFTAN was used to detect four rice spot diseases in the rice leaf disease image samples dataset; the mean average precision of the final detection was 95.3%, and effective detection was also achieved for the dense spot features.

Influence of berry ripening on susceptibility to Coniella diplodiella infection in grapevine

Posted on 25 January 2024 by nTao Ji, nLanguasco Luca, nIrene Salotti, nMing Li, nVittorio Rossin

The data from in vitro and in vivo trials showed that grape clusters were susceptible to infection by Coniella diplodiella for a long period; effective disease control therefore requires interventions from early berry development.

Abstract

White rot, caused by the fungus Coniella diplodiella, is an important but poorly studied disease that mainly affects grapevine clusters. White rot control typically involves the repeated application of fungicides, which may be unjustified in some cases given that the key period of berry susceptibility to infection remains unclear and controversial. In this study, germination of C. diplodiella conidia and mycelium growth were investigated on water agar (conidial germination only) and artificial media similar to berry juice at five growth stages from pea-sized to berries ripe for harvest. On water agar, conidia germinated from 10°C to 35°C (with an optimum of 20–30°C) with >2 h of moisture incubation. Both conidial germination and mycelial growth were higher on agar similar to berry juice at véraison to berry softening than at other stages, with the lowest values detected for the ripe berries. The berries were also artificially inoculated with conidia at the different growth stages, showing that grape clusters were susceptible to infection for a long period, albeit with varying degrees of susceptibility at different stages. This implies that effective disease control requires interventions from early berry development, whenever weather conditions are conducive to infection. Further development of a predictive model accounting for weather conditions and berry susceptibility dynamics would facilitate the dynamic estimation of the disease risk during the grapevine-growing season and contribute to a risk-based application of fungicides for white rot control.

Differential expression of antimicrobial metabolites, phenylpropanoid and phytohormone metabolic pathway genes determines resistance or susceptibility to Ascochyta rabiei in chickpea

Posted on 25 January 2024 by

Defence to Ascochyta rabiei in chickpea is composed of a two-tier system separated by time wherein jasmonic acid, phenylpropanoids, antimicrobial peptides and defence genes govern resistance and abscisic acid susceptibility.

Abstract

Blight caused by Ascochyta rabiei is a major constraint in the productivity of chickpea (Cicer arietinum). The mechanisms governing resistance/susceptibility to blight in chickpea are poorly understood. We used a blight-resistant (HC1) and a blight-susceptible (GPF2) genotype of chickpea and genes of pathogenesis-related proteins (PRPs), phenylpropanoid pathway metabolites, abscisic acid (ABA), gibberellic acid (GA) and jasmonic acid (JA) to understand the role of these in A. rabiei resistance/susceptibility. The JA, ABA and GA biosynthesis genes of chickpea were retrieved, characterized and gene-specific primers were used for transcriptional studies. Gene expression revealed that chickpea activated its defences rather quickly and well before initiation of spore germination. In resistant HC1, the majority of the JA, GA and phenylpropanoid pathway genes had peak maxima at 2 h post-inoculation (hpi) whereas PRPs/defence genes had peak maxima at 24/36 hpi implying that defence to A. rabiei in chickpea is composed of a two-tier system separated by time: immediately after spore attachment and at or just prior to host penetration. Unlike HC1, susceptible GPF2 was late in activation of defence responses or did not activate them. Another striking difference between HC1 and GPF2 was up-regulation of ABA biosynthesis genes in inoculated GPF2 and down-regulation in HC1. This study revealed that phenylpropanoids, PRPs, JA, 8-(1R,2R)-3-oxo-2-(Z)-pent-2-enyl cyclopentyl octanoate, (15Z)-12-oxophyto-10,15-dienoic acid and methyl-jasmonate govern resistance to A. rabiei in chickpea whereas ABA governs susceptibility.

Transcriptional profiling identifies the early responses to Puccinia triticina infection in the adult plant leaf rust resistant wheat variety Toropi

Posted on 25 January 2024 by

The wheat cv. Toropi displays a durable leaf rust resistance that is associated with a prehaustorial resistance phenotype and rapid changes in wheat gene expression following Puccinia triticina inoculation.

Abstract

Leaf rust, caused by Puccinia triticina (Pt), is a major disease of wheat and a significant problem for wheat production in Brazil. The Brazilian variety Toropi, released in 1965, has maintained high levels of field, adult plant resistance (APR) to leaf rust across global locations, while microscopic studies have indicated prehaustorial resistance mechanisms. Analyses of gene expression in flag leaves of Toropi, during the early stages of Pt infection, were undertaken to explore the mechanisms behind the APR in Toropi. Differential expression of wheat genes was undertaken, comparing Pt- to mock-inoculated and Pt- to Pt-inoculated time points. Analysis of gene expression indicated a strong response to Pt, which was fully active by 6 h after inoculation (hai). More genes were downregulated than upregulated, particularly at 6 and 12 hai. Gene Ontology enrichment analysis indicated a shutting down of RNA and protein synthesis and an early effect on photosynthesis, with disruption of the electron transfer chain. Analyses of upregulated genes identified genes involved in ATP-binding and protein kinase activity at 6 hai, supporting a rapid metabolic response to Pt infection. A general upregulation of genes involved in transport and metabolism indicated the need to relocate protein and organic-based resources. Alignment of differentially expressed genes with the genomic regions defining four leaf rust APR quantitative trait loci (QTLs) in Toropi identified candidate resistance genes, including a sugar transporter, a receptor kinase and a seven-transmembrane MLO family protein. In addition, 60 Pt genes were identified, 11 being annotated as potential effector proteins.

Diagnostics of Fusarium wilt in banana: Current status and challenges

Posted on 22 January 2024 by

This review highlights challenges in the detection of Fusarium wilt TR4 in banana through a critical assessment of published diagnostic methods and their validation in light of existing genetic diversity in pathogen populations.

Abstract

Global banana production is under threat from the rapidly spreading pathogen Fusarium oxysporum f. sp. cubense (Foc) tropical race 4 (TR4), which is pathogenic to Cavendish and many other varieties. Due to the absence of effective control methods and the lack of other market-acceptable resistant cultivars, early diagnostics, containment and quarantine measures are important to limit further spread and impact of this pathogen. Early detection and identification of the pathogen require reliable diagnostic assays. The reliability of a molecular diagnostic assay is directly linked to the rigour applied at validating the assay according to predetermined standards. For specific detection of a target pathogen using molecular diagnostics, a well-resolved taxonomy of the target and related species based on their evolutionary relationships is also required. The advent of sequence-based phylogenetic analysis has given rise to new insights regarding the taxonomic classification of Foc and provided proof for the polyphyletic origin of Foc races, complicating early and reliable detection of the pathogen. Although numerous diagnostic methods for Foc have been developed, choosing a rigorously validated and fit-for-purpose method for adoption is currently challenging as advantages and drawbacks for each assay are not always obvious or put into context with prior methodologies. This review compiles and critically dissects published methods that are reported to detect Foc to date and highlights their benefits and constraints to provide a valuable reference for diagnosticians, researchers and policy makers worldwide.

Volatile organic compounds as potential biomarkers of Cadophora luteo‐olivacea presence on kiwifruits

Posted on 22 January 2024 by

The results suggested that the volatile compounds are released during the early phase of the interaction between kiwifruit (host) and Cadophora luteo-olivacea (pathogen).

Abstract

Cadophora luteo-olivacea is the causal agent of the skin-pitting disease of kiwifruit, a syndrome that appears after 4–5 months of cold storage. However, it is assumed that the infection takes place in the field during fruit development. The present work takes into consideration the production of volatile organic compounds (VOCs) of Actinidia deliciosa ‘Hayward’ at different phenological phases as potential C. luteo-olivacea infection biomarkers. In vitro assays were conducted to gain knowledge on the effect of kiwifruit VOCs on pathogen conidial germination and mycelial growth. VOCs produced by kiwifruit either inoculated or not with C. luteo-olivacea were analysed at different phenological phases by SPME/GC–MS analysis. In particular, ethanol, o -xylene, d-limonene and acetic acid showed a significant increase in the presence of fungal inoculation. Ethanol and d-limonene were also detected as volatile metabolites of the pathogen. The effect of each compound (ethanol, o -xylene, d-limonene and acetic acid) was tested on the fungal conidial germination at different concentrations, showing a growth stimulation at lower amounts. These results show how the production of some VOCs can contribute to the knowledge of fruit–pathogen interaction in the field with the aim of developing future tools for early disease detection and consequent effective control.

Modelling the displacement and coexistence of clonal lineages of Phytophthora infestans through revisiting past outbreaks

Posted on 18 January 2024 by nChih‐Chiang Huang, nEdward C. Y. Liew, nJustin S. H. Wann

A simulation model with pathogenesis parameters as inputs was developed to predict the changes in lineage proportions of Phytophthora infestans on potato and tomato crops.

Abstract

The continuous changes in the lineage proportions of populations in the clonal plant pathogen Phytophthora infestans on potato and tomato crops have been perplexing to researchers and disease managers. Sudden outbreaks of newly emergent genotypes are often associated with these rapid composition changes. Modelling can predict the persistence and displacement of pathogen genotypes with differential fitness among hosts. Building upon previous models, we combined analytical and simulation methods to model the outcome of interactions between competing lineages on different hosts. Model inputs include pathogenesis parameters, and the outputs are fitness and lineage proportions within each host. Analytical solutions yielding complete displacement, partial coexistence-displacement and complete coexistence were described. In a retrospective study, the lesion growth rate and sporulation density of P. infestans lineages on potato and tomato from pathogenicity trials were used as inputs. Output lineage frequencies were compared with historical epidemiological situations to check model accuracy. The results showed that pathogenesis traits measured from empirical trials could simulate lineage constituents on potato and tomato and estimate genotypic fitness with reasonable accuracy. The model also showed promise in predicting ongoing lineage displacements in the subsequent year or few years, even when the displaced lineage was still highly prevalent during the time of isolation. However, large uncertainties remain at temporal–spatial scales owing to complex meta-population dynamics in some regions and adaptation to local environmental factors. This simulation model provides a new tool for forecasting pathogen compositions and can be used to identify potentially problematic genotypes based on pathogen life-history traits.

Unveiling mechanisms for induced systemic resistance, resistance breeding and molecular marker‐assisted breeding against Phomopsis blight of Solanum melongena

Posted on 18 January 2024 by

This paper reviews resistance in eggplant (brinjal) cultivars against Phomopsis vexans via heterosis breeding, induced resistance, grafting and marker-assisted techniques.

Abstract

Phomopsis vexans is one of the most destructive fungal pathogens associated with eggplant and currently poses a significant threat to eggplant production worldwide. The detrimental impact of P. vexans on eggplant yield has been extensively explored by various mycologists who have conducted thorough studies on the diversity, pathology and biological aspects of the pathogen. However, achieving enduring resistance or effective management has proven to be a challenge thus far. PCR-based detection and molecular association of Phomopsis resistance use molecular markers to examine the potential for heterosis in various crosses, aiming for premium hybrids with genetic resistance and high-yielding capabilities. The latest genome sequencing methods and availability of a wider range of genetic diversity has enabled the breeding of resistant varieties of eggplant. This review provides a detailed description on P. vexans including its epidemiology, dispersal methods, symptomology, colony characteristics, taxonomy and evolution of its strains. Different resistance breeding techniques including heterosis breeding, host plant resistance, identification of resistant sources, inheritance pattern for Phomopsis resistance, importance of grafting to impart resistance, significance of induced resistance, PCR-based detection and molecular association of Phomopsis resistance are explained. Future approaches include molecular marker techniques such as genome-wide association studies, sequence-characterized amplified regions (SCAR), role of biotic inducers, pathogenesis-related proteins and plant growth-promoting rhizobacteria against Phomopsis blight of eggplant.