First report of Colletotrichum scovillei causing anthracnose fruit rot of pepper in Ohio

In August 2019, the Ohio State University Vegetable Pathology laboratory received multiple bell and banana pepper fruits (Capsicum annuum, cvs. unknown) from Columbiana County, Ohio. The grower reported a disease incidence of 100% and severity of 70% in fruits across their pepper fields. Fruit lesions were brown, sunken, and covered with orange-colored sporulation. On banana peppers, the lesions mainly affected the blossom end of the fruits, while the lesions were distributed randomly on bell pepper fruits. Pieces of diseased tissue were cut from the fruit and surface sterilized in 0.5-0.6 % sodium hypochlorite, rinsed in sterile water, blotted dry, and placed on potato dextrose agar. All of the fungal cultures recovered were cottony, pale gray-green with shades of orange on the underside of the mycelial mat. Two representative isolates, SM209-19 (bell pepper) and SM210-19 (banana pepper), were grown on oatmeal agar to induce sporulation. Pink-orange concentric rings containing acervuli and conidia were present on the oatmeal agar plates after one week of growth at 22◦C (12-h dark/light). Conidia (n=29) were hyaline, aseptate, cylindrical in shape, and had an average length of 10.5 µm (std. dev. = 1.3 µm) and width of 4.1 µm (std. dev. = 0.6 µm) (Fig.1). DNA was extracted from both isolates using a DNeasy Plant Kit (Qiagen Inc, Germantown, MD), and partial sequences of the internal transcribed spacer (ITS) region, -tubulin 2 gene (TUB2), and glyceraldehyde-3-phosphate dehydrogenase gene (GDPH) were amplified by PCR with the following primers: ITS4/ITS5 (White et al. 1990), Bt1a/Bt1b (Glass et al. 1995), and GDF1/GDR1 (Guerber et al. 2003), and squenced. The ITS region of both isolates SM209-19 and SM210-19 (PP280815 and PP280816, respectively) showed 100% identity with C. scovillei (Cs) isolate LJTJ35 (KP748226). The partial sequences of GDPH, (PP320348, PP320349, respectively) showed 99% sequence identity with the Cs CBS 126528 (JQ948597) and 100% identity with Cs HP1 (MT826948) The partial sequences of TUB2 (PP472464 and PP472465, respectively) had 100% sequence similarity with the Cs HP1 and Cs CBS 126528 (MT826951, JQ949918 respectively). Pathogenicity was tested in a greenhouse experiment on blossoming bell pepper plants (cv. Carmen) by spraying 10 ml of 1 X 105 conidia/ml suspension onto flower blooms (nine plants per isolate). Control pepper plants were mock inoculated by spraying 10 mL of sterile deionized water. The plants were re-inoculated one week later. Brown, sunken lesions with orange sporulation developed on the fruits of inoculated plants 21 days after the initial inoculation (Fig. 2), while the mock-inoculated plants did not produce any symptoms. Culturing from symptomatic fruits on PDA, following the same method described above, produced fungal colonies with the same morphological traits previously described. C. scovillei causing anthracnose on pepper has been described in the US (Toporek et al. 2021), Brazil (Caires et al. 2014), China (Zhao et al. 2016), and different South Asia Countries (Khalimi et al. 2019). Open-field peppers are produced in Ohio on more than 5,400 acres, with a value of more than $53 million, with anthracnose being one of the most severe fungal diseases reducing yield. This newly reported Colletotichum species could represent a further threat for this crop. Further studies evaluating fungicide sensitivity and efficacy against this pathogen will be of crucial importance for disease management.

Expression of Genes Involved in Anthracnose Resistance in Chili (Capsicum baccatum) 'PBC80'-Derived Recombinant Inbred Lines

Chili anthracnose has long been a threat to chili production worldwide. Capsicum baccatum 'PBC80' has been identified as a source of resistance to anthracnose. Recently, a QTL for ripe fruit resistance from 'PBC80'-derived RILs was located on chromosome 4 (123 Mb) and contained over 80 defense-related genes. To identify the genes most related to anthracnose resistance, a fine map of the QTL region was developed using single-marker analysis. Nine genes were selected from the new QTL (1.12 Mb) to study their expression after being challenged with Colletotrichum scovillei 'MJ5' in two different RIL genotypes (Resistance/Resistance or R/R and Susceptible/Susceptible or S/S) at 0, 6 and 12 h. Of the nine genes, LYM2, CQW23_09597, CLF, NFXL1, and PR-14 were significantly up-regulated, compared to the control, in the R/R genotype. ERF was up-regulated in both chili genotypes. However, the expression was relatively and constantly low in the S/S genotype. Most up-regulated genes reached the highest peak (2.3-4.5 fold) at 6 h, except for ERF, which had the highest peak at 12 h (6.4 fold). The earliest and highest expressed gene was a pathogen receptor, LYM2.

Resistance risk and resistance-related point mutations in cytochrome b of florylpicoxamid in Colletotrichum scovillei

Anthracnose caused by Colletotrichum scovillei is one of the most destructive diseases of chili worldwide. Florylpicoxamid is a new quinone inside inhibitor (QiI) fungicide, which shows intensively inhibitory activity against C. scovillei. Currently, florylpicoxamid is in the registration process to control chili anthracnose in China. This study investigated the risk of resistance and resistance genetic mechanism of C. scovillei to florylpicoxamid. Baseline sensitivity of 141C. scovillei isolates to florylpicoxamid was established with an average EC50 value of 0.2328 ± 0.0876 μg/mL. A total of seven stable florylpicoxamid-resistant mutants were obtained with resistance factors ranging from 41 to 276. The mutants showed similar or weaker traits in mycelial growth, sporulation, conidial germination and pathogenicity than their parental isolates. Generally, the resistance risk of C. scovillei to florylpicoxamid would be moderate. In addition, there was no cross-resistance between florylpicoxamid and the commercially available fungicides tested. A37V and S207L mutations in the cytochrome b protein were detected in four high-resistance and three moderate-resistance mutants, respectively, of which, S207L is a new mutation. Molecular docking showed that the two mutations conferred different resistance levels to florylpicoxamid. These results provide a new perspective for QiI fungicide-resistance mechanism and may help in the reasonable use of florylpicoxamid against chili anthracnose in the future.

Application of Essential Oils Extracted from Peel Wastes of Four Orange Varieties to Control Anthracnose Caused by Colletotrichum scovillei and Colletotrichum gloeosporioides on Mangoes

A huge amount of orange peel waste is annually discharged into the environment. Processing of this waste for the control of post-harvest fruit diseases can reduce environmental pollution. Essential oils (EOs) from fruit peels of Citrus reticulata × sinensis (Sanh cultivar) and Citrus sinensis (Xoan, Mat and Navel cultivar) were investigated for their ability to control anthracnose caused by Colletotrichum gloeosporioides and Colletotrichum scovillei on mangoes. EOs were extracted by hydro-distillation and analyzed by GC-MS and GC-FID. The antifungal activity of the EOs was determined by in vitro and in vivo assays. The Mat cultivar had the highest extraction yield of 3% FW, followed by Xoan (2.9%), Sanh (2.2%), and Navel (1%). The chemical composition of the EOs was similar, with limonene as the main compound (around 96%). The antifungal activity of EOs was not different, with a minimum fungicidal concentration of 16% for both fungi. The disease inhibition of EOs increased with their concentration. The highest inhibition of anthracnose caused by both fungi on mangoes was achieved at 16% EO. EOs had no adverse effect on mango quality (pH, total soluble solids, total acidity, color and brightness of mangoes), except firmness and weight loss at high concentrations (16%). Orange EOs can be used as bio-fungicides to control mango anthracnose at high concentrations.

The Cell Wall Integrity MAP Kinase Signaling Pathway Is Required for Development, Pathogenicity, and Stress Adaption of the Pepper Anthracnose Fungus Colletotrichum scovillei

The cell wall integrity (CWI) signaling pathway plays important roles in the dissemination and infection of several plant pathogenic fungi. However, its roles in the pepper fruit anthracnose fungus Colletotrichum scovillei remain uninvestigated. In this study, the major components of the CWI signaling pathway-CsMCK1 (MAPKKK), CsMKK1 (MAPKK), and CsMPS1 (MAPK)-were functionally characterized in C. scovillei via homology-dependent gene replacement. The ΔCsmck1, ΔCsmkk1, and ΔCsmps1 mutants showed impairments in fungal growth, conidiation, and tolerance to CWI and salt stresses. Moreover, ΔCsmck1, ΔCsmkk1, and ΔCsmps1 failed to develop anthracnose disease on pepper fruits due to defects in appressorium formation and invasive hyphae growth. These results suggest that CsMCK1, CsMKK1, and CsMPS1 play important roles in mycelial growth, conidiation, appressorium formation, plant infection, and stress adaption of C. scovillei. These findings will contribute to a better understanding of the roles of the CWI signaling pathway in the development of pepper fruit anthracnose disease.

CaWRKY50 Acts as a Negative Regulator in Response to Colletotrichum scovillei Infection in Pepper

Chili anthracnose is one of the most common and destructive fungal pathogens that affects the yield and quality of pepper. Although WRKY proteins play crucial roles in pepper resistance to a variety of pathogens, the mechanism of their resistance to anthracnose is still unknown. In this study, we found that CaWRKY50 expression was obviously induced by Colletotrichum scovillei infection and salicylic acid (SA) treatments. CaWRKY50-silencing enhanced pepper resistance to C. scovillei, while transient overexpression of CaWRKY50 in pepper increased susceptibility to C. scovillei. We further found that overexpression of CaWRKY50 in tomatoes significantly decreased resistance to C. scovillei by SA and reactive oxygen species (ROS) signaling pathways. Moreover, CaWRKY50 suppressed the expression of two SA-related genes, CaEDS1 (enhanced disease susceptibility 1) and CaSAMT1 (salicylate carboxymethyltransferase 1), by directly binding to the W-box motif in their promoters. Additionally, we demonstrated that CaWRKY50 interacts with CaWRKY42 and CaMIEL1 in the nucleus. Thus, our findings revealed that CaWRKY50 plays a negative role in pepper resistance to C. scovillei through the SA-mediated signaling pathway and the antioxidant defense system. These results provide a theoretical foundation for molecular breeding of pepper varieties resistant to anthracnose.

Exploring the Potentiality of Native Actinobacteria to Combat the Chilli Fruit Rot Pathogens under Post-Harvest Pathosystem

Chilli is an universal spice cum solanaceous vegetable crop rich in vitamin A, vitamin C, capsaicin and capsanthin. Its cultivation is highly threatened by fruit rot disease which cause yield loss as high as 80-100% under congenial environment conditions. Currently actinobacteria are considered as eco-friendly alternatives to synthetic fungicides at pre and post-harvest pathosystems. Hence, this research work focuses on the exploitation of rhizospheric, phyllospheric and endophytic actinobacteria associated with chilli plants for their antagonistic activity against fruit rot pathogens viz., Colletotrichum scovillei, Colletotrichum truncatum and Fusarium oxysporum. In vitro bioassays revealed that the actinobacterial isolate AR26 was found to be the most potent antagonist with multifarious biocontrol mechanisms such as production of volatile, non-volatile, thermostable compounds, siderophores, extracellular lytic enzymes. 16S rRNA gene sequence confirmed that the isolate AR26 belongs to Streptomyces tuirus. The results of detached fruit assay revealed that application of liquid bio-formulation of Stretomyces tuirus @ 10 mL/L concentration completely inhibited the development of fruit rot symptoms in pepper fruits compared to methanol extracts. Hence, the present research work have a great scope for evaluating the biocontrol potential of native S. tuirus AR26 against chilli fruit rot disease under field condition as well against a broad spectrum of post-harvest plant pathogens.

The Autophagy Protein CsATG8 is Involved in Asexual Development and Virulence in the Pepper Anthracnose Fungus Colletotrichum scovillei

Autophagy serves as a survival mechanism and plays important role in nutrient recycling under conditions of starvation, nutrient storage, ad differentiation of plant pathogenic fungi. However, autophagy-related genes have not been investigated in Colletotrichum scovillei, a causal agent of pepper fruit anthracnose disease. ATG8 is involved in autophagosome formation and is considered a marker of autophagy. Therefore, we generated an ATG8 deletion mutant, ΔCsatg8, via homologous recombination to determine the functional roles of CsATG8 in the development and virulence of C. scovillei. Compared with the wild-type, the deletion mutant ΔCsatg8 exhibited a severe reduction in conidiation. Conidia produced by ΔCsatg8 were defective in survival, conidial germination, and appressorium formation. Moreover, conidia of ΔCsatg8 showed reduced lipid amount and PTS1 selectivity. A virulence assay showed that anthracnose development on pepper fruits was reduced in ΔCsatg8. Taken together, our results suggest that CsATG8 plays various roles in conidium production and associated development, and virulence in C. scovillei.

The CsSTE50 Adaptor Protein in Mitogen-Activated Protein Kinase Cascades Is Essential for Pepper Anthracnose Disease of Colletotrichum scovillei

Anthracnose, caused by the ascomycete fungus Colletotrichum scovillei, is a destructive disease in pepper. The fungus germinates and develops an infection structure called an appressorium on the plant surface. Several signaling cascades, including cAMP-mediated signaling and mitogen-activated protein kinase (MAPK) cascades, are involved in fungal development and pathogenicity in plant pathogenic fungi, but this has not been well studied in the fruit-infecting fungus C. scovillei. Ste50 is an adaptor protein interacting with multiple upstream components to activate the MAPK cascades. Here, we characterized the CsSTE50 gene of C. scovillei, a homolog of Magnaporthe oryzae MST50 that functions in MAPK cascades, by gene knockout. The knockout mutant ΔCsste50 had pleiotropic phenotypes in development and pathogenicity. Compared with the wild-type, the mutants grew faster and produced more conidia on regular agar but were more sensitive to osmotic stress. On artificial and plant surfaces, the conidia of the mutant showed significantly reduced germination and failed to form appressoria. The mutant was completely non-pathogenic on pepper fruits with or without wounds, indicating that pre-penetration and invasive growth were both defective in the mutant. Our results show that the adaptor protein CsSTE50 plays a role in vegetative growth, conidiation, germination, appressorium formation, and pathogenicity in C. scovillei.

NADPH Oxidases Are Required for Appressorium-Mediated Penetration in Colletotrichum scovillei-Pepper Fruit Pathosystem

NADPH oxidase (Nox) complexes are known to play essential roles in differentiation and proliferation of many filamentous fungi. However, the functions of Noxs have not been elucidated in Colletotrichum species. Therefore, we set out to characterize the roles of Nox enzymes and their regulators in Colletotrichum scovillei, which causes serious anthracnose disease on pepper fruits in temperate and subtropical and temperate region. In this study, we generated targeted deletion mutants for CsNox1, CsNox2, CsNoxR, and CsNoxD via homologous recombination. All deletion mutants were normal in mycelial growth, conidiation, conidial germination, and appressorium formation, suggesting that CsNox1, CsNox2, CsNoxR, and CsNoxD are not involved in those developmental processes. Notably, conidia of ΔCsnox2 and ΔCsnoxr, other than ΔCsnox1 and ΔCsnoxd, failed to cause anthracnose on intact pepper fruits. However, they still caused normal disease on wounded pepper fruits, suggesting that Csnox2 and CsnoxR are essential for penetration-related morphogenesis in C. scovillei. Further observation proved that ΔCsnox2 and ΔCsnoxr were unable to form penetration peg, while they fully developed appressoria, revealing that defect of anthracnose development by ΔCsnox2 and ΔCsnoxr resulted from failure in penetration peg formation. Our results suggest that CsNox2 and CsNoxR are critical for appressorium- mediated penetration in C. scovillei-pepper fruit pathosystem, which provides insight into understanding roles of Nox genes in anthracnose disease development.

First report of Colletotrichum scovillei causing anthracnose fruit rot on Eriobotrya japonicain in Zhejiang province, China

Loquat (Eriobotrya japonica (Thunb.) Lindl.) is a fruit tree of high economic impotance in China. In May 2021, fruit rot on cv. "Baozhu" was observed in Yuhang district (119°40'E, 30°09'N), Zhejiang province, at an incidence of more than 30% within five orchards (the total affected area were about 121, 000 m2). Early symptoms of naturally affected fruits were dark brown, necrotic lesion (Fig. 1 A). Lesions subsequently expanded, and orange conidia were observed (Fig. 1 B). Conidia were transferred using a sterilized needle into sterile water, diluted to several conidia (approximately 10 conidia/µL) in the field of light microscope, and spread onto potato dextrose agar (PDA). After 24 h, single colonies were transferred, and six single-spore strain isolated from different fruits or locations were obtained. Six-day old colonies grown on PDA at 27°C had gray-green centers with white edges, and on the reverse side, the centers were brown (Fig. 1 C). Isolate PPGS2 was selected for further characterization. Conidia were unicellular, smooth-walled, hyaline, cylindrical with one rounded and one acute end, or with both ends rounded and they (n = 30) measured 11.1 to 16.0 µm (mean = 13.3 µm) × 3.0 to 4.6 µm (mean = 4.1) (Fig. 1 D). Appressoria were single or in smalln groups, light brown to dark brown, ovoid or elliptical with a smooth or undulate outline, and measured (n = 30) 4.6 to 8.7 µm (mean = 6.5 µm) × 4.0 to 5.6 µm (mean = 4.9 µm) (Fig. 1 H). These features of PPGS2 were consistent with species of the Colletotrichum acutatum species complex (Damm et al. 2012). For species identification, the internal transcribed spacer (ITS), beta-tubulin (TUB), chitin synthase (CHS-1), calmodulin (CAL), and actin (ACT) genes were sequenced (O'Donnell et al. 2000; Weir et al. 2012). The five sequences were deposited in GenBank (OK054581, OK077960, OK077987, OK077988 and OK077989, respectively). A BLAST search of these sequences showed 99% identity with sequences of the ex-holotype C. scovillei CBS126529 (Damm et al. 2012). The evolutionary tree shown that PPGS2 and C. scovillei CBS126529 were clustered in a branch (SH-aLRT/approximate Bayes test/bootstrap support = 88.6/0.999/96). Combining morphological characteristics with phylogenetic analysis, PPGS2 was identified as C. scovillei. To fulfill Koch's postulates, E. japonica fruit were disinfected with 75% alcohol and air-dried for 5 mins to allow the alcohol to volatilize. A conidial suspension (10 mL of 1 × 106 conidia/ml) of PPGS2 was sprayed onto six fruits, and six fruit sprayed with sterilized water served as controls. The experiment was repeated three times. Fruits were kept on a mist bench at 27°C and 80% relative humidity for 5 days. Inoculated fruit developed dark brown necrotic lesions that later fused and expanded (Fig. 1, E-G), whereas control fruit remained symptomless. C. scovillei was re-isolated from lesions of inoculated fruit. C. scovillei has been reported from fruit of Capsicum sp., Musa sp., Mangifera indica, and Clausena lansium in China (Farr and Rossman 2021). To our knowledge, this is the first report of C. scovillei causing anthracnose fruit rot of E. japonica in China. This disease results in severe economic losses both in the field and after harvest, and it is necessary to develop more effective prevention and control strategies.

Mitogen-Activated Protein Kinase CsPMK1 Is Essential for Pepper Fruit Anthracnose by Colletotrichum scovillei

The phytopathogenic fungus Colletotrichum scovillei, belonging to the Colletotrichum acutatum species complex, causes severe anthracnose disease on several fruits, including chili pepper (Capsicum annuum). However, the molecular mechanisms underlying the development and pathogenicity of Colletotrichum scovillei are unclear. The conserved Fus3/Kss1-related MAPK regulates fungal development and pathogenicity. Here, the role of CsPMK1, orthologous to Fus3/Kss1, was characterized by phenotypic comparison of a target deletion mutant (ΔCspmk1). The mycelial growth and conidiation of ΔCspmk1 were normal compared to that of the wild type. ΔCspmk1 produced morphologically abnormal conidia, which were delayed in conidial germination. Germinated conidia of ΔCspmk1 failed to develop appressoria on inductive surfaces of hydrophobic coverslips and host plants. ΔCspmk1 was completely defective in infectious growth, which may result from failure to suppress host immunity. Furthermore, ΔCspmk1 was impaired in nuclear division and lipid mobilization during appressorium formation, in response to a hydrophobic surface. CsPMK1 was found to interact with CsHOX7, a homeobox transcription factor essential for appressorium formation, via a yeast two-hybridization analysis. Taken together, these findings suggest that CsPMK1 is required for fungal development, stress adaptation, and pathogenicity of C. scovillei.

The Small GTPase CsRAC1 Is Important for Fungal Development and Pepper Anthracnose in Colletotrichum scovillei

The pepper anthracnose fungus, Colletotrichum scovillei, causes severe losses of pepper fruit production in the tropical and temperate zones. RAC1 is a highly conserved small GTP-binding protein in the Rho GTPase family. This protein has been demonstrated to play a role in fungal development, and pathogenicity in several plant pathogenic fungi. However, the functional roles of RAC1 are not characterized in C. scovillei causing anthracnose on pepper fruits. Here, we generated a deletion mutant (ΔCsrac1) via homologous recombination to investigate the functional roles of CsRAC1. The ΔCsrac1 showed pleiotropic defects in fungal growth and developments, including vegetative growth, conidiogenesis, conidial germination and appressorium formation, compared to wild-type. Although ΔCsrac1 was able to develop appressoria, it failed to differentiate appressorium pegs. However, ΔCsrac1 still caused anthracnose disease with significantly reduced rate on wounded pepper fruits. Further analyses revealed that ΔCsrac1 was defective in tolerance to oxidative stress and suppression of host-defense genes. Taken together, our results suggest that CsRAC1 plays essential roles in fungal development and pathogenicity in C. scovillei-pepper fruit pathosystem.

Pex7 selectively imports PTS2 target proteins to peroxisomes and is required for anthracnose disease development in Colletotrichum scovillei

Pex7 is a shuttling receptor that imports matrix proteins with a type 2 peroxisomal targeting signal (PTS2) to peroxisomes. The Pex7-mediated PTS2 protein import contributes to crucial metabolic processes such as the fatty acid β-oxidation and glucose metabolism in a number of fungi, but cellular roles of Pex7 between the import of PTS2 target proteins and metabolic processes have not been fully understood. In this study, we investigated the functional roles of CsPex7, a homolog of the yeast Pex7, by targeted gene deletion in the pepper anthracnose fungus Colletotrichum scovillei. CsPex7 was required for carbon source utilization, scavenging of reactive oxygen species, conidial production, and disease development in C. scovillei. The expression of fluorescently tagged PTS2 signal of hexokinases and 3-ketoacyl-CoA thiolases showed that peroxisomal localization of the hexokinase CsGlk1 PTS2 is dependent on CsPex7, but those of the 3-ketoacyl-CoA thiolases are independent on CsPex7. In addition, GFP-tagged CsPex7 proteins were intensely localized to the peroxisomes on glucose-containing media, indicating a role of CsPex7 in glucose utilization. Collectively, these findings indicate that CsPex7 selectively recognizes specific PTS2 signal for import of PTS2-containing proteins to peroxisomes, thereby mediating peroxisomal targeting efficiency of PTS2-containing proteins in C. scovillei. On pepper fruits, the ΔCspex7 mutant exhibited significantly reduced virulence, in which excessive accumulation of hydrogen peroxide was observed in the pepper cells. We think the reduced virulence results from the abnormality in hydrogen peroxide metabolism of the ΔCspex7 mutant. Our findings provide insight into the cellular roles of CsPex7 in PTS2 protein import system.

Homeobox Transcription Factors Are Required for Fungal Development and the Suppression of Host Defense Mechanisms in the Colletotrichum scovillei-Pepper Pathosystem

Colletotrichum scovillei, an ascomycete phytopathogenic fungus, is the main causal agent of serious yield losses of economic crops worldwide. The fungus causes anthracnose disease on several fruits, including peppers. However, little is known regarding the underlying molecular mechanisms involved in the development of anthracnose caused by this fungus. In an initial step toward understanding the development of anthracnose on pepper fruits, we retrieved 624 transcription factors (TFs) from the whole genome of C. scovillei and comparatively analyzed the entire repertoire of TFs among phytopathogenic fungi. Evolution and proliferation of members of the homeobox-like superfamily, including homeobox (HOX) TFs that regulate the development of eukaryotic organisms, were demonstrated in the genus Colletotrichum. C. scovillei was found to contain 10 HOX TF genes (CsHOX1 to CsHOX10), which were functionally characterized using deletion mutants of each CsHOX gene. Notably, CsHOX1 was identified as a pathogenicity factor required for the suppression of host defense mechanisms, which represents a new role for HOX TFs in pathogenic fungi. CsHOX2 and CsHOX7 were found to play essential roles in conidiation and appressorium development, respectively, in a stage-specific manner in C. scovillei. Our study provides a molecular basis for understanding the mechanisms associated with the development of anthracnose on fruits caused by C. scovillei, which will aid in the development of novel approaches for disease management. IMPORTANCE The ascomycete phytopathogenic fungus, Colletotrichum scovillei, causes serious yield loss on peppers. However, little is known about molecular mechanisms involved in the development of anthracnose caused by this fungus. We analyzed whole-genome sequences of C. scovillei and isolated 624 putative TFs, revealing the existence of 10 homeobox (HOX) transcription factor (TF) genes. We found that CsHOX1 is a pathogenicity factor required for the suppression of host defense mechanism, which represents a new role for HOX TFs in pathogenic fungi. We also found that CsHOX2 and CsHOX7 play essential roles in conidiation and appressorium development, respectively, in a stage-specific manner in C. scovillei. Our study contributes to understanding the mechanisms associated with the development of anthracnose on fruits caused by C. scovillei, which will aid for initiating novel approaches for disease management.

Antagonistic and Plant Growth-Promoting Effects of Bacillus velezensis BS1 Isolated from Rhizosphere Soil in a Pepper Field

Pepper (Capsicum annuum L.) is an important agricultural crop worldwide. Recently, Colletotrichum scovillei, a member of the C. acutatum species complex, was reported to be the dominant pathogen causing pepper anthracnose disease in South Korea. In the present study, we isolated bacterial strains from rhizosphere soil in a pepper field in Gangwon Province, Korea, and assessed their antifungal ability against C. scovillei strain KC05. Among these strains, a strain named BS1 significantly inhibited mycelial growth, appressorium formation, and disease development of C. scovillei. By combined sequence analysis using 16S rRNA and partial gyrA sequences, strain BS1 was identified as Bacillus velezensis, a member of the B. subtilis species complex. BS1 produced hydrolytic enzymes (cellulase and protease) and iron-chelating siderophores. It also promoted chili pepper (cv. Nockwang) seedling growth compared with untreated plants. The study concluded that B. velezensis BS1 has good potential as a biocontrol agent of anthracnose disease in chili pepper caused by C. scovillei.

Genome Sequence Resource for Colletotrichum scovillei, the Cause of Anthracnose Disease of Chili

Colletotrichum species cause anthracnose disease on the economically important spice crop chili. A total of 24 Colletotrichum species are known to infect chili and cause anthracnose. C. scovillei belongs to the C. acutatum species complex, and it shows greater aggressiveness than other species, particularly in the case of inoculation onto the nonwounded fruits of chili plants. The current work introduces an initial Illumina-Nanopore hybrid draft genome for C. scovillei TJNH1 together with the related annotations. Knowledge of this genome sequence provides an important reference genome of C. scovillei and will help further understand the pathogenic mechanism of C. scovillei to plant.[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.

First Report of Colletotrichum scovillei Causing Anthracnose Fruit Rot on Pepper in South Carolina, United States

Anthracnose fruit rot caused by various Colletotrichum spp. is a serious disease for pepper (Capsicum annuum) growers, resulting in extensive fruit loss (Harp et al. 2008). Samples of five pepper fruits were obtained from two commercial farms in Lexington and Pickens counties, South Carolina, in August and September 2019, respectively. All fruits had two or more soft, sunken lesions covered with salmon-colored spore masses. Pieces of diseased tissue cut from the margins of lesions were surface disinfested in 0.6% sodium hypochlorite, rinsed in sterile deionized water, blotted dry, and placed on one-quarter-strength potato dextrose agar (PDA/4) amended with 100 mg chloramphenicol, 100 mg streptomycin sulfate, and 60.5 mg mefenoxam (0.25 ml Ridomil Gold EC) per liter. Two isolates of Colletotrichum sp. per fruit were preserved on dried filter paper and stored at 10º C. One additional isolate of Colletotrichum sp. had been collected from a jalapeño pepper fruit on a farm in Charleston County, South Carolina, in 1997. Colony morphology of three isolates, one per county, on Spezieller Nährstoffarmer Agar (SNA) was pale grey with a faint orange tint. All isolates readily produced conidia on SNA with an average length of 16.4 μm (std. dev. = 1.8 μm) and a width of 2.2 μm (std. dev. = 0.2 μm). Conidia were hyaline, smooth, straight, aseptate, cylindrical to fusiform with one or both ends slightly acute or round, matching the description of C. scovillei (Damm et al. 2012). The glyceraldehyde-3-phosphate dehydrogenase (GAPDH) and beta-tubulin (TUB2) genes from three isolates were amplified and sequenced with the primer pairs GDF1/GDR1 and T1/Bt2b, respectively. Species within the C. acutatum clade can be readily distinguished with GAPDH or TUB2 (Cannon et al. 2012). The GAPDH and TUB2 sequences for all three isolates were 100% similar to each other and strain CBS 126529 (GAPDH accession number JQ948597; TUB2 accession number JQ949918) of C. scovillei (Damm et al. 2012). GAPDH and TUB2 sequences for each isolate were deposited in GenBank under the accessions MT826948-MT826950 and MT826951-MT826953, respectively. A pathogenicity test was conducted on jalapeño pepper fruits by placing a 10-ul droplet of a 5 x 105 conidial suspension of each isolate onto a wound made with a sterile toothpick. Control peppers were mock inoculated with 10 ul sterile distilled water. A humid chamber was prepared by placing moist paper towels on the bottom of a sealed crisper box. Inoculated peppers were placed on upside-down 60 ml plastic condiment cups. Three replicate boxes each containing all four treatments were prepared. The experiment was repeated once. After 7 days in the humid chamber at 26ºC, disease did not develop on control fruits, whereas soft, sunken lesions covered with salmon-colored spores developed on inoculated fruits. Lesions were measured and C. scovillei was re-isolated onto amended PDA/4 as previously described. Lesion length averaged 15.6 mm (std dev. = 4.1 mm) by 11.5 mm (std dev. = 2.0 mm). Colletotrichum sp. resembling the original isolate were recovered from all inoculated fruit, but not from non-inoculated fruit. C. scovillei has been reported in Brazil in South America and in China, Indonesia, Japan, Malaysia, South Korea, Taiwan, and Thailand in Asia (Farr and Rossman 2020). This is the first report of C. scovillei as the casual organism of anthracnose fruit rot on pepper in South Carolina and the United States.

Fine mapping of the major anthracnose resistance QTL AnRGO5 in Capsicum chinense 'PBC932'

BACKGROUND

Colletotrichum species are the causal agents of anthracnose, a major disease affecting the yield and quality of pepper (Capsicum spp.). Colletotrichum scovillei is widespread in China, has strong pathogenicity and drug resistance, and causes anthracnose disease in pepper fruits that severely reduces production. Previously, an anti-anthracnose locus AnR_GO5 was mapped to the P5 chromosome on the basis of analyses of fruit at the green mature stage. The aim of this study was to narrow down the interval of this locus and identify the gene responsible for conferring resistance.

RESULTS

On the basis of results of re-sequencing of Capsicum chinense 'PBC932' and C. annuum '77013', we developed Kompetitive allele-specific PCR (KASPar) markers and insertion-deletion (InDel) markers linked to AnR_GO5 at the green mature fruit stage and used them to construct a genetic linkage map (42 markers, 24.4 cM in length). Using data obtained in phenotypic and genotypic analyses of BC₄S₁, BC₄S₂, and BC₄S₃ populations, AnR_GO5 was located between the markers P5in-2266-404 and P5in-2268-978 within a physical distance of 164 kb. This region contained five genes, including CA05g17730. CA05g17730 encodes 'R1C-3-like' putative late blight resistance protein homologs. The transcript level of CA05g17730 differed between 'PBC932' and '77013'. The structure of the CA05g17730 gene also differed between 'PBC932' and '77013'.

CONCLUSIONS

We narrowed down the QTL interval to a region containing five genes. These results will be useful for further research on the mechanisms of resistance to anthracnose, and for marker assisted selection for anthracnose-resistant capsicum lines.

Effect of Pyrisoxazole on Colletotrichum scovillei Infection and Anthracnose on Chili

Anthracnose caused by Colletotrichum scovillei is one of the most destructive diseases affecting chili production. Disease control mainly relies on conventional fungicides, and repeated exposure to single-site mode-of-action fungicides may pose a risk for the development of resistant isolates within the population. Our previous study suggested that pyrisoxazole has strong inhibitory activity against C. scovillei in vitro. However, the effects of pyrisoxazole on the C. scovillei infection process and the performance of pyrisoxazole in the field remain unclear. In this study, pyrisoxazole exhibited strong inhibitory activity against the mycelial growth, appressorium formation, and appressorium diameter of C. scovillei, with half maximal effective concentration values of 0.1986, 0.0147, and 0.0269 μg/ml, respectively, but had no effect on sporulation, even at the highest concentration of 1.6 μg/ml. The baseline sensitivity curves were unimodal with a long right-hand tail. The in vivo data showed that pyrisoxazole provided both preventive and curative activity against anthracnose on chili. Pyrisoxazole decreased the incidence of anthracnose and reduced disease progress. The results of electron microscopy showed that pyrisoxazole can affect the C. scovillei infection process by altering mycelial morphology, degrading conidia and germ tubes, suppressing conidial germination and appressorium formation, and enhancing conidiophore production. Pyrisoxazole can be used to effectively control anthracnose under field conditions and increase chili yield; moreover, no phytotoxicity symptoms were observed after treatment. These results provide new insight into the mechanisms by which pyrisoxazole controls disease and suggest that pyrisoxazole is a feasible alternative for the management of anthracnose in chili.

Optimization of Polyethylene Glycol-Mediated Transformation of the Pepper Anthracnose Pathogen Colletotrichum scovillei to Develop an Applied Genomics Approach

Colletotrichum acutatum is a species complex responsible for anthracnose disease in a wide range of host plants. Strain C. acutatum KC05, which was previously isolated from an infected pepper in Gangwon Province of South Korea, was reidentified as C. scovillei using combined sequence analyses of multiple genes. As a prerequisite for understanding the pathogenic development of the pepper anthracnose pathogen, we optimized the transformation system of C. scovillei KC05. Protoplast generation from young hyphae of KC05 was optimal in an enzymatic digestion using a combined treatment of 2% lysing enzyme and 0.8% driselase in 1 M NH₄Cl for 3 h incubation. Prolonged incubation for more than 3 h decreased protoplast yields. Protoplast growth of KC05 was completely inhibited for 4 days on regeneration media containing 200 μg/ml hygromycin B, indicating the viability of this antibiotic as a selection marker. To evaluate transformation efficiency, we tested polyethylene glycol-mediated protoplast transformation of KC05 using 19 different loci found throughout 10 (of 27) scaffolds, covering approximately 84.1% of the entire genome. PCR screening showed that the average transformation efficiency was about 17.1% per 100 colonies. Southern blot analyses revealed that at least one transformant per locus had single copy integration of PCR-screened positive transformants. Our results provide valuable information for a functional genomics approach to the pepper anthracnose pathogen C. scovillei.

Toxicity and biochemical action of the antibiotic fungicide tetramycin on Colletotrichum scovillei

Tetramycin, a novel polyene macrolide antibiotic, has strong activity against a broad spectrum of fungi and may have potential uses in future agricultural applications. Thus, the antifungal activity and biochemical action of tetramycin on Colletotrichum scovillei were investigated in this study. The experimental results indicated that tetramycin had strong inhibitory activity against the mycelial growth, spore germination and germ tube elongation of C. scovillei. The baseline sensitivity curves were unimodal, with mean EC₅₀ values of 1.98 ± 0.078 μg/mL and 0.003 ± 0.005 μg/mL for mycelial growth and spore germination inhibition, respectively. Tetramycin also inhibited the germination of spores and formation of appressoria. After tetramycin treatment, the edge of the mycelial diaphragm showed protuberances, with decreased offshoots at the top. Additionally, disruption of the membrane was detected through an increase in membrane permeability, leakage of sugars and a reduction in the ergosterol content. Tetramycin effectively controlled C. scovillei on detached pepper fruits. These results will contribute to our evaluation of the potential of tetramycin for successful management of pepper anthracnose and to our understanding of the possible biochemical action of tetramycin against C. scovillei.

Characterization and Pathogenicity of New Record of Anthracnose on Various Chili Varieties Caused by Colletotrichum scovillei in Korea

The anthracnose disease caused by Colletotrichum species is well-known as a major plant pathogen that primarily causes fruit rot in pepper and reduces its marketability. Thirty-five isolates representing species of Colletotrichum were obtained from chili fruits showing anthracnose disease symptoms in Chungcheongnam-do and Chungcheongbuk-do, South Korea. These 35 isolates were characterized according to morphological characteristics and nucleotide sequence data of internal transcribed spacer, glyceraldehyde-3-phosphate-dehydrogenase, and β-tubulin. The combined dataset shows that all of these 35 isolates were identified as C. scovillei and morphological characteristics were directly correlated with the nucleotide sequence data. Notably, these isolates were recorded for the first time as the causes of anthracnose caused by C. scovillei on pepper in Korea. Forty cultivars were used to investigate the pathogenicity and to identify the possible source of resistance. The result reveals that all of chili cultivars used in this study are susceptible to C. scovillei.