Colletotrichum Sublineolum Research Articles

ANTHRACNOSE RESISTANCE GENE2 confers fungal resistance in sorghum.

Sorghum is an important food and feed crop globally; its production is hampered by anthracnose disease caused by the fungal pathogen Colletotrichum sublineola (Cs). Here, we report identification and characterization of ANTHRACNOSE RESISTANCE GENE 2 (ARG2) encoding a nucleotide-binding leucine-rich repeat (NLR) protein that confers race-specific resistance to Cs strains. ARG2 is one of a cluster of several NLR genes initially identified in the sorghum differential line SC328C that is resistant to some Cs strains. This cluster shows structural and copy number variations in different sorghum genotypes. Different sorghum lines carrying independent ARG2 alleles provided the genetic validation for the identity of the ARG2 gene. ARG2 expression is induced by Cs, and chitin induces ARG2 expression in resistant but not in susceptible lines. ARG2-mediated resistance is accompanied by higher expression of defense and secondary metabolite genes at early stages of infection, and anthocyanin and zeatin metabolisms are upregulated in resistant plants. Interestingly, ARG2 localizes to the plasma membrane when transiently expressed in Nicotiana benthamiana. Importantly, ARG2 plants produced higher shoot dry matter than near-isogenic lines carrying the susceptible allele suggesting an absence of an ARG2 associated growth trade-off. Furthermore, ARG2-mediated resistance is stable at a wide range of temperatures. Our observations open avenues for resistance breeding and for dissecting mechanisms of resistance.

Emulsifying Properties of Rhamnolipids and Their In Vitro Antifungal Activity against Plant Pathogenic Fungi.

Rhamnolipids have significant emulsifying activity and the potential to become a component of pesticide emulsifier. Rhamnolipids are usually composed of two main components: mono-rhamnolipids (Rha-C10-C10) and di-rhamnolipids (Rha2-C10-C10). The proportion of di-rhamnolipids in the products ranged between 15% and 90%, affected by the production strains and fermentation process. In this paper, three kinds of rhamnolipid products containing di-rhamnolipids proportions, of 25.45, 46.46 and 89.52%, were used to test their emulsifying ability toward three conventional solvents used in pesticide (S-200, xylene, cyclohexanone) and antifungal activities against five strains of plant pathogenic fungi (Phytophthora capsici, Phytophthora parasitica var.nicotianae, Colletotrichum destructivum, Colletotrichum sublineolum, Fusarium oxysporum). The results indicated that although the CMC of the three rhamnolipids were significantly different, their emulsification properties had no remarkable differences, at a concentration of 10 g/L. However, their antifungal activities were significantly different: the more di-rhamnolipids, the stronger the antifungal activity. This work helps to promote the application of rhamnolipids as pesticides adjuvants.

Survey of Fungal Foliar and Panicle Diseases in Smallholder Sorghum Cropping Systems in Different Agro-Ecologies of Lower Eastern Kenya

Sorghum is a staple food crop and plays a critical role in subsistence farming in Kenya due to its adaptability to marginal agro-ecological zones. However, fungal diseases are among the major biotic constraints of sorghum production, causing over 70% yield loss in susceptible cultivars. Information on the distribution and severity of fungal diseases is important to establish efficient and improved strategies for integrated disease management of sorghum fungal diseases. The aim of this study was to determine the prevalence, incidence, severity and spatial distribution of fungal diseases on sorghum across agro-ecological zones of lower eastern Kenya. A total of 384 smallholder farmers’ fields were surveyed, and in each field, 30 plants were assessed for prevalence and incidence of fungal diseases using a W-shaped pattern to cover the whole field. Sorghum anthracnose was the most prevalent disease (71%), followed by leaf blight (70.18%), rust (68.41%), smut (63.02%), sorghum mildew (55.33%), Alternaria leaf spot (48.39%) and rough leaf spot (46.02%). Disease prevalence, incidence and severity varied among the investigated agro-ecological zones. There was a significant difference (p ≤ 0.05) in fungal disease severity across the investigated agro-ecological zones. Spatially interpolated disease maps showed a high variation in the distribution of various sorghum fungal diseases across the investigated agro-ecological zones of lower eastern Kenya. Morpho-cultural identification revealed the association of Colletotrichum sublineola with anthracnose, Curvularia lunata and Bipolaris cynodontis with leaf blight, Puccinia purpurea with rust, Peronosclerospora sorghi with downy mildew, Alternaria alternata with Alternaria leaf spot, Ascochyta sorghi with rough leaf spot and Sporisorium sorghi with covered kernel smut symptoms. Information obtained in this study will be useful to update knowledge on sorghum fungal diseases and provide a basis for the development of strategies for management and control of the investigated diseases.

Genome-wide association study of Senegalese sorghum seedlings responding to a Texas isolate of Colletotrichum sublineola

Colletotrichum sublineola is a destructive fungal pathogen that causes anthracnose in sorghum. Senegalese sorghum germplasm is currently being considered as an option of sources for genetic resistance. In a recent study, Senegalese sorghum accessions were evaluated for response to a mixture of Texas isolates of C. sublineola at the 8-leaf stage in the greenhouse. As a comparison, 159 Senegalese sorghum accessions at the 1-leaf developmental stage were evaluated against a single Texas isolate of C. sublineola (FSP53) using an excised-leaf assay. A genome-wide association study (GWAS) was conducted based on the phenotypic data acquired to discover genetic variation associated with response to C. sublineola using 193,727 single nucleotide polymorphisms (SNPs) throughout the genome. Sorghum seedlings tended to be more resistant when compared with sorghum plants inoculated at the 8-leaf stage in the greenhouse in previous experiments. Based on the highest score evaluated in the 1-leaf developmental stage excised leaf assay for each accession, 16 accessions were labeled as susceptible. GWAS identified the SNP locus S01_72868925 that is associated with protein kinase domain // Leucine rich repeat N-terminal domain at a level of confidence that surpassed Bonferroni correction. Along with the SNP locus S01_72868925, other top SNP loci were also associated with genes that are known to play critical roles in plant defense or plant stress responses.

Johnsongrass rhizome tissue can be infected by Colletotrichum sublineola

Four isolates of Colletotrichum sublineola were inoculated on excised leaf blades and rhizomes of nine Johnsongrass accessions and leaf blades of two sorghum accessions, BTx623 (+) and SC748-5 (−). Successful acervuli formations were observed in seven Johnsongrass accession-C. sublineola isolate combinations. Although infection leading to pathogen reproduction was rarely observed, this is the first study that confirmed Johnsongrass rhizomes can be colonized by C. sublineola.

Genetic mapping of sorghum resistance to an Illinois isolate of Colletotrichum sublineola.

Anthracnose leaf blight (ALB) is an economically important disease of sorghum [Sorghum bicolor (L.) Moench] caused by the fungal pathogen Colletotrichum sublineola Henn. ex Sacc. & Trotter. Although qualitative and quantitative resistance have been identified for ALB, the usefulness of resistance loci differs depending on the pathogen pathotype. Identifying resistance effective against unique pathogen pathotypes is critical to managing ALB, as the disease is managed primarily through the deployment of host resistance. We isolated C. sublineola from ALB-infected leaves collected in Illinois and found that the strain was a novel pathotype, as it produced a unique combination of virulence against a set of differential lines. Using this isolate, we inoculated 579 temperate-adapted sorghum conversion lines in 2019 and 2020. We then conducted a genome-wide association study (GWAS) and a metabolic pathway analysis using the Pathway Associated Study Tool (PAST). We identified 47 significant markers distributed across all chromosomes except chromosome 8. We identified 32 candidate genes based on physical proximity with significant markers, some of which have a known role in host defense. We identified 47 pathways associated with ALB resistance, indicating a role for secondary metabolism in defense to ALB. Our results are important to improve the understanding of the genetic basis of ALB resistance in sorghum and highlight the importance of developing durable resistance to ALB.

Transcriptome analysis provides insights into the bases of salicylic acid-induced resistance to anthracnose in sorghum.

Key Message Transcriptome analysis of SA sensitive and tolerant lines indicates that SA enhances anthracnose resistance in sorghum by upregulating the expression of some immune-related genes and pathways.Abstract Anthracnose caused by the hemibiotrophic pathogen Colletotrichum sublineolum is one of the most destructive diseases of sorghum, the fifth most important cereal crop in the world. Salicylic acid (SA) is a phytohormone essential for plant immunity; however, the role of SA in sorghum resistance to anthracnose has not been well explored. In this study, we found that Colletotrichum sublineolum infection induced the expression of SA-responsive genes and that exogenous SA enhanced resistance to anthracnose in the sorghum line BTx623. To rule out the possibility that SA triggers anthracnose resistance in sorghum by its direct toxic function on pathogen, an SA-tolerant line, WHEATLAND, was identified, and we found that SA treatment could not induce anthracnose resistance in WHEATLAND. Then, SA-induced transcriptome changes during Colletotrichum sublineolum infection in BTx623 and WHEATLAND were analyzed to explore the molecular mechanism of SA-triggered resistance. SA pretreatment regulated the expression of 2125 genes in BTx623 but only 524 genes in WHEATLAND during Colletotrichum sublineolum infection. The cutin, suberine and wax biosynthesis pathway involved in the plant immune response and the flavonoid biosynthesis pathway involved in anthracnose resistance were enriched in BTx623-specifically upregulated genes. Additionally, some immune-related genes, including multiple resistance genes, were differentially expressed in BTx623 and WHEATLAND. Taken together, our results revealed the mechanisms of SA-induced anthracnose resistance in sorghum at the transcriptional level and shed light on the possibility of enhancing sorghum resistance to anthracnose by activating the SA signaling pathway by molecular breeding.

Exploring the integrated use of fungicides, bio-control agent and biopesticide for management of foliar diseases (anthracnose, grey leaf spot and zonate leaf spot) of sorghum

Foliar diseases of sorghum (Sorghum bicolor) such as anthracnose (Colletotrichum sublineolum), grey leaf spot (Cercospora sorghi) and zonate leaf spot (Gloeocercospora sorghi), are major biotic constraints to forage and grain production globally. Therefore, a study was undertaken to exploit the potential of the biocontrol agent Trichoderma, botanical biopesticide Neem extract and fungicides carbendazim and propiconazole in an integrated manner against foliar pathogens of sorghum in factorial randomized complete block design in two geographically different locations [Ludhiana (Punjab) and Palampur (Himachal Pradesh)] of India during four years (2016–2019). The lowest severity of anthracnose and grey leaf spot with corresponding disease control of 48.9% and 42.4% was recorded with seed dressing of carbendazim followed by one spray each with neem biopesticide and propiconazole at 20 and 35 days after sowing with 43.1% increase in green fodder yield. For zonate leaf spot, seed dressing with carbendazim and two foliar applications of propiconazole showed the lowest disease severity with 82.8% disease control. Thus, the integrated use of neem biopesticide and fungicide will efficiently minimize the severity of sorghum foliar diseases and increase the green fodder yield.

Broad-spectrum fungal resistance in sorghum is conferred through the complex regulation of an immune receptor gene embedded in a natural antisense transcript.

Sorghum (Sorghum bicolor), the fifth most widely grown cereal crop globally, provides food security for millions of people. Anthracnose caused by the fungus Colletotrichum sublineola is a major disease of sorghum worldwide. We discovered a major fungal resistance locus in sorghum composed of the nucleotide-binding leucine-rich repeat receptor gene ANTHRACNOSE RESISTANCE GENE1 (ARG1) that is completely nested in an intron of a cis-natural antisense transcript (NAT) gene designated CARRIER OF ARG1 (CARG). Susceptible genotypes express CARG and two alternatively spliced ARG1 transcripts encoding truncated proteins lacking the leucine-rich repeat domains. In resistant genotypes, elevated expression of an intact allele of ARG1, attributed to the loss of CARG transcription and the presence of miniature inverted-repeat transposable element sequences, resulted in broad-spectrum resistance to fungal pathogens with distinct virulence strategies. Increased ARG1 expression in resistant genotypes is also associated with higher histone H3K4 and H3K36 methylation. In susceptible genotypes, lower ARG1 expression is associated with reduced H3K4 and H3K36 methylation and increased expression of NATs of CARG. The repressive chromatin state associated with H3K9me2 is low in CARG-expressing genotypes within the CARG exon and higher in genotypes with low CARG expression. Thus, ARG1 is regulated by multiple mechanisms and confers broad-spectrum, strong resistance to fungal pathogens.

Evaluation of a Subset of Ethiopia Sorghum Collection Germplasm from the National Genetic Resources Program of the United States Department of Agriculture for Anthracnose Resistance

Globally, one of the most devastating diseases of sorghum is anthracnose incited by Colletotrichum sublineola. During the 2019 and 2020 growing seasons, 94 and 64 accessions from the Ethiopian sorghum germplasm collection maintained by the National Genetic Resources Program of the United States Department of Agriculture were evaluated for anthracnose resistance. Seeds were planted in 1.8 m rows with 0.9 m row spacing in a randomized complete block design. The accessions and checks were replicated three times and 30 days after planting, inoculated by placing C. sublineola-colonized grains in the plant whorls. A total of 30 accessions, including PI533918, PI533923, PI534131 and PI534151 were resistant to the disease in both years. These identified resistant sources can be used in breeding programs to develop anthracnose-resistant lines and hybrids.

Cultural and Morphological Characteristics of Colletotrichum Sublineolum Isolates Infecting Sorghum in Eastern Ethiopia

Cultural and Morphological Characteristics of Colletotrichum Sublineolum Isolates Infecting Sorghum in Eastern Ethiopia

Genome-wide association analysis of anthracnose resistance in sorghum [Sorghum bicolor (L.) Moench

In warm-humid ago-ecologies of the world, sorghum [Sorghum bicolor (L.) Moench] production is severely affected by anthracnose disease caused by Colletotrichum sublineolum Henn. New sources of anthracnose resistance should be identified to introgress novel genes into susceptible varieties in resistance breeding programs. The objective of this study was to determine genome-wide association of Diversity Arrays Technology Sequencing (DArTseq) based single nucleotide polymorphisms (SNP) markers and anthracnose resistance genes in diverse sorghum populations for resistance breeding. Three hundred sixty-six sorghum populations were assessed for anthracnose resistance in three seasons in western Ethiopia using artificial inoculation. Data on anthracnose severity and the relative area under the disease progress curve were computed. Furthermore, the test populations were genotyped using SNP markers with DArTseq protocol. Population structure analysis and genome-wide association mapping were undertaken based on 11,643 SNPs with <10% missing data. The evaluated population was grouped into eight distinct genetic clusters. A total of eight significant (P < 0.001) marker-trait associations (MTAs) were detected, explaining 4.86-15.9% of the phenotypic variation for anthracnose resistance. Out of which the four markers were above the cutoff point. The significant MTAs in the assessed sorghum population are useful for marker-assisted selection (MAS) in anthracnose resistance breeding programs and for gene and quantitative trait loci (QTL) mapping.

Diversity and frequency of fungal genera from sorghum lines inoculated with Alternaria alternata alone and in combination with Curvularia lunata and Fusarium thapsinum in a field infected with anthracnose

Sorghum grain mold is a disease associated with number of fungal genera. In this study, mycoflora analysis of seeds obtained from 91 accessions, including those from the sorghum association panel was conducted. Accessions were inoculated with A. alternata alone, mixture of A. alternata, F. thapsinum, and C. lunata, and water-sprayed control during two growing seasons. Alternaria alternata alone treatment showed Colletotrichum sublineola was the most recovered fungal species followed by A. alternata, and Fusarium spp. Seeds from panicles inoculated with a mixture of A. alternata, F. thapsinum, and C. lunata revealed F. thapsinum, followed by C. lunata, C. sublineola and A. alternata as the most frequently isolated species. In the control treatment, A. alternata and C. sublineola were the most frequently recovered fungal species. Fusarium proliferatum, Aspergillus flavus, A. niger, F. chlamydposporum, F. verticillioides, Rhizopus spp., and Penicillium spp. were also recovered but in low percentages. Due to the large number of fungi associated with the disease, management can be challenging. Studies like this allows for the identification of other grain mold fungi infecting or contaminating sorghum grain in a field. Thus, using those fungi species in a particular region, either individually or in combination to screen germplasm for resistance or tolerance to this disease complex is recommended. Keywords: Mycoflora, Sorghum, Grain Mold, Fungal Species, Alternaria alternata, Fusarium thapsinum, Curvularia lunata

Effect of Leaf Age, Leaf Segments and Surface Treatments on Pathogenicity Levels of Colletotrichum sublineola in Sorghum and Johnson Grass

Colletotrichum sublineola is a casual pathogen of sorghum anthracnose. Sorghum pathologists often need to conduct evaluations for anthracnose resistance in large scale which are expensive and labor intensive. As a solution, an excised-leaf assay has been used, but whether or not leaf age, position or region affects pathogenicity scores has not previously been evaluated. Essentially, in an excised-leaf assay, is response to C. sublineola over all or part of a leaf blade identical? To get an answer, three sorghum and one Johnson grass cultivars were tested. The top five leaves were inoculated at the apex, mid-leaf and base of each leaf blade. Results show nearly no effect of leaf age to pathogenicity level within the top five leaves. Furthermore, in order to evaluate any protective role of leaf wax to C. sublineola, the wax was disrupted by simply wiping the leaf surface by a thumb, or as an alternative method, leaf surface tension was reduced by submerging leaves into 2% TWEEN 20 before inoculation. Compared to control, wiped leaves increased pathogenicity scores on the leaf blade and midrib in two of three sorghum cultivars, but 2% TWEEN 20-treated leaves had only minimal changes in pathogenicity level compared to controls.

Pathogenic variability of Colletotrichum sublineolum isolates on sorghum differentials under greenhouse conditions in Jimma, Ethiopia

Sorghum anthracnose caused by Colletotrichum sublineolum is one of the most destructive diseases affecting sorghum production in Ethiopia. Pathogenic variability of C. sublineolum isolates on some sorghum differentials under greenhouse condition was evaluated in Jimma, Ethiopia. Highly significant (P < 0.001) differences among sorghum differentials, C. sublineolum isolates and their interactions on incubation period, aggressiveness, virulence index, virulence, the first and final anthracnose severity assessments, disease infection rate and AUDPC were studied. Among the interactions, the interaction between CsAs7 (isolate from Assosa zone field 7) and sorghum differentials had the shortest mean incubation period (3.5 days), highest first and final anthracnose severity, highest virulence index, fastest disease infection rate and highest AUDPC as compared to others. This isolate showed the most aggressive and virulent reaction than others followed by CsJm5. The interaction of PI570726 and SC748-5 sorghum differentials and all C. sublineolum isolates produce 100 and 80% resistant reactions, respectively and they could be used as good sources of resistance genes for breeding programs for sorghum anthracnose management.

The inheritance of anthracnose (Colletotrichum sublineola) resistance in sorghum differential lines QL3 and IS18760

Anthracnose caused by the fungal pathogen C. sublineola is an economically important constraint on worldwide sorghum production. The most effective strategy to safeguard yield is through the introgression of resistance alleles. This requires elucidation of the genetic basis of the different resistance sources that have been identified. In this study, 223 recombinant inbred lines (RILs) derived from crossing anthracnose-differentials QL3 (96 RILs) and IS18760 (127 RILs) with the common susceptible parent PI609251 were evaluated at four field locations in the United States (Florida, Georgia, Texas, and Puerto Rico) for their anthracnose resistance response. Both RIL populations were highly susceptible to anthracnose in Florida and Georgia, while in Puerto Rico and Texas they were segregating for anthracnose resistance response. A genome scan using a composite linkage map of 982 single nucleotide polymorphisms (SNPs) detected two genomic regions of 4.31 and 0.85 Mb on chromosomes 4 and 8, respectively, that explained 10–27% of the phenotypic variation in Texas and Puerto Rico. In parallel, a subset of 43 RILs that contained 67% of the recombination events were evaluated against anthracnose pathotypes from Arkansas (2), Puerto Rico (2) and Texas (4) in the greenhouse. A genome scan showed that the 7.57 Mb region at the distal end of the short arm of chromosome 5 is associated with the resistance response against the pathotype AMP-048 from Arkansas. Comparative analysis identified the genomic region on chromosome 4 overlaps with an anthracnose resistance locus identified in another anthracnose-differential line, SC414-12E, indicating this genomic region is of interest for introgression in susceptible sorghum germplasm. Candidate gene analysis for the resistance locus on chromosome 5 identified an R-gene cluster that has high similarity to another R-gene cluster associated with anthracnose resistance on chromosome 9.

Genome Assembly and Transcriptome of Colletotrichum sublineola CsGL1, a New Resource to Study Anthracnose Disease in Sorghum.

Colletotrichum species are globally distributed and well known as members of a destructive phytopathogenic genus, causing the anthracnose disease in a wide variety of crops and fruits. Colletotrichum sublineola is the causal agent of the anthracnose disease in sorghum, causing losses of up to 50% in yield. Here, we used PacBio sequencing combined with RNA-seq to generate a chromosome-level assembly and annotation of the Colletotrichum sublineola strain CsGL1.[Formula: see text] Copyright © 2021 The Author(s). This is an open access article distributed under the CC BY-NC-ND 4.0 International license.

Major Sorghum Production Constraints and Coping Mechanisms: The Case of Anthracnose (Colletotrichum sublineolum)

This paper attempts to review the major sorghum production constraints, the progress and perspective on sorghum anthracnose (Colletotrichum sublineolum) resistance breeding. The importance of anthracnose in sorghum production and breeding for resistance status and progress were also primly discovered. Sorghum is an ancient environment resilient crop and believed to be a future crop due to its important merits like tolerant to stresses, wide adaptability and low input requirement. Insects and disease are major biotic impediments to realizing the yield potential of the crop. Anthracnose disease caused by Colletotrichum sublineolum is the most important disease that severely affecting the crop in all sorghum producing regions of the world. Research results revealed that anthracnose resulted in 30-50% or greater yield losses. Several management strategies such as, cultural, chemical and using resistance varieties have been developed. Employing host-plant resistance is the most economical and environmentally friendly approach which can successfully control the disease. Breeding assisted with molecular markers plays a great role in resistance breeding programme as it makes easy to screen large number of genotypes at once. Recent advancement of molecular breeding and bio-informatics tools are playing a significant role in efficiencies and precisions of resistance breeding. QTLs or genomic area for resistance were identified using traditional molecular markers and recent research results revealed discoveries of specific gene and locus using high throughput markers like SNPs using GWAS approach. The discovery of genes/QTL associated with the resistance trait, using the high through put molecular markers like SNPs, facilitates the easiest way for gene pyramiding from different individual genotypes to a single variety, introgression into adapted elite cultivar through marker assisted and editing genes for elite landraces to develop durable resistance varieties. Transgenic approach is now a day becoming a powerful tool to utilize novel alien genes for crop improvement including anthracnose resistance breeding in sorghum.

RNA-Sequencing in Resistant (QL3) and Susceptible (Theis) Sorghum Cultivars Inoculated With Johnsongrass Isolates of Colletotrichum sublineola.

Gene expression was analyzed at 0- and 24-h post-inoculation of two inbred sorghum cultivars known to differ in response to inoculation with Colletotrichum sublineola, the fungal pathogen that causes anthracnose. QL3 is reported to have quantitative resistance, while Theis is susceptible to most pathotypes of the pathogen; RNASeq identified over 3,000 specific genes in both cultivars as showing significant changes in expression following inoculation; in all but one gene, the changes in QL3 and Thies were in the same direction. Many other genes showed significant changes in only one of the two cultivars. Overall, more genes were downregulated than upregulated. Differences in changes in expression levels of a few genes suggested potential roles for the difference in disease response between QL3 and Theis, but did not identify known resistance genes. Gene ontology (GO) and pathway enrichment analysis identified upregulation of 23 transcription factor encoding genes as well as genes involved in the production of secondary metabolites, which are part of a typical host defense reaction.

The response of sorghum cultivars to mixtures of compatible and incompatible isolates and different conidia concentrations of Colletotrichum sublineola

The anthracnose pathogen Colletotrichum sublineola and its sorghum host provide an excellent system to examine concepts associated with gene-for-gene resistance. In this study, an excised-leaf spot inoculation assay method was used to evaluate host-pathogen interactions across several sorghum cultivars that serve as host differentials for defining races of the pathogen. Host cultivars tested included sorghum cultivars BTx398, RTx2536, Theis and johnsongrass cultivar SH1152. The cultivars were inoculated at varying conidia concentrations both singly and in pairs with conidia from strains of C. sublineola that differ in ability to incite the disease anthracnose. The hypothesis tested was that host defense triggered by effectors produced by an avirulent strain will limit infection when simultaneously inoculated with a strain that otherwise would lead to disease. Observations revealed significant changes in disease ratings based on conidial concentrations of the C. sublineola isolates used. However, disease rating scores for combined inocula in the excised-leaf spot inoculation assays led to scores either between the scores generated by single isolates or near the score of the more virulent isolate.