Category Archives: Wiley: Plant Pathology

Gibbsiella quercinecans, a pathogen with an increasing prevalence: A study on the causative agents of bacterial canker of Persian walnut and oak trees in central provinces of Iran

Posted on 10 August 2023 by nSaman Firouzianbandpey, nPejman Khodaygann

The emerging pathogen Gibbsiella quercinecans was found in walnut and oak trees, posing a threat to Persian walnut cultivation in central provinces of Iran.

Abstract

The cultivation of Persian walnuts in Iran is concentrated in the mountainous regions of Zagros and Alborz, encompassing Kohgiluyeh and Boyer-Ahmad, Isfahan and Fars provinces. Historically, these areas were renowned for their abundant growth of oak trees. However, due to environmental stressors, oak populations in the Zagros region have been declining, leading to an increased risk of diseases caused by new and aggressive pathogens, exacerbated by climate change. Understanding the distribution and association of pathogenic bacteria in the environment, especially for less common or uncommon species, has become crucial. In this study, 80 bacterial strains were isolated from 84 symptomatic walnut and 16 symptomatic oak trees to investigate bacterial canker agents in primary walnut cultivation regions of Iran. Following the hypersensitivity test and pathogenicity assays, 21 strains were classed as ‘Brenneria nigrifluens’ or ‘Brenneria-like’, based on their similarities to the reference strain B. nigrifluens ICMP 20120 using phenotypic techniques and specific primers (F1/C3, B. nigrifluens). Varying biochemical characteristics were exhibited by the ‘Brenneria-like’ group in comparison to the ‘B. nigrifluens’ group. Multilocus sequence analysis was performed using the gyrB, rpoB, infB and atpD genes to determine the taxonomic classification of this group, revealing that it belonged to Gibbsiella quercinecans. The increasing reports of this bacterium from different woodland tree hosts suggest its opportunistic role as an individual causative agent, necessitating monitoring of its host expansion and morbidity.

Soybean red crown rot: Current knowledge and future challenges

Posted on 7 August 2023 by nChang‐Jie Jiang, nXianzhi Xien

Soybean red crown rot caused by the soilborne fungus Calonectria ilicicola is emerging as a significant constraint to soybean production worldwide, requiring prompt action.

Abstract

Soybean red crown rot (RCR) is caused by the soilborne fungal pathogen Calonectria ilicicola. It causes root rot, leaf senescence, early defoliation, plant wilting and even death, often resulting in a severe reduction in seed yield and quality. C. ilicicola is an extremely difficult pathogen to control owing to its wide host range and long survival in soil and plant debris. Currently, no practically effective fungicide for this pathogen is available. Breeding for resistance is considered the most effective and environmentally acceptable means of disease management, but no C. ilicicola-resistant soybean variety has yet been identified. Given this situation, it is necessary to promote our understanding of the mechanism of RCR incidence and the development of a comprehensive and sustainable RCR management strategy urgently.

RALF‐like peptide improves the colonization of endophytic Colletotrichum tofieldiae through interacting with plant receptor‐like kinase

Posted on 7 August 2023 by

Endophytic Colletotrichum tofieldiae harbours RALF homologues to regulate symbiotic signals and promote hyphae colonization through interacting with FERONIA encoded by plant.

Abstract

Endophytes can colonize a host plant without inducing obvious disease symptoms. Elicitors from endophytes may play important roles in balancing endophyte colonization. We identified a novel endophytic elicitor from Colletotrichum tofieldiae, CtRALF, that has structural and functional characteristics similar to those of rapid alkalinization factor (RALF) peptides in Arabidopsis thaliana. We found that CtRALF can directly interact with the host plant receptor-like kinase FERONIA (FER). The colonization of FER mutant plants by hyphae of C. tofieldiae was obviously reduced compared with that on wild-type plants. Furthermore, the interaction of CtRALF with FER regulated symbiotic signals by triggering calcium waves, inhibiting reactive oxygen species bursts, increasing mitogen-activated protein kinase phosphorylation and reducing the stabilization of MYC2. Collectively, these results suggested that the RALF homologue of endophytes may improve their symbiosis by interacting with host plant-encoded FER.

Evaluation of different antimicrobial agents for laboratory and field against Pantoea agglomerans, the causative agent of bacterial leaf blight disease on oat (Avena sativa)

Posted on 4 August 2023 by

Laboratory and field experiments on the efficacy of 13 antimicrobial agents against oat leaf blight disease (Pantoea agglomerans) found that zhongshengmycin and ethylicin have excellent control efficacy.

Abstract

Leaf blight disease (LBD) caused by Pantoea agglomerans is a newly emerged oat disease in China that causes great economic and yield losses of oat production. Laboratory and field experiments were conducted to evaluate the efficacy of 13 antimicrobial agents against P. agglomerans and recommend agents with better control efficacy for use. The antibacterial potential of four concentrations of each agent was evaluated under in vitro conditions. Zhongshengmycin and ethylicin were the most effective in inhibiting the growth of P. agglomerans; their bacteriostatic rates (85.0% and 84.8%, respectively) were higher while EC₅₀ lower (0.31 and 0.90, respectively) than other agents. The greenhouse and field experiment suggested that the greatest fresh weight per plant (57.26 g and 57.93 g), forage yield (22.53 t/ha and 22.21 t/ha) and control efficacy (>75%) were obtained after spraying twice with zhongshengmycin or ethylicin in the LBD occurrence phase, with lower yields and control by kasugamycin + dicopper chloride trihydroxide, kasugamycin + oxine copper, benziothiazolinone, copper hydroxide, phenanthrenecarboxylicacid, copper, picoxystrobin, chloroisobromine cyanuric acid, oxathiapiprolin or azoxystrobin. Foliar application of zhongshengmycin or ethylicin can therefore be used for the effective management of LBD of oat.

Potato cyst nematodes: A persistent and fearsome foe

Posted on 1 August 2023 by nValeria Orlando, nEric Boan

This review provides case studies on Globodera pallida, Globodera rostochiensis and Globodera ellingtonae, for a historical view of how scientists and potato experts have responded to PCN pandemics and the effectiveness of management strategies.

Abstract

Nematodes, commonly called roundworms, represent one of the largest phyla of animals. Plant-parasitic nematodes cause significant economic losses in major crops worldwide, and cyst nematodes (Heterodera spp. and Globodera spp.) are among the most damaging species. This review focuses on three main species, Globodera pallida, Globodera rostochiensis and Globodera ellingtonae, collectively known as potato cyst nematodes (PCNs). G. rostochiensis and G. pallida are the most commonly occurring species in potato-growing areas and are considered to have originated from the Andes region in South America and introduced then to Europe in the 1850s and now occur globally in more than 75 countries. PCNs feed entirely inside the root and produce distinctive cysts containing eggs. PCNs reduce root development, stunt the growth of potato plants and ultimately lead to the production of fewer and smaller tubers. PCNs are feared because of their ability to survive for up to 40 years in the soil in the absence of potatoes, and once established they are incredibly difficult to eradicate. Five case studies in this review provide an historical overview of how scientists and potato experts have responded to PCN pandemics and the effectiveness of management strategies.

Contrasting interactions of the aggressive Verticillium longisporum lineage A1/D1 and the non‐aggressive A1/D2 lineage with roots of oilseed rape

Posted on 29 July 2023 by nMarta Vega‐Marin, nAndreas von Tiedemannn

The non-aggressive lineage A1/D2 of Verticillium longisporum penetrates roots of oilseed rape, however, without inducing typical disease symptoms, indicating tolerance in oilseed rape to A1/D2.

Abstract

Verticillium longisporum is a soilborne fungal vascular pathogen of Brassica crops. Three hybrid lineages originating from three independent hybridization events of four haploid Verticillium parents are known. V. longisporum lineage A1/D2 has only been found in horseradish and previous pathogenicity tests have shown that it is non-aggressive on oilseed rape (Brassica napus). The aim of this study was to investigate the interaction of the non-aggressive lineage A1/D2 with oilseed rape in comparison with the aggressive A1/D1 lineage. Although A1/D2 did not cause severe disease symptoms, the study revealed restricted root infection and systemic colonization by this lineage, as assessed by quantitative PCR of fungal DNA. Assessment of root surface colonization by confocal laser microscopy indicated early sporulation, disorganized loosely attached hyphal growth and hyphal coiling of A1/D2. By contrast, A1/D1 showed organized hyphal growth tight to the root surface, as well as hyphal swellings at points of penetration. Vascular colonization was studied with transmission electron microscopy, which revealed less vessel colonization, higher intensity of vascular responses and lower plant cell wall degradation in A1/D2-treated plants in comparison with A1/D1. Vascular responses consisted of strong coating of vessel walls and fungal hyphae with an electron-dense material, indicating higher intensity of plant defence in comparison with A1/D1. The results, for the first time, demonstrate stem colonization and thus a basic level of pathogenic interaction of non-aggressive strains of A1/D2 with oilseed rape associated with a lack of severe disease symptoms, which indicate tolerance in oilseed rape to lineage A1/D2.

Colletotrichum acericola sp. nov. from seeds of the invasive alien tree species Acer negundo in Poland

Posted on 28 July 2023 by

Colletotrichum acericola sp. nov. was found in Wrocław, Poland on the seeds of an invasive alien boxelder. Based on comparisons with US prairie sequences, it is likely that it originated in North America and was introduced to Europe.

Abstract

The boxelder maple (Acer negundo, Sapindaceae) is one of the most common tree species of the genus Acer natively growing in North America. In the 17th century, A. negundo was introduced to Europe as an ornamental plant, and from this time, it started an uncontrolled expansion into new territories, threatening local ecosystems. Fungal development on invasive alien species' seeds and pedicels was observed in 2017 and 2021 in the municipality of Wrocław (Poland), outside of the native occurrence of the host. Morphological analyses combined with multilocus phylogenetic analyses (internal transcribed spacer [ITS], gapdh, act, tub2, chs-1 and his3 sequences) showed that isolates belonged to a new species of Colletotrichum, from the rare C. agaves species complex. The name Colletotrichum acericola is proposed for this fungus. Based on comparisons with sequences from NCBI GenBank originating from prairie plants in the United States, it is likely that C. acericola is native to North America.

Characterization of Xanthomonas hortorum isolates causing leaf spot on Primula vulgaris

Posted on 28 July 2023 by nOmid Shenavar, nHeshmatolah Rahimian, nAli Barzegarn

A new pathovar, Xanthomonas hortorum pv. primulicola, was identified as the causative agent of leaf spot in Primula vulgaris based on taxonomic analysis, and distinct host ranges in comparison to other X. hortorum pathovars.

Abstract

The bacterial leaf spot of Primula vulgaris was reported from forest locations in Mazandaran province, Iran in 1995. The causative bacterium was initially identified as Xanthomonas campestris based on sequences of ITS and 16S rRNA regions. On the basis of sequences of gyrB and dnaK housekeeping genes, the isolates resembled strains of Xanthomonas hortorum. The present study was performed to clarify the taxonomic status of the incitant bacterium. Samples of P. vulgaris with leaf spot symptoms were collected from the Darabkola forest (Mazandaran province) and the bacterial strains were isolated on plates of glucose nutrient agar. Some isolates only induced hypersensitive reaction on geranium (Pelargonium × hortorum) leaves but a few isolates incited leaf spot symptoms when inoculated on P. vulgaris, P. heterochroma and P. × polyantha plants. The isolates were Gram stain, oxidase and urease negative but positive in tests for catalase and hydrolysis of gelatin, aesculin and Tween 80. Several unique nonpathogenic isolates were recovered with varying carbon source utilization profiles and different molecular features, including distinct ERIC-PCR profiles. Representative gyrB, rpoD, dnaK and fyuA housekeeping genes were amplified by PCR and sequenced for comparison with Xanthomonas species in the GenBank database using maximum-likelihood, maximum-parsimony and Bayesian algorithms to construct phylogenetic trees. The pathogenic and nonpathogenic strains were closely related to X. hortorum pathovars. Therefore, it is likely that these isolates belong to a new pathovar of X. hortorum. Based on previous studies and our findings, we propose naming the strain causing primrose leaf spot as X. hortorum pv. primulicola.

Identification of Piper species that are resistant to Phytophthora capsici, Meloidogyne incognita, and waterlogging in Vietnam

Posted on 26 July 2023 by

Two Piper accessions P. divaricatum and P. hancei in Vietnam demonstrated high levels of resistance to pathogenic Phytophthora capsici, the root-knot nematode Meloidogyne incognita and tolerance towards waterlogged conditions.

Abstract

Black pepper (Piper nigrum) is a spice commonly used in kitchens throughout the world. Black pepper production is devastated by a range of pathogenic agents, including Phytophthora capsici and Meloidogyne incognita. Many efforts have been directed towards finding black pepper cultivars that are resistant to these pathogens. In this work, a 39-accession germplasm panel of species in the Piper family collected throughout Vietnam was described. Preliminary tests using P. capsici inoculation onto leaves were carried out to identify potentially resistant accessions. Next, candidate plants were inoculated with P. capsici mycelial suspension and survival rates were assessed 15, 30 and 45 days postinoculation. In addition, Piper plants were challenged with M. incognita by adding larvae/juveniles to growing pots. Resistance to M. incognita was determined by the number of root galls and the percentage of plants with yellow leaves 1, 2 and 4 months after treatment. Piper accessions were also subjected to a 4-day waterlogged treatment. Two accessions (HUIB_PH30 and HUIB_PD36) demonstrated high levels of resistance to all biological and water stresses. Micromorphological characterizations revealed that the amount of intercellular spaces in the root cortex correlated with the resistance to P. capsici and waterlogging tolerance. Hence, the abundance of intercellular spaces can serve as a guide for further selection of black pepper accessions that are resistant to common diseases and tolerant to waterlogged conditions.

Evaluation of soybean genotypes for cowpea mild mottle virus resistance through phenotypic reaction and genotypic analysis

Posted on 25 July 2023 by

Soybean genotypes were screened under field and controlled conditions to identify and characterize, through gene-specific and SSR molecular markers, genotypes resistant against CPMMV infection.

Abstract

Cowpea mild mottle virus (CPMMV), a carlavirus nonpersistently transmitted by whiteflies, is an emerging and economically important virus of soybean. The present study aimed to identify soybean genotypes resistant to CPMMV through mechanical inoculation-based phenotyping and marker trait association using gene-specific and simple-sequence repeat (SSR) markers. A set of 500 soybean genotypes was initially screened in the field for CPMMV infection, of which 288 genotypes showing resistance were evaluated further under controlled glasshouse conditions. Among these 288 genotypes, 43 (14.9%) were resistant, 59 (20.5%) were moderately resistant while the remaining 186 (64.6%) were susceptible. A set of five gene-specific primer pairs, three of which targeted CPMMV R genes, was used for screening the 288 soybean genotypes; 96 genotypes from the 288 (based on disease score) were also genotyped with 24 SSR polymorphic markers for an association study. The mean values of major allele frequency and gene diversity were found to be 0.70 and 0.39, respectively. The polymorphism information content varied from 0.14 to 0.37. Population structure and cluster analysis revealed three subpopulations for the five gene-specific markers and two distinct subpopulations for the 24 SSR markers, respectively. Neighbour joining-based clustering analysis categorized the 288 genotypes into two major clusters. Three markers were found to be significantly associated with CPMMV resistance. The BARCSOYSSR0558 marker showed the highest phenotypic variance of 9.6%. The present study will help in identification of CPMMV R genes and breeding new resistant varieties through marker-assisted selection.