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Disease phenotypes following inoculation with Colletotrichum trifolii and Erysiphe pisi. A, Disease score index (DSI) established using detached leaflets of Medicago truncatula inoculated with C. trifolii at 8 days post inoculation (dpi). One drop of conidia was applied to each leaflet and symptoms were scored into six classes, where 1 = no symptom or only a few isolated necrotic cells; 2 = scattered necrotic cells; 3 = chlorotic area beneath inoculation droplet; most of leaf green; 4 = severely chlorotic leaf and large necrotic lesions; 5 = large necrotic area with dark-brown border, detection of acervuli, severe chlorosis, or both; and 6 = large macerated areas that were observed as soon as 3 dpi beneath inoculum droplet, and severe chlorosis. Arrows indicate the points of inoculation. B, Disease index established on leaves of M. truncatula inoculated with E. pisi at 10 dpi; 1 = complete resistance, no macroscopic symptoms; 2 = partial susceptibility, patches of mycelium were detected but did not coalesce; and 3 = full susceptibility, trifoliate leaves were totally covered by mycelium. C, DSI means were first calculated with six to nine inoculated leaflets for each independent repeat. Final DSI values were obtained by calculating DSI means of three to five repeats for each recombinant inbred line. D, DSI means were calculated from scores recorded during two independent repeats. Arrows on C and D indicate the DSI of parental lines. A = A17; F = F83005.5; D = DZA315.16; 1 or 2 indicates the DSI obtained following inoculation by C. trifolii race 1 or race 2, respectively; and A or P indicates the DSI following inoculation with Ep-a or Ep-p, respectively.
Source publication
Medicago truncatula was used to characterize resistance to anthracnose and powdery mildew caused by Colletotrichum trifolii and Erysiphe pisi, respectively. Two isolates of E. pisi (Ep-p from pea and Ep-a from alfalfa) and two races of C. trifolii (races 1 and 2) were used in this study. The A17 genotype was resistant and displayed a hypersensitive...
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Citations
... M. truncatula (2n = 2x = 16), a member of the Medicago genus, has been used as a model species of legume (Barker et al., 1990;Cook, 1999). A17-Jemalong is one genotype of M. truncatula with high resistance to many diseases such as anthracnose and powdery mildew (Ameline-Torregrosa et al., 2008a). Therefore, it was selected as the target species for syntenic analysis with M. ruthenica. ...
Medicago ruthenica, important forage in the legume family, possesses high nutritional value and carries abundant tolerance genes. This study used whole-genome data of M. ruthenica to perform a genome-wide analysis of the nucleotide-binding site-leucine-rich repeat receptor (NLR) gene family, which is the largest family of plant disease resistance genes (R genes). A total of 338 NLR genes were identified in the M. ruthenica genome, including 160 typical genes that contained 80 coiled-coil (CC)-NBS-LRR (CNL) genes, 76 toll/interleukin-1 receptor (TIR)-NBS-LRR (TNL) genes, four resistance to powdery mildew 8 (RPW8)-NBS-LRR (RNL) subclass genes, and 178 atypical NLR genes encoding proteins without at least one important domain. Among its eight chromosomes, M. ruthenica chromosomes 3 and 8 contained most of the NLR genes. More than 40% of all NLR genes were located on these two chromosomes, mainly in multigene clusters. The NLR proteins of M. ruthenica had six highly conserved motifs: P-loop, GLPL, RNBS-D, kinase-2, RNBS-C, and MHDV. Phylogenetic analysis revealed that the NLR genes of M. ruthenica formed three deeply separated clades according to the N-terminal domain of the proteins encoded by these genes. Gene duplication and syntenic analysis suggested four gene duplication types in the NLR genes of M. ruthenica, namely, tandem, proximal, dispersed, and segmental duplicates, which involved 189, 49, 59, and 41 genes, respectively. A total of 41 segmental duplication genes formed 23 NLR gene pairs located on syntenic chromosomal blocks mainly between chromosomes 6 and 7. In addition, syntenic analysis between M. truncatula and M. ruthenica revealed 193 gene pairs located on syntenic chromosomal blocks of the two species. The expression analysis of M. ruthenica NLR genes showed that 303 (89.6%) of the NLR genes were expressed in different varieties. Overall, this study described the full NLR profile of the M. ruthenica genome to provide an important resource for mining disease-resistant genes and disease-resistant breeding.
... To develop more knowledge on legumes, Medicago truncatula get more attention because of its small genome (500-550 Mpb) (Young et al., 2005) and its short growth cycle. This model plant is the subject of numerous researches that studies the symbiotic and the mycorrhizal symbiosis (Ané et al., 2004), the abiotic stress tolerance (Narasimhamoorthy et al., 2007), the disease resistance (Ameline-Torregrosa et al., 2008). But what are the physiological characteristics of this model plant under controlled conditions? ...
... While the genetic basis of southern anthracnose resistance in red clover is largely unknown, resistance to Colletotrichum spp. has been studied in other legume species including soybean, common bean, and the model species M. truncatula (Ameline-Torregrosa et al. 2008;Yang et al. 2008). ...
Key message
High variability for and candidate loci associated with resistance to southern anthracnose and clover rot in a worldwide collection of red clover provide a first basis for genomics-assisted breeding.
Abstract
Red clover ( Trifolium pratense L.) is an important forage legume of temperate regions, particularly valued for its high yield potential and its high forage quality. Despite substantial breeding progress during the last decades, continuous improvement of cultivars is crucial to ensure yield stability in view of newly emerging diseases or changing climatic conditions. The high amount of genetic diversity present in red clover ecotypes, landraces, and cultivars provides an invaluable, but often unexploited resource for the improvement of key traits such as yield, quality, and resistance to biotic and abiotic stresses. A collection of 397 red clover accessions was genotyped using a pooled genotyping-by-sequencing approach with 200 plants per accession. Resistance to the two most pertinent diseases in red clover production, southern anthracnose caused by Colletotrichum trifolii , and clover rot caused by Sclerotinia trifoliorum, was assessed using spray inoculation. The mean survival rate for southern anthracnose was 22.9% and the mean resistance index for clover rot was 34.0%. Genome-wide association analysis revealed several loci significantly associated with resistance to southern anthracnose and clover rot. Most of these loci are in coding regions. One quantitative trait locus (QTL) on chromosome 1 explained 16.8% of the variation in resistance to southern anthracnose. For clover rot resistance we found eight QTL, explaining together 80.2% of the total phenotypic variation. The SNPs associated with these QTL provide a promising resource for marker-assisted selection in existing breeding programs, facilitating the development of novel cultivars with increased resistance against two devastating fungal diseases of red clover.
... While the genetic basis of southern anthracnose resistance in red clover is largely unknown, resistance to Colletotrichum spp. has been studied in other legume species including soybean, common bean, and the model species M. truncatula (Ameline-Torregrosa et al. 2008;Yang et al. 2008). ...
... ; https://doi.org/10.1101/2022.05.QTL on LG6 was only found when inoculated with C. trifolii race 1. The QTL on LG4 explained about 40% of the total phenotypic variation and contained a cluster of NLR genes(Ameline-Torregrosa et al. 2008). A single dominant gene named RCT1 on chromosome 4 ...
Red clover ( Trifolium pratense L.) is an important forage legume of temperate regions, particularly valued for its high yield potential and its high forage quality. Despite substantial breeding progress during the last decades, continuous improvement of cultivars is crucial to ensure yield stability in view of newly emerging diseases or changing climatic conditions. The high amount of genetic diversity present in red clover ecotypes, landraces and cultivars provides an invaluable, but often unexploited resource for the improvement of key traits such as yield, quality, and resistance to biotic and abiotic stresses.
A collection of 397 red clover accessions was genotyped using a pooled genotyping-by-sequencing approach with 200 plants per accession. Resistance to the two most pertinent diseases in red clover production, southern anthracnose caused by Colletotrichum trifolii , and clover rot caused by Sclerotinia trifoliorum , was assessed using spray inoculation. The mean survival rate for southern anthracnose was 22.9% and the mean resistance index for clover rot was 34.0%. Genome-wide association analysis revealed several loci significantly associated with resistance to southern anthracnose and clover rot. Most of these loci are in coding regions. One quantitative trait locus (QTL) on chromosome 1 explained 16.8% of the variation in resistance to southern anthracnose. For clover rot resistance we found eight QTL, explaining together 80.2% of the total phenotypic variation. The SNPs associated with these QTL provide, once validated, a promising resource for marker-assisted selection in existing breeding programs, facilitating the development of novel cultivars with increased resistance against two devastating fungal diseases of red clover.
Key message
High variability for and candidate loci associated with resistance to southern anthracnose and clover rot in a worldwide collection of red clover provide a first basis for genomics-assisted breeding.
... Furthermore, the availability of M. truncatula accessions exhibiting varying degrees of resistance against the adapted PM Erysiphe pisi enables the discovery of genetic and molecular determinants of resistance. Genetic studies have previously identified three distinct PM resistance loci (Ameline-Torregrosa et al., 2008) and a resistance gene, MtREP1, that controls PM resistance in the highly resistant M. truncatula genotype Jemalong A17 (Yang et al., 2013). Pathogen growth on A17 is arrested after appressorium development and is associated with the accumulation of hydrogen peroxide and fluorescent compounds at fungal penetration sites, consistent with a hypersensitive response (HR) (Foster-Hartnett et al., 2007;Gupta et al., 2020). ...
Powdery mildew (PM) caused by the obligate biotrophic fungal pathogen Erysiphe pisi is an economically important disease of legumes. Legumes are rich in isoflavonoids, a class of secondary metabolites whose role in PM resistance is ambiguous. Here we show that the pterocarpan medicarpin accumulates at fungal infection sites, as analysed by fluorescein‐tagged medicarpin, and provides penetration and post‐penetration resistance against E. pisi in Medicago truncatula in part through the activation of the salicylic acid (SA) signalling pathway. Comparative gene expression and metabolite analyses revealed an early induction of isoflavonoid biosynthesis and accumulation of the defence phytohormones SA and jasmonic acid (JA) in the highly resistant M. truncatula genotype A17 but not in moderately susceptible R108 in response to PM infection. Pretreatment of R108 leaves with medicarpin increased SA levels, SA‐associated gene expression, and accumulation of hydrogen peroxide at PM infection sites, and reduced fungal penetration and colony formation. Strong parallels in the levels of medicarpin and SA, but not JA, were observed on medicarpin/SA treatment pre‐ or post‐PM infection. Collectively, our results suggest that medicarpin and SA may act in concert to restrict E. pisi growth, providing new insights into the metabolic and signalling pathways required for PM resistance in legumes. Infection‐localized accumulation of the isoflavonoid phytoalexin medicarpin provides resistance against the pea powdery mildew pathogen and activates salicylic acid signalling in Medicago truncatula.
... In 2008, three major QTLs of M. truncatula responsible for different levels of powderymildew resistance were found, namely Epp1 (located on chromosome 4), Epa1 and Epa2 (both located on chromosome 5) [153]. It is worth mentioning that the phenotype of different genetic mechanisms of resistance was the same: E. pisi was not able to penetrate the cell wall of the plant (which suggests the possible involvement of MLO homologs). ...
Grain legumes, or pulses, have many beneficial properties that make them potentially attractive to agriculture. However, the large-scale cultivation of legumes faces a number of difficulties, in particular the vulnerability of the currently available cultivars to various diseases that significantly impair yields and seed quality. One of the most dangerous legume pathogens is powdery mildew (a common name for parasitic fungi of the order Erisyphales). This review examines the methods of controlling powdery mildew that are used in modern practice, including fungicides and biological agents. Special attention is paid to the plant genetic mechanisms of resistance, which are the most durable, universal and environmentally friendly. The most studied legume plant in this regard is the garden pea (Pisum sativum L.), which possesses naturally occurring resistance conferred by mutations in the gene MLO1 (Er1), for which we list here all the known resistant alleles, including er1-12 discovered by the authors of this review. Recent achievements in the genetics of resistance to powdery mildew in other legumes and prospects for the introduction of this resistance into other agriculturally important legume species are also discussed.
... Previous studies (Ameline-Torregrosa et al., 2008;Ben et al., 2013;Djébali et al., 2009;Vailleau et al., 2007;Yang et al., 2008) used RILs populations derived from the cross between M. truncatula accessions for QTL analysis to facilitate the advancement of genetic studies once biodiversity in responses was observed. We assessed the disease caused by F. oxysporum, F. solani, and R. solani to differentiate between the inbred lines based on their resistance level. ...
Fusarium and Rhizoctonia genera are important pathogens of many field crops worldwide. They are constantly evolving and expanding their host range. Selecting resistant cultivars is an effective strategy to break their infection cycles. To this end, we screened a collection of Medicago truncatula accessions against Fusarium oxysporum, Fusarium solani, and Rhizoctonia solani strains isolated from different plant species. Despite the small collection, a biodiversity in the disease response of M. truncatula accessions ranging from resistant phenotypes to highly susceptible ones was observed. A17 showed relative resistance to all fungal strains with the lowest disease incidence and ratings while TN1.11 was among the susceptible accessions. As an initiation of the characterization of resistance mechanisms, the antioxidant enzymes’ activities, at the early stages of infections, were compared between these contrasting accessions. Our results showed an increment of the antioxidant activities within A17 plants in leaves and roots. We also analyzed the responses of a population of recombinant inbred lines derived from the crossing of A17 and TN1.11 to the infection with the same fungal strains. The broad-sense heritability of measured traits ranged from 0.87 to 0.95, from 0.72 to 0.96, and from 0.14 to 0.85 under control, F. oxysporum, and R. solani conditions, respectively. This high estimated heritability underlines the importance of further molecular analysis of the observed resistance to identify selection markers that could be incorporated into a breeding program and thus improving soil-borne pathogens resistance in crops.
... Histological observations and characterization of er2 and Er3 powdery mildew resistance genes in pea showed a pronounced hypersensitive response after the formation of secondary haustoria at 72 HAI [50]. Similarly, in Pisum fulvum and several M. truncatula genotypes, the most effective resistance mechanism against E. pisi also involves a rapid and localized cell death of attacked epidermal cells, either as a rapid reaction against primary appressoria formation or as late-response following colony establishment [21,51,52] In kudzu-P. pachyrhizi early-acting HR, between 24-48 HAI, although initially observed in the penetrated epidermal cell, hypersensitivity extended to epidermal cells surrounding the penetrated epidermal cells and palisade mesophyll cells in proximity [38]. ...
Legume species are recognized for their nutritional benefits and contribution to the sustainability of agricultural systems. However, their production is threatened by biotic constraints with devastating impacts on crop yield. A deep understanding of the molecular and genetic architecture of resistance sources culminating in immunity is critical to assist new biotechnological approaches for plant protection. In this review, the current knowledge regarding the major plant immune system components of grain and forage legumes challenged with obligate airborne biotrophic fungi will be comprehensively evaluated and discussed while identifying future directions of research. To achieve this, we will address the multi-layered defense strategies deployed by legume crops at the biochemical, molecular, and physiological levels, leading to rapid pathogen recognition and carrying the necessary information to sub-cellular components, on-setting a dynamic and organized defense. Emphasis will be given to recent approaches such as the identification of critical components of host decentralized immune response negatively regulated by pathogens while targeting the loss-of-function of susceptibility genes. We conclude that advances in gene expression analysis in both host and pathogen, protocols for effectoromics pipelines, and high-throughput disease phenomics platforms are rapidly leading to a deeper understanding of the intricate host-pathogen interaction, crucial for efficient disease resistance breeding initiatives.
... Incidentally, Ep can infect Mt, and accessions with varying degrees of susceptibility have been used to identify new sources of PM resistance. So far, two resistance QTLs [17], and a dominant resistance gene (MtREP1) have been identified [18]; however, the molecular mechanisms of resistance have not yet been uncovered. ...
... The Mt genotype A17 was previously reported to display complete resistance to various isolates of Ep whereas DZA was reported to be highly susceptible [17,30]. To test the virulence of the Ep isolate Palampur-1, we assessed fungal growth on leaf tissues of both genotypes over the course of infection. ...
Powdery mildew (PM) is a serious fungal disease of legumes. To gain novel insights into PM pathogenesis and host resistance/susceptibility, we used dual RNA-Seq to simultaneously capture host and pathogen transcriptomes at 1 d post-inoculation of resistant and susceptible Medicago truncatula genotypes with the PM Erysiphe pisi (Ep). Differential expression analysis indicates that R-gene mediated resistance against Ep involves extensive transcriptional reprogramming. Functional enrichment of differentially expressed host genes and in silico analysis of co-regulated promoters suggests that amplification of PTI, activation of the JA/ET signaling network, and regulation of growth-defense balance correlate with resistance. In contrast, processes that favor biotrophy, including suppression of defense signaling and programmed cell death, and weaker cell wall defenses are important susceptibility factors. Lastly, Ep effector candidates and genes with known/putative virulence functions were identified, representing a valuable resource that can be leveraged to improve our understanding of legume-PM interactions.
... For instance, the relationship between NBS-LRR proteins and disease resistance has been well established in the Fabaceae by genome-wide association studies and quantitative trait locus analyses, with the role of NBS-LRRs in resistance to anthracnose shown specifically in Phaseolus vulgaris (Chen et al. 2017;Oblessuc et al. 2014;Richard et al. 2018;Wu et al. 2017;Zuiderveen et al. 2016). Anthracnose resistance has been reported in other plants including legume, sorghum, greater yam, tea plant and lupin (Ameline- Torregrosa et al. 2008;Biruma et al. 2012;Saranya et al. 2017;Wang et al. 2016;You et al. 2005). Based on our findings, these backgrounds support our hypothesis that the resistance mechanism depending on the amino acid change in the LRR domain that we have found in watermelon could be applied to other plants, including Cucurbitaceae and Fabaceae. ...
Key message:
A non-synonymous SNP of CC-NBS-LRR was firstly mapped to confer resistance to anthracnose in watermelon. Newly proposed LRR domain harboring the SNP is evolutionary conserved in the Cucurbitaceae and Fabaceae. Anthracnose disease caused by Colletotrichum devastates many plants. Despite the importance of the disease, the mechanisms of resistance against it are poorly understood. Here, we identified a non-synonymous single-nucleotide polymorphism (SNP) located in a leucine-rich repeat domain as a marker for resistance to anthracnose race 1 in watermelon, using a combination of genetic analyses. We validated this SNP in segregating populations and 59 watermelon accessions using high-resolution melting assays and Sanger sequencing. We demonstrated that the resulting arginine-to-lysine substitution is particularly conserved among the Cucurbitaceae and Fabaceae. We identified a conserved motif, IxxLPxSxxxLYNLQTLxL, found in 1007 orthologues/paralogues from 89 plant species, and discovered that residue 18 of this motif could determine resistance to disease caused by external invaders. This study provides a step forward in understanding anthracnose resistance in watermelon, as well as functional and evolutionary insight into leucine-rich repeat proteins.
