Characterization, Phylogenetic Analyses, and Pathogenicity of Colletotrichum Species on Morus alba in Sichuan Province, China

A Biological Comparison of Three Colletotrichum Species Associated with Alfalfa Anthracnose in Northern China

Anthracnose caused by various species of Colletotrichum is one of the most prevalent diseases in alfalfa worldwide that not only reduces forage yields but also severely compromises forage quality. A comprehensive survey was conducted in 2020 in the main production regions of northern China. The survey results showed that alfalfa anthracnose is prevalent in northern China, with the disease incidence ranging from 9% to 45% and the disease index from 5 to 17 (maximum possible score: 100). In total, 24 isolates were collected and identified as three Colletotrichum species (C. trifolii, C. truncatum and C. americae-borealis) based on morphological characteristics and phylogenetic analysis (combined sequences ITS, HIS3, ACT and GAPDH). The three species displayed remarkable environmental adaptability, exhibiting a capacity for growth, sporulation and conidial germination in temperatures ranging from 4 to 35 °C and in different nutrient conditions. Pathogenicity assays showed that C. trifolii was more virulent than the other two species, although the growth vigor (in terms of colony diameter, sporulation and conidial germination) of C. truncatum was the greatest.

Identification and Fungicide Screening of Fungal Species Associated with Walnut Anthracnose in Shaanxi and Liaoning Provinces, China

Walnut is cultivated around the world for its precious woody nut and edible oil. Recently, walnut infected by Colletotrichum spp. resulted in a great yield and quality loss. In August and September 2014, walnut fruits with anthracnose were sampled from two commercial orchards in Shaanxi and Liaoning provinces, and five representative isolates were used in this study. To identify the pathogen properly, four genes per region (internal transcribed spacer, glyceraldehyde-3-phosphate dehydrogenase, actin, and chitin synthase) were sequenced and used in phylogenetic studies. Based on multilocus phylogenetic analysis, five isolates clustered with Colletotrichum fioriniae, including its ex-type, with 100% bootstrap support. The results of multilocus phylogenetic analyses, morphology, and pathogenicity confirmed that C. fioriniae was one of the walnut anthracnose pathogens in China. All 13 fungicides tested inhibited mycelial growth and spore germination. Flusilazole, fluazinam, prochloraz, and pyraclostrobin showed the strongest suppressive effects on the mycelial growth than the others, the average EC50 values ranged from 0.09 to 0.40 μg/ml, and there was not any significant difference (P < 0.05). Pyraclostrobin, thiram, and azoxystrobin were the most effective fungicides on spore germination (P < 0.05), and the EC50 values ranged from 0.01 to 0.44 μg/ml. Pyraclostrobin, azoxystrobin, fluazinam, flusilazole, mancozeb, thiram, and prochloraz exhibited a good control effect on walnut anthracnose caused by C. fioriniae, and preventive activities were greater than curative activities. Pyraclostrobin at 250 a.i. μg/ml and fluazinam at 500 a.i. μg/ml provided the highest preventive and curative efficacy, and the values ranged from 81.3 to 82.2% and from 72.9 to 73.6%, respectively. As a consequence, mancozeb and thiram could be used at the preinfection stage, and pyraclostrobin, azoxystrobin, flusilazole, fluazinam, and prochloraz could be used at the early stage for effective prevention and control of walnut anthracnose caused by C. fioriniae. The results will provide more significant instructions for controlling the disease effectively in northern China.

First Report of Colletotrichum fructicola, C. rhizophorae sp. nov. and C. thailandica sp. nov. on Mangrove in Thailand

Colletotrichum, a genus within the phylum Ascomycota (Fungi) and family Glomerellaceae are important plant pathogens globally. In this paper, we detail four Colletotrichum species found in mangrove ecosystems. Two new species, Colletotrichum rhizophorae and C. thailandica, and a new host record for Colletotrichum fructicola were identified in Thailand. Colletotrichum tropicale was collected from Taiwan's mangroves and is a new record for Rhizophora mucronata. These identifications were established through a combination of molecular analysis and morphological characteristics. This expanded dataset for Colletotrichum enhances our understanding of the genetic diversity within this genus and its associations with mangrove ecosystems. The findings outlined herein provide data on our exploration of mangrove pathogens in Asia.

First Report on Choanephora cucurbitarum Causing Choanephora Rot in Chenopodium Plants and Its Sensitivity to Fungicide

Choanephora rot of Chenopodium plants (CRC) was observed at the flowering stages in seven plantations of Shanxi Province, China. CRC had caused leaf, stem, and panicle neck rot of C. quinoa, panicle neck and stem rot of C. formosanum, and stem rot of C. album. Typical symptoms included water-soaked, rapid soft rotting, and abundant sporulation on the whole panicle necks, stems, and leaves. Based on morphological characteristics, phylogenetic analyses, and pathogenicity tests, the pathogens were identified as Choanephoraceae cucurbitarum. Sporangiola and sporangiospore of C. cucurbitarum germinated at 30 °C and were able to germinate by two h post-inoculation (hpi). The germination rates of sporangiola and sporangiospore significantly increased at 3 to 4 hpi, and the germination rates ranged from 91.53 to 97.67%. The temperature had a significant effect on the pathogenicity of C. cucurbitarum the optimum pathogenic temperatures for stems of C. quinoa, C. formosanum and C. album were 30 °C after one day post-inoculation. Choanephoraceae cucurbitarum could infect white and red quinoa panicle necks between 20 and 30 °C, and the average lesion lengths were 0.21 to 3.62 cm. Among the five tested fungicides (boscalid, dimethomorph, isopyrazam, propiconazole, and tebuconazole), isopyrazam showed higher sensitivity to sporangiola germination of C. cucurbitarum, with an EC50 value of 0.6550 μg/mL. Isopyrazam and tebuconazole strongly inhibited the sporangiospore germination of C. cucurbitarum, which showed EC50 values of 0.4406 and 0.3857 μg/mL. To our knowledge, the present study found for the first time that C. cucurbitarum is a pathogen causing panicle neck of C. formosanum and stem rot of C. formosanum and C. album, while CRC first appeared in the quinoa panicle necks, and gradually expanded to stems and leaves.

Species of the Colletotrichum spp., the Causal Agents of Leaf Spot on European Hornbeam (Carpinus betulus)

European hornbeam (Carpinus betulus L.) is widely planted in landscaping. In October 2021 and August 2022, leaf spot was observed on C. betulus in Xuzhou, Jiangsu Province, China. To identify the causal agent of anthracnose disease on C. betulus, 23 isolates were obtained from the symptomatic leaves. Based on ITS sequences and colony morphology, these isolates were divided into four Colletotrichum groups. Koch's postulates of four Colletotrichum species showed similar symptoms observed in the field. Combining the morphological characteristics and multi-gene phylogenetic analysis of the concatenated sequences of the internal transcribed spacer (ITS) gene, Apn2-Mat1-2 intergenic spacer (ApMat) gene, the calmodulin (CAL) gene, glyceraldehyde3-phosphate dehydrogenase (GAPDH) gene, Glutamine synthetase (GS) gene, and beta-tubulin 2 (TUB2) genes, the four Colletotrichum groups were identified as C. gloeosporioides, C. fructicola, C. aenigma, and C. siamense. This study is the first report of four Colletotrichum species causing leaf spot on European hornbeam in China, and it provides clear pathogen information for the further evaluation of the disease control strategies.

Morphological, Pathological and Genetic Diversity of the Colletotrichum Species, Pathogenic on Solanaceous Vegetable Crops in Bulgaria

Colletotrichum species are among the most devastating plant pathogens in a wide range of hosts. Their accurate identification requires a polyphasic approach, including geographical, ecological, morphological, and genetic data. Solanaceous crops are of significant economic importance for Bulgarian agriculture. Colletotrichum-associated diseases pose a serious threat to the yield and quality of production but are still largely unexplored. The aim of this study was to identify and characterize 26 pathogenic Colletotrichum isolates that threaten solanaceous crops based on morphological, pathogenic, and molecular data. DNA barcodes enabled the discrimination of three main taxonomic groups: C. acutatum, C. gloeosporioides, and C. coccodes. Three different species of acutatum complex (C. nymphaeae, C. godetiae, and C. salicis) and C. cigarro of the gloeosporioides complex were associated with fruit anthracnose in peppers and tomatoes. The C. coccodes group was divided in two clades: C. nigrum, isolated predominantly from fruits, and C. coccodes, isolated mainly from roots. Only C. salicis and C. cigarro produced sexual morphs. The species C. godetiae, C. salicis, and C. cigarro have not previously been reported in Bulgaria. Our results enrich the knowledge of the biodiversity and specific features of Colletotrichum species, which are pathogenic to solanaceous hosts, and may serve as a scientific platform for efficient disease control and resistance breeding.

First Report of Colletotrichum aenigma Causing Anthracnose on Mulberry Leaves in China

Mulberry (Morus alba L.) has been grown worldwide as a crop for silkworm rearing for over five thousand years (Jiao et al. 2020). In July 2021, a leaf spot disease was observed on mulberry leaves in Wuhan city (114°33'E, 30°48'N), Hubei province, China, with approximately 40% of leaves (about 300 trees) affected. Early symptoms were light brown, with small lesions subsequently expanding to larger sometimes irregular dark brown or black spots surrounded by yellow-brown margins, with easily perforated necrotic lesions. Leaf tissues (5 mm×5 mm) were excised from the border between diseased and healthy tissues, surface sterilized with 75% ethanol solution for 30 s and 2.5% sodium hypochlorite for 2 min, washed thrice in sterile distilled water, and then placed on potato dextrose agar (PDA), and incubated at 25°C in darkness. Four isolates (C1, C9, CHS2, and CHS6) were subcultured using the single-spore method. On PDA, colonies were cottony, pale white from above, and white to grayish-green on the reverse side. Conidia were aseptate, hyaline, subcylindrical with broadly rounded ends, 8.4 to 18.3×4.1 to 7.7 μm (mean = 13.9×5.5 μm, n = 30). Appressoria were typically elliptic or irregular with a few lobes, dark brown, 5.9 to 9.6×4.2 to 8.1 μm (mean = 7.9 ×5.7 μm, n = 30). The morphological characteristics of the isolates matched the descriptions of Colletotrichum gloeosporioides species complex (Weir et al. 2012). The isolates were further identified by analysis of the ribosomal internal transcribed spacers (ITS), glyceraldehyde-3-phosphate dehydrogenase (GAPDH), calmodulin (CAL), actin (ACT), chitin synthase (CHS-1), glutamine synthetase (GS), and β-tubulin 2 (TUB2) genes, amplified respectively with ITS1/ITS4, GDF/GDR, CL1C/CL2C, ACT-512F/ACT-783R, CHS-79F/CHS-345R, GSF1/GSR, and Bt2a/Bt2b (Glass and Donaldson 1995; Weir et al. 2012; White et al. 1990). The sequences were deposited in GenBank (ON492187-ON492214). Concatenated sequences of the seven genes in addition to Colletotrichum species sequences from GenBank were used to conduct a phylogenetic analysis using Maximum-Likelihood (ML) method in MEGA7. The four isolates were grouped into a clade with Colletotrichum aenigma supported by a high bootstrap value (89%), and hence, they were identified as C. aenigma based on the morphological and molecular analyses. To confirm Koch's postulates, wounded leaves of six healthy 2-month-old seedlings made by a sterile needle were inoculated with each isolate by spraying 10 ml of conidial suspensions (105 conidia/ml) on each plant, and the control plants were treated with sterile distilled water. All the treated plants were kept in a plastic box containing sterile water and incubated at 28°C in a 12 h/12 h light/dark cycle. The test was performed three times. After 7 days, typical anthracnose lesions appeared on all inoculated leaves, whereas control plants remained asymptotic. Furthermore, C. aenigma was only reisolated from the symptomatic leaves. Previous studies reported five Colletotrichum species (C. morifolium, C. fioriniae, C. brevisporum, C. karstii, and C. kahawae subsp. ciggaro) to cause this disease on mulberry in China (Tian, 1981; Xue et al. 2019). To our knowledge, this is the first report of C. aenigma causing anthracnose on mulberry in China. The finding will facilitate epidemiological studies and the development of effective control strategies for the disease.

First report of Colletotrichum fioriniae causing leaf spot on Schima superba in the world

Schima superba Gardn. et Champ. is a subtropical evergreen tree species naturally distributed mainly in China, Japan, and Vietnam. It is primarily planted for its timber and urban landscaping in China (Ni, 1996). In September 2018, leaves necrotic spots were observed on S. superba in Jiangxi Forest Breeding Center (28°57'19.52" N, 115°39'21.32" E), Jiangxi Province, China. The disease incidence was about 30%. Initially, spots were circular to semicircular, grayish-brown in the center with dark brown margin, then expanded and eventually collapsed into sunken necrotic lesions. To identify the agent, diseased leaves were collected randomly. Pieces (5 × 5 mm) from the lesion borders were surfaced sterilized in 70% ethanol (30 s), 3% NaOCl (60 s), and rinsed 3 times in sterile water. These pieces were put on potato dextrose agar (PDA) and cultured at 25 °C. Pure cultures were obtained by monosporic isolation, and 3 isolates (MH-1, MH-2, MH-3) were used for morphological studies and phylogenetic analyses. On PDA, colonies were initially white, cottony, then became pinkish to deep-pink at the center and pink on the reverse. Conidia were fusiform with acute ends, smooth-walled, hyaline, 13.7-18.5 × 4.6-6.1 µm (16.4 ± 1.3× 5.3 ± 0.6 µm, n = 100). Conidiophores were colorless to pale brown, smooth, septate. Conidiogenous cells were colorless to pale brown, smooth, cylindrical to ampulliform. The morphological characteristics fit the descriptions of Colletotrichum acutatum J. H. Simmonds sensu lato (Damm et al., 2012). For accurate identification, genomic DNA of 3 isolates was extracted, and the internal transcribed spacer (ITS), actin (ACT), glyceraldehyde-3-phosphate dehydrogenase (GAPDH), beta-tubulin 2 (TUB2), and chitin synthase (CHS-1) were amplified and sequenced using the corresponding primers (Weir et al., 2012). The sequences were deposited in GenBank (ITS: MZ325946, MZ325947, MW584318; ACT: MZ399375, MZ419566, MW661171; CHS-1: MZ399376, MZ419567, MW661172; MZ399377, GAPDH: MZ419568, MW661173; TUB2: MZ399378, MZ419569, MW661174). Five loci were concatenated, and the aligned sequences (1528bp) were 99.89% homologous to ex-type C. fioriniae (Marcelino & Gouli) R. G. Shivas & Y. P. Tan CBS128517. Phylogenetic analysis using the maximum likelihood showed that 3 isolates were clustered in C. fioriniae clade with 100% bootstrap support. Based on the multi-locus phylogeny and morphology, 3 isolates were identified as C. fioriniae. Pathogenicity tests were performed on 36 seedlings of S. superba (2-year-old). The leaves were wounded slightly and inoculated with a drop of spore suspension (106 conidia/mL). The sterile water was used as controls. All the tested leaves were covered with black plastic bags to keep them moist for 2 days. All seedlings were placed in the greenhouse (25 °C, 12 h light/dark) for 10 days, and all inoculated leaves had typical symptoms. The controls were asymptomatic. The same fungus was reisolated from the lesions, fulfilling Koch's postulates. Colletotrichum fioriniae was described as a new species from the C. acutatum s. l. (Shivas et al., 2009), and it was an important plant pathogen, such as Pyrus spp. (Pavlović et al., 2019), Morus alba L. (Xue et al., 2019), and so on. This is the first report of the newly emerging disease of S. superba caused by C. fioriniae in the world, and its potential threat should be evaluated in the future. This study provided crucial information for epidemiologic studies and appropriate control strategies.

Molecular Characterization, Pathogenicity and Biological Characterization of Colletotrichum Species Associated with Anthracnose of Camellia yuhsienensis Hu in China

Camellia yuhsienensis Hu, a species of tea oil tree with resistance to anthracnose, is widely used to breed disease-resistant Camellia varieties. In 2019, anthracnose symptoms were observed on Ca. yuhsienensis for the first time. However, the species and biological characteristics of Colletotrichum spp. isolated from Ca. yuhsienensis (YX-Colletotrichum spp.) have not been elucidated. In this study, five isolates (YX2-5-2, 2YX-3-1, 2YX-5-1, 2YX-8-1-1 and 2YX-8-1-2), which were consistent with the morphological characteristics of Colletotrichum spp., were obtained from Ca. yuhsienensis. A phylogenetic analysis demonstrated that YX2-5-2, 2YX-3-1 and 2YX-8-1-2 belonged to first clade along with Colletotrichum fructicola. 2YX-8-1-1 belonged to the second clade along with Colletotrichum siamense. 2YX-5-1 belonged to the third clade with Colletotrichum camelliae. Pathogenicity tests revealed that the pathogenicity of YX-Colletotrichum spp. was stronger than that of Colletotrichum spp. isolated from Camellia oleifera (GD-Colletotrichum spp.). Biological characteristics illustrated that the mycelial growth of YX-Co. camelliae (2YX-5-1) was slower than that of GD-Co. camelliae when the temperature exceeded 20 °C. In addition, in the presence of ions, the mycelial growth of YX-Co. fructicola (YX2-5-2) and YX-Co. siamense (2YX-8-1-1) was also slower than that of GD-Co. fructicola and GD-Co. siamense. Furthermore, the ability of YX-Colletotrichum spp. to utilize lactose and mannitol was weaker than that of GD-Colletotrichum spp., while the ability to utilize NH4+ was generally stronger than that of GD-Colletotrichum spp. This is the first report of anthracnose of Ca. yuhsienensis induced by Co. fructicola, Co. siamense and Co. camelliae in China. These results will provide theoretical guidance for the study of the pathogenesis and control of anthracnose on Ca. yuhsienensis.

Pest categorisation of Colletotrichum fructicola

The EFSA Plant Health Panel performed a pest categorisation of Colletotrichum fructicola Prihast., a well-defined polyphagous fungus of the C. gloeosporioides complex which has been reported from all the five continents to cause anthracnose, bitter rot and leaf spotting diseases on over 90 cultivated and non-cultivated woody or herbaceous plant species. The pathogen is not included in EU Commission Implementing Regulation 2019/2072. Because of the very wide host range, this pest categorisation focused on Camellia sinensis, Citrus sinensis, C. reticulata, Fragaria × ananassa, Malus domestica, M. pumila, Persea americana, Prunus persica, Pyrus pyrifolia and P. bretschneideri for which there was robust evidence that C. fructicola was formally identified by morphology and multilocus gene sequencing analysis. Host plants for planting and fresh fruits are the main pathways for the entry of the pathogen into the EU. There are no reports of interceptions of C. fructicola in the EU. The pathogen has been reported from Italy and France. The host availability and climate suitability factors occurring in some parts of the EU are favourable for the establishment of the pathogen. Economic impact on the production of the main hosts is expected if establishment occurs. Phytosanitary measures are available to prevent the re-introduction of the pathogen into the EU. Although the pathogen is present in the EU, there is a high uncertainty on its actual distribution in the territory because of the re-evaluation of Colletotrichum taxonomy and the lack of systematic surveys. Therefore, the Panel cannot conclude with certainty on whether C. fructicola satisfies the criterium of being present but not widely distributed in the EU to be regarded as a potential Union quarantine pest unless systematic surveys for C. fructicola are conducted and Colletotrichum isolates from the EU in culture collections are re-evaluated.

First Report of Colletotrichum brevisporum Causing Soybean Anthracnose in China

In March 2020, widespread anthracnose was observed on soybean (Glycine max) in southeastern Jiangsu (Nantong municipality; 120.53° E, 31.58° N) in China. Plants exhibited irregular brown necrotic lesions in stem and leaves, and pronounced wilting. The symptoms were detected in one soybean field, 0.42 ha, surrounded by healthy wheat fields. Approximately 65% of the soybean plants showed the disease symptoms, and crop yield was reduced by 28-35% with respect the yield achieved in previous years, when no symptoms were observed. The symptoms were consistent with those previously reported for anthracnose on soybean caused by Colletotrichum chlorophyti, C. cliviae and C. gloeosporioides (Barbieri et al. 2017; Mahmodi et al. 2013; Yang et al. 2012). Diseased, 3-week old plants were collected. Small pieces, approximately 1 cm2 in size, of symptomatic tissue were surface sterilized in 1.5% NaOCl for 1 min, and washed twice with sterile ddH2O. The pathogen was isolated and cultured on potato dextrose agar (Song et al. 2020), containing chloramphenicol (50 µg/mL), under darkness at 28 °C for 3 days. Sequence of internal transcribed spacer (ITS), actin (ACT), β-tubulin (TUB2) and glyceraldehyde 3-phosphate dehydrogenase (GAP/span>DH) genes was performed as reported by Yang et al. (2015). Sequences were submitted to GenBank under accession numbers MT361074 (ITS) and MT415548-MT415550 (ACT, TUB2 and GAPDH). Blast search revealed that the amplified sequences had 100% (ITS; C. brevisporum TCHD, MH883805), 97.66% (ACT; C. brevisporum S38, KY986905), 99.06% (TUB2; C. brevisporum PF-2, KY705061) and 100% (GAPDH; C. brevisporum LJTJ27, KP823797) matches to multiple C. brevisporum strains, whereas all reported C. chlorophyti, C. cliviae and C. gloeosporioides strains showed no similarity to at least 2 of the studied genes. Molecular phylogenetic tree constructed using MEGA7 confirmed the identity of the pathogen. ACT and ITS sequences were blasted separately in Muscle (https://www.ebi.ac.uk/Tools/msa/muscle/) and then combined together to make the phylogenetic tree. The evolutionary history was inferred by using the Maximum Likelihood method based on the Tamura 3-parameter model, and the tree with the highest log likelihood (-1749.2186) is shown in Figure 1. The Colletotrichum strains previously found causing anthracnoseon soybean, and other relevant strains used in taxonomic analyses were included in the phylogenetic tree. Microscope observations showed the presence of 15-µm-long cylindrical conidia and septate mycelium, and agree with those reported for the morphology of C. brevisporum by Damm et al. (2019). To confirm pathogenicity, the mycelia from a 2 day-old culture on PDA was collected and suspended in sterile ddH2O (≈ 106 cells/mL) to prepare the inoculum. The pathogen was sprayed-inoculated on stem and leaves of healthy soybean plants. In control plants, sterile ddH2O was used. Inoculated plants were maintained in growth chamber at 28 °C and 50% relative humidity. Typical anthracnose symptoms were obsered 20 days after inoculation (Figure 2). C. brevisporum was reported to produce anthracnose on pumpkin, papaya, mulberry, coffee, passion fruit and pepper in China (Liu et al. 2017; Liu et al. 2019; Xue et al. 2019). Here, we report for the first time C. brevisporum causing anthracnose on soybean, an economically-relevant crop in China.

Characterization and Pathogenicity of Colletotrichum Species on Philodendron tatei cv. Congo in Gansu Province, China

In recent years in China, leaf spot caused by Colletotrichum species has been an emerging disease of Philodendron tatei cv. Congo. From 2016 to 2019, typical symptoms, appearing as circular or ovoid, sunken, and brown lesions with a yellow halo, were commonly observed on P. tatei cv. Congo in and around Lanzhou, Gansu Province, China. Conidiomata were often visible on infected leaf surfaces. Leaf disease incidence was approximately 5 to 20%. A total of 126 single-spored Colletotrichum isolates were obtained from leaf lesions. Multilocus phylogenetic relationships were analyzed based on seven genomic loci (ITS, ACT, GAPDH, HIS3, CAL, CHS-1, and TUB2) and the morphological characters of the isolates determined. These isolates were identified as three Colletotrichum species in this study. A further 93 isolates, accounting for 74% of all Colletotrichum isolates, were described as new species and named as Colletotrichum philodendricola sp. nov. after the host plant genus name, Philodendron; another two isolates were named as C. pseudoboninense sp. nov. based on phylogenetic and morphological relativeness to C. boninense; the other 31 isolates, belonging to the C. orchidearum species complex, were identified as a known species-C. orchidearum. Both novel species C. philodendricola and C. pseudoboninense belong to the C. boninense species complex. Pathogenicity tests by both spray and point inoculations confirmed that all three species could infect leaves of P. tatei cv. Congo. For spray inoculation, the mean infection rate of leaves on the three species was only 4.7% (0 to 12%), and the size on lesions was mostly 1 to 2 mm in length. For point inoculation, 30 days after nonwounding inoculation, the infection rate on leaves was 0 to 35%; in wounding inoculation, the infection rate of leaves was 35 to 65%; wounding in healthy leaves greatly enhanced the pathogenicity of these three species to P. tatei cv. Congo; however, the sizes of lesions among the three species were not significantly different. To our knowledge, this is the first report of Colletotrichum species associated with anthracnose diseases on P. tatei cv. Congo. Results obtained in this study will assist the disease prevention and appropriate management strategies.

Etiology of Cyclocarya paliurus Anthracnose in Jiangsu Province, China

Cyclocarya paliurus is an extremely valuable and multifunctional tree species whose leaves have traditionally been used in used in medicine or as a medicinal tea in China. In recent years, anthracnose has been frequently observed on young leaves of C. paliurus in several nurseries located in Jiangsu Province, resulting in great yield and quality losses. To date, no information is available about the prevalence of C. paliurus anthracnose in China. The main purpose of the present study was to characterize the etiology of C. paliurus anthracnose. Phylogenetic analysis of the eight-loci concatenated dataset revealed that all 44 single-spore Colletotrichum isolates belonged to three species in the Colletotrichum gloeosporioides species complex, namely, Colletotrichum aenigma, Colletotrichum fructicola, and C. gloeosporioides sensu stricto. Phenotypic features, including the colony appearance and the morphology of conidia, appressoria, and ascospores, were consistent with the phylogenetic grouping. Virulence tests validated that the three Colletotrichum species could cause typical symptoms of anthracnose on C. paliurus leaves, similar to those observed in the field. The optimum mycelial growth temperature ranged from 25 to 30°C for all representative isolates, while C. gloeosporioides s. s. isolates exhibited greater tolerance to high temperature (40°C). Fungicide sensitivity assays indicated that all three Colletotrichum species were sensitive to tetramycin, which may be a potential alternative for the management of C. paliurus anthracnose. To our knowledge, this study provides the first report of C. aenigma, C. fructicola, and C. gloeosporioides s. s. causing C. paliurus anthracnose in China as well as in the world.