Category Archives: Wiley: Plant Pathology

Selective autophagy receptor‐encoding sequences in shallot transcriptome: In silico identification and expression patterns in response to asymptomatic shallot virus X infection

Posted on by
Selective autophagy receptor-encoding sequences in shallot transcriptome: In silico identification and expression patterns in response to asymptomatic shallot virus X infection

Shallot homologues of Nicotiana benthamiana and Oryza sativa P3IP selective autophagy receptors (SARs) have the ability to bind the shallot virus X p11 movement protein and initiate its autophagic degradation, thus carrying dual function as SAR and negative regulators of programmed cell death.


Abstract

Plant host tolerance is a key plant defence response to parasites, including viruses. This complex genetic trait involves multiple molecular mechanisms and, in particular, selective autophagy. Experimental data on the role of various selective autophagy factors and, in particular, cargo receptors in plant tolerance to viral infection are extremely limited. In this communication, I present the results of in silico identification of sequences in the shallot transcriptome encoding homologues of several selective autophagy receptors (SARs) related to the immune response and their expression patterns in response to asymptomatic infection of shallot virus X, a member of the genus Allexivirus, subgenus Acarallexivirus, within the family Alphaflexiviridae. The results obtained, together with the relevant literature data, suggest that some SARs likely to be involved in the regulation of the unfolded protein response and programmed cell death may play an active role in the formation of the state of tolerance of the host plant to allexivirus infection.

Identification and pathogenicity of Colletotrichum species associated with twig dieback of citrus in Western Australia

Posted on by
Identification and pathogenicity of Colletotrichum species associated with twig dieback of citrus in Western Australia

Citrus twig dieback in Western Australia was shown to be caused by Colletotrichum gloeosporioides, C. karstii and C. novae-zelandiae.


Abstract

Up to 32 Colletotrichum species have been reported to be associated with pre- or postharvest diseases of citrus globally, while in Australia, six species have been reported to cause citrus leaf and fruit disease. Twig or shoot dieback has recently been observed as an emerging disease in citrus orchards in Western Australia. Colletotrichum species were isolated from diseased twigs showing dieback (withertip) or lesions, with or without gummosis, collected from 12 varieties of orange, mandarin and lemon. Colletotrichum gloeosporioides sensu stricto, Colletotrichum karstii and Colletotrichum novae-zelandiae were identified using a polyphasic approach that included multigene phylogenetic analysis using sequences of internal transcribed spacer and intervening 5.8S nrDNA (ITS), glyceraldehyde-3-phosphate dehydrogenase (gapdh), β-tubulin (tub2), actin (act) and histone (his3) for isolates in the boninense species complex, and Apn2–Mat1–2 intergenic spacer and partial mating type (Mat1–2) (ApMat) and glutamine synthetase (gs) for isolates in the gloeosporioides species complex, as well as morphological characteristics. C. gloeosporioides was the most prevalent species associated with twig dieback in Western Australia, while C. novae-zelandiae was reported for the first time in Australia. Pathogenicity tests on shoot twigs from lemon and orange trees confirmed C. gloeosporioides, C. karstii and C. novae-zelandiae as the cause of twig dieback, with C. gloeosporioides being the most aggressive species. Knowledge of the species causing twig dieback and their lifestyle will assist the development of integrated control methods.

Comparative genomics identifies genetic markers linked to structural variations that differentiate Puccinia graminis tritici and secalis formae speciales

Posted on by
Comparative genomics identifies genetic markers linked to structural variations that differentiate Puccinia graminis tritici and secalis formae speciales

Newly available genome sequence data were harnessed to design four simple PCR-based assays able to distinguish Puccina graminis formae speciales.


Abstract

Stem rust is a serious disease of many gramineous plants including small grain staples such as wheat, barley, rye and triticale. Separate formae speciales (ff. spp.) of the causal fungus, Puccinia graminis, predominantly infect certain host plant genera. However, despite these taxonomic subdivisions, many P. graminis ff. spp. are genetically too similar to distinguish using existing genetic markers. For those infecting cereals, this is particularly challenging for P. graminis f. sp. tritici (Pgt) and P. graminis f. sp. secalis (Pgs). Herein we harnessed newly available genomic data for 39 Pgt and Pgs isolates and identified four regions of structural variation that were used to design four simple PCR-based assays to distinguish the aforementioned formae speciales. These genomic regions display large presence/absence variation between Pgt and Pgs isolates, and yet a high degree of sequence conservation within shared neighbouring regions, facilitating primer design. We also confirmed lack of amplification in host plant genera analysed, which included assessment of the shared alternate host of Pgt and Pgs, Berberis vulgaris. Accurate classification of P. graminis ff. spp. infections on B. vulgaris is exceptionally valuable to rapidly define plants harbouring P. graminis inoculum when adjacent to cereal crops. Finally, we demonstrated utility of these four genetic markers to correctly distinguish a genetically diverse array of Pgt and Pgs isolates. This strategy could now be readily applied to other pathogens of interest, which will be of increasing value as genomic resources continue to rapidly expand for many key biotic threats to agricultural productivity.

Pre‐infection efficacy of resistance inducers against grapevine powdery mildew

Posted on by
Pre-infection efficacy of resistance inducers against grapevine powdery mildew

PRIs can be used when PM infection risk is considered, and based on preventative treatments applied between 1 to 3 days before Erysiphe necator infection, depending on the product.


Abstract

Plant resistance inducers (PRIs) are of increasing interest for disease control in sustainable viticulture, but their efficacy in vineyards is still under investigation. We studied the effects of four commercial PRIs, of natural and microbial origin, on the development of powdery mildew (PM) on grapevine leaves over a 3-year period. Disease and sporulation severity were evaluated following the artificial inoculation of PRI-treated leaves with Erysiphe necator conidia at 1, 3, 7 and 12 days after treatment (DAT). Laminarin (LAM) and cos-oga (COS) were the most effective in reducing both disease (57.1% and 49.5%, respectively) and sporulation (85.3% and 90.2%, respectively) severity; the reduction in PM severity provided by cerevisane (CER) was lower (27%), and that of Pythium oligandrum (PYT) was intermediate (44.9%). LAM was effective from 1 DAT, while COS and PYT were more effective when E. necator was inoculated at 7 to 12 DAT. These results open new perspectives on how PRIs are used as single, preventative interventions performed 1 to 3 days before E. necator infection, depending on the product used. The effect of PRIs on the sporulation of E. necator colonies also suggests a broader and longer effect on PM epidemics.

The Ralstonia solanacearum effector RipV1 acts as a novel E3 ubiquitin ligase to suppress plant PAMP‐triggered immunity responses and promote susceptibility in potato

Posted on by
The Ralstonia solanacearum effector RipV1 acts as a novel E3 ubiquitin ligase to suppress plant PAMP-triggered immunity responses and promote susceptibility in potato

Ralstonia solanacearum requires the type III effector RipV1 to exhibit its virulence role, which acts as a novel E3 ubiquitin ligase to suppress plant PAMP-triggered immunity responses and promote susceptibility.


Abstract

Bacterial wilt caused by Ralstonia solanacearum is a destructive plant disease, particularly in potato (Solanum tuberosum). R. solanacearum deploys a diverse and potent arsenal of type III effectors to inhibit the plant immune system. However, the understanding of individual effectors promoting susceptibility in host plants and interfering with plant immunity responses is still limited. Here, we demonstrated that the type III effector RipV1 functioned as a novel E3 ubiquitin ligase (NEL) effector and exhibited E3 ubiquitin ligase activity in vitro. Transient expression of RipV1 suppressed plant pathogen-associated molecular pattern (PAMP)-triggered immunity (PTI) responses in Nicotiana benthamiana, such as the expression of PTI-related genes and the reactive oxygen species (ROS) burst. Prolonged expression of RipV1 induced cell death in N. benthamiana leaves. Notably, mutating the conserved cysteine residue of RipV1 abolished its E3 ligase activity and its ability to suppress plant PTI responses. This study also revealed the indispensability of RipV1 for R. solanacearum's full virulence in potato. Transgenic potato plants overexpressing ripV1 but not the catalytic mutant ripV1-C444A displayed enhanced susceptibility to R. solanacearum. RipV1 was observed to localize specifically to the plant plasma membrane, with its N-terminus being pivotal in determining this localization. These findings showcase that RipV1 acts as a NEL effector and contributes to R. solanacearum virulence by suppressing plant PTI responses through its E3 activity.

A new genus and species of Cryphonectriaceae causing stem cankers on plantation eucalypts in South Africa

Posted on by
A new genus and species of Cryphonectriaceae causing stem cankers on plantation eucalypts in South Africa

A causal agent of a stem canker disease on eucalypts discovered in KwaZulu-Natal province is clarified as a new genus in the Cryphonectriaceae, for which the name Xanthoporthe myrticola is provided.


Abstract

Fungi in the Cryphonectriaceae are important canker pathogens of woody shrubs and trees in the Melastomataceae and Myrtaceae (Myrtales). During 2021 disease surveys in KwaZulu-Natal (South Africa) plantations, a serious stem canker disease was discovered on species of Eucalyptus and Corymbia. The cankers had structures on their surfaces typical of fungi in the Cryphonectriaceae. The aims of the study were to identify the fungus associated with the disease and to test its pathogenicity. Morphological characteristics of both sexual and asexual structures and phylogenetic analyses based on partial sequences of the conserved nuclear large subunit (LSU) ribosomal DNA, the internal transcribed spacer (ITS) regions including the 5.8S gene of the ribosomal DNA operon, and two β-tubulin (BT1/BT2) regions were used for identification purposes. Phylogenetic analyses of the sequence data and morphological characteristics supported the establishment of a new genus in the Cryphonectriaceae, for which the name Xanthoporthe myrticola gen. et sp. nov. is provided. Pathogenicity trials showed that isolates were pathogenic on tested Eucalyptus grandis and hybrids as well as Corymbia henryi. The results suggest that this is an emerging pathogen that could influence the sustainability of plantation forestry in South Africa.

Barley powdery mildew control in Western Australia and beyond

Posted on by
Barley powdery mildew control in Western Australia and beyond

This review discusses the challenging nature of barley powdery mildew and management strategies used in Western Australia, and the wider context of how scientists and breeders have responded to epidemics.


Abstract

Australia is one of the largest barley exporters in the world, with Western Australia accounting for some 40% of national production. The crop is predominantly grown in the south and south-west of the state in winter and spring, where temperate conditions and higher rainfall levels are more suited to barley than northern and eastern regions. Between 2007 and 2013, prolonged outbreaks of barley powdery mildew (BPM) occurred. This was brought about by a combination of the extensive use of susceptible cultivars and an over-reliance on a small number of single mode-of-action demethylation inhibitor fungicides, which select for mutations in the C14α-demethylase (Cyp51A) gene. This review highlights the steps taken to reduce losses to BPM, breeding efforts to introduce resistance into cultivars and the success of pre-breeding research to find new and durable resistance genes. We also draw comparisons with powdery mildew in Australian wheat, where similar factors are leading to substantial outbreaks.

Passionfruit severe leaf distortion virus: Expanded host range, response of Passiflora spp. plants to infection and transmission by Bemisia tabaci MEAM1

Posted on by
Passionfruit severe leaf distortion virus: Expanded host range, response of Passiflora spp. plants to infection and transmission by Bemisia tabaci MEAM1

Passion fruit severe leaf distortion virus was not transmitted by Bemisia tabaci to plants of three out of 13 Passiflora species tested. Only P. malacophylla plants grafted onto PSLDV-infected passion fruit plants were not infected.


Abstract

Passionfruit severe leaf distortion virus (PSLDV) is a begomovirus transmitted by Bemisia tabaci Middle East-Asia Minor 1 (MEAM1), associated with severe disease in passion flowers. This study aimed to evaluate the reaction of plants of different species of Passiflora to infection with PSLDV, expand the known host range of the virus and determine the minimum virus acquisition and inoculation access periods and the time of virus retention by B. tabaci MEAM1. Plants of Passiflora cincinnata, P. mucronata and P. malacophylla were not infected with PSLDV through transmission with B. tabaci MEAM1. When healthy plants of these species were fork grafted onto PSLDV-infected plants of P. edulis, only plants of P. malacophylla remained uninfected and the virus was not detected by PCR, suggesting immunity to this begomovirus. Plants of Datura stramonium, Nicotiana benthamiana, N. clevelandii, N. tabacum ‘Xanthi’, Solanum lycopersicum (tomato cv. Compack) and several varieties of Manihot esculenta (cassava cvs IAC 118-96, IAC 6-01, Paranavaí, IAC 576, IAC 90 and IAC 14) were susceptible to infection with PSLDV through transmission with B. tabaci MEAM1. Adults of B. tabaci MEAM1 acquired PSLDV after 1 h of feeding on PSLDV-infected plants of D. stramonium. They transmitted the virus to healthy plants after feeding on these plants for 1 h, although with low transmission rates. The retention time of PSLDV in the vector was 14 days.

Phylogenetic, metabolic and pathogenic characteristics of Alternaria alternata strains from wheat in China

Posted on by
Phylogenetic, metabolic and pathogenic characteristics of Alternaria alternata strains from wheat in China

Alternaria alternata dominated in wheat grains from China with high toxin production capacity and distinct pathogenicity to wheat and apple.


Abstract

Alternaria is an important toxigenic fungal genus endangering the quality of cereal grains. No data are available in the literature regarding the composition of Alternaria species in wheat from the main wheat-cultivating regions of China. In this study, a total of 282 strains were isolated from wheat kernels collected in various provinces. Phylogenetic characterization was performed using two informative loci, ASA10 and ASA19, demonstrating that all strains belonged to A. alternata. A low molecular diversity was observed, which did not appear to be influenced by geographic origin. The secondary metabolite profile of the strains was evaluated in rice culture. Altertoxin I was synthesized at a high concentration by the majority of the strains, while the accumulation of altenuene was lower in both frequency and level than that of alternariol and its derivative. A. alternata did not cause readily observable symptoms on wheat spikes after spraying of the conidia at anthesis, but a higher quantity of altertoxin I and Alternaria DNA were detected in inoculated grains. Artificial inoculations of apple fruit showed that all examined strains were capable of causing typical rot symptoms and producing all four toxins to a certain degree. The widespread occurrence of A. alternata on wheat grains and its ability to synthesize various toxic metabolites may pose a serious hazard for both growers and consumers.

Optimization of concentration parameters for maximizing bacteriophage recovery value using response surface methodology: A case study on determining the optimal concentration parameters for Erwinia amylovora EA1T1.B3 phage

Posted on by
Optimization of concentration parameters for maximizing bacteriophage recovery value using response surface methodology: A case study on determining the optimal concentration parameters for Erwinia amylovora EA1T1.B3 phage

Response surface methodology combined with a three-factor central composite design optimized recovery in phage concentration, achieving a maximum recovery rate of 85.37% with 18% PEG, 2.38 M NaCl, and 0 h incubation time.


Abstract

Bacteriophages have emerged as effective antimicrobial agents in combating pathogenic bacteria. To successfully apply phages in real-life scenarios, it is crucial to optimize their large-scale production, concentration and purification processes. In this study, our objective was to optimize the phage concentration parameters with a high recovery rate within a shorter time and minimum chemical consumption. We isolated and characterized a specific Erwinia amylovora phage. Subsequently, we employed response surface methodology (RSM) combined with a three-factor central composite design to optimize the phage recovery. The factors considered were polyethylene glycol (PEG) concentration, NaCl concentration and incubation time. The optimized values for PEG, NaCl and incubation time, which resulted in a maximum recovery rate of 85.37%, were determined as 18%, 2.38 M and 0 h, respectively. This finding indicates that the concentration step, which traditionally took up to 18 h with a recovery rate of 65%, can now be accomplished in a significantly shorter time with an improved recovery rate. Our study demonstrates the effectiveness of RSM to identify the optimum conditions for phage precipitation. This approach allows for the rapid and efficient design of precipitation protocols tailored to specific bacteriophages, resulting in shorter processing times and higher recovery rates.