Pre‐infection efficacy of resistance inducers against grapevine powdery mildew

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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

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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.

Development and application of a codominant marker of the melon rind colour gene CmAPRR2

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Abstract

Rind colour is an important quality attribute of melon appearance. Identifying target genes and developing functional molecular markers is significant for rind colour breeding in melon. This study involved a genetic analysis of the fruit rind colours of two inbred lines: H185 (with black green melon rind) and H160 (with white rind) alongside a fruit rind colour gene, CmAPRR2. The purpose was to discover the variation sites of the CmAPRR2 gene and develop specific molecular marker for rind colour in melon. The results showed that the black green rind is dominant over white, and single gene controls the colours. A mutation of the G856T base occurred in the eighth exon of the CmAPRR2 coding DNA region in H160, suggesting that this mutation is the key factor for the white rind colour. Thus, a codominant molecular marker, FC, for gene CmAPRR2 was developed and used for molecular identification of 189 F2 individuals. The marker revealed a complete correspondence between genotype and phenotype. Additionally, the marker revealed that the other four white rinds had G856T mutations. This study provides a basis for targeted improvement of melon rind colours, offering a technical means for molecular marker-assisted breeding of melon rind colours.

Validation of sorghum quality control (QC) markers across African breeding lines

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Abstract

Sorghum [Sorghum bicolor (L.) Moench] is a cereal crop of critical importance in the semi-arid tropics, particularly in Africa where it is second only to maize (Zea mays L.) by area of cultivation. The International Crops Research Institute for the Semi-Arid Tropics sorghum breeding program for Eastern and Southern Africa is the largest in the region and develops improved varieties for target agro-ecologies. Varietal purity and correct confirmation of new crosses are essential for the integrity and efficiency of a breeding program. We used 49 quality control (QC) kompetitive allele-specific PCR single nucleotide polymorphism (SNP) markers to genotype 716 breeding lines. Note that 46 SNPs were polymorphic with the top 10 most informative revealing polymorphism information content (PIC), minor allele frequency (MAF), and observed heterozygosity (H o) of 0.37, 0.43, and 0.02, respectively, and explaining 45% of genetic variance within the first two principal components (PC). Thirty-nine markers were highly informative across 16 Burkina Faso breeding lines, out of which the top 10 revealed average PIC, MAF, and H o of 0.36, 0.39, and 0.05, respectively. Discriminant analysis of principal components done using top 30 markers separated the breeding lines into five major clusters, three of which were distinct. Six of the top 10 most informative markers successfully confirmed hybridization of crosses between genotypes IESV240, KARIMTAMA1, F6YQ212, and FRAMIDA. A set of 10, 20, and 30 most informative markers are recommended for routine QC applications. Future effort should focus on the deployment of these markers in breeding programs for enhanced genetic gain.

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

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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

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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

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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

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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.