Evaluation and Control of Alternaria tenuissima Causing Leaf Spots in Blue Honeysuckle in China

Blue honeysuckle is emerging as a popular edible fruit and is also used in folk medicine. However, from June to August 2021, a serious leaf-spot disease affected the yield and quality of blue honeysuckle in Harbin, Heilongjiang Province, China; the species and characteristics of the pathogens responsible for the disease were unknown. In this study, 30 fungal isolates were obtained from infected blue honeysuckle leaves and identified as Alternaria tenuissima based on morphological and molecular characteristics and phylogenetic analyses. To the best of our knowledge, this is one of the first studies to identify A. tenuissima as the causal agent of blue honeysuckle leaf spots in China. Pathogenicity tests of the isolates revealed that most isolates were moderately pathogenic. All blue honeysuckle cultivars tested were found to be susceptible to 30 A. tenuissima isolates. In addition, elder, Dahurian rose fruit, sea buckthorn, rowan, hawthorn, bird cherry, and sorb could be infected by A. tenuissima isolates, while European cranberry bush and Nanking cherry were not infected. A. tenuissima isolates were highly sensitive to prochloraz (EC50 ≤ 0.50 μg ml-1) with 86.21% efficacy at 400 μg ml-1 in the field trials. Therefore, crop rotation and application of chemical fungicides are considered to control the disease-causing leaf spots in blue honeysuckle. These results provide a basis for controlling A. tenuissima in blue honeysuckle in China.

Identification the Pathogen Cause a New Apple Leaf Blight in China and Determination the Controlling Efficacy for Five Botanical Fungicides

Alternaria leaf blight has recently been described as an emerging fungal disease of apple trees which is causing the significant damage in the apple-growing areas of Tianshui and Jingning, Gansu, China. In the present study, the pathogen species involved in apple leaf blight and its biological characteristics were identified, and the inhibitory activity of different botanical fungicides against the pathogen was evaluated in vitro. Four strains were isolated from the symptomatic areas of necrotic apple leaves, and initially healthy leaves showed similar symptoms to those observed in orchards after inoculation with the ABL2 isolate. The ABL2 isolate was identified as Alternaria tenuissima based on the morphological characteristics of its colonies, conidiophores, and conidia, and this was also confirmed by multi-gene sequence (ITS, OPA10-2, Alta-1, and endoPG) analysis and phylogenic analysis. The optimum temperature, pH, carbon source, and nitrogen source for the growth of A. tenuissima mycelia were 28 °C, 6-7, soluble starch, and soy flour, respectively. In addition, the botanical fungicide eugenol exhibited the highest inhibitory effect on the mycelial growth and conidia germination of A. tenuissima, and the median effective concentration (EC50) values were 0.826 and 0.755 μg/mL, respectively. The protective and curative efficacy of eugenol were 86.85% and 76.94% after inoculation in detached apple leaves at a concentration of 4 μg/mL. Our research provides new insights into the control of apple leaf blight disease by applying botanical fungicides.

Leaf Spot caused by Alternaria tenuissima on Rhamnella franguloides in China

The small tree species Rhamnella franguloides, belonging to the genus Rhamnella in the tribe Rhamneae Hook. f. of Rhamnaceae (Hauenschild et al. 2016), is an important medicinal plant commonly used for making tea in China. In August 2023, leaf spot symptoms were observed on R. franguloides in Shangyao county, Yantai, Shandong, China, with a disease incidence of 45-65%. Initially appearing as small dark brown spots on the tip lesions, they later expanded and merged into irregular-shaped brown necrotic lesions with yellowish halos. To isolate pathogen, 20 symptomatic tissue fragments (5 × 5 mm) from ten sampling randomly plants were surface sterilized, placed on potato dextrose agar (PDA) plates, and incubated at 25°C in darkness for 3 days to obtain colonies.10 purified isolates with similar morphological characteristics were obtained by single-spore isolation from the colonies. The representative isolate MR13 was chosen for morphological and molecular analysis. The colonies On PDA medium initially appear as a circular yellow-brown ring with white round margins, ultimately turning into olive green with fluffy aerial hyphae. The conidiophores displayed brown pigmentation, solitary or branched, producing abundant short chains of conidia. The conidia were typically obclavate to obpyriform or ellipsoid in shape, 22.5-64.5 × 12.5-23.6μm in size, with a short conical beak at the apex, zero to three longitudinal septa and one to five transverse septa. Based on cultural and morphological characteristics, the fungus was identified as Alternaria spp (Simmons 2007). Due to morphological traits, five genes (the internal transcribed spacer [ITS], actin [ACT], plasma membrane ATPase [ATP], Alternaria major allergen [Alt a1] and histone 3 [H3]) form MR13 were amplified using primer pairs ITSI / ITS4, ACTDF1/R1, ATPDF1 / ATPDRI, Alt-for / Alt-rev, and H3-1a/1b, respectively (Hong et al. 2005; Lawrence et al. 2013; Lousie and Donaldson 1995). BLASTn analysis failed to confirm the identification of MR13 species based on ITS, ACT, ATP and Alt a1(ITS, OR668512; ACT, OR676918; ATP, OR676917; Alt a1, OR676919). The phylogenetic tree showed that it was closely related to Alternaria alternate, A. tenuissima, and A. destruens. The H3 sequence (OR676920) exhibited 100% similarity to A. tenuissima (OR485421). The phylogenetic tree constructed solely with H3 further confirmed MR13 as A. tenuissima. Pathogenicity tests were conducted by introducing the fungus onto healthy R. franguloides leaves in the field. Fifty leaves (five per plant) were treated with a 20ml suspension containing around 1x10^4 spores/ml, while an equal number of control samples were sprayed with distilled water. Transparent plastic bags were used to cover the treated leaves for 48 hours and maintain humidity. After fourteen days of inoculation, consistent leaf spotting symptoms were observed. In contrast, the control leaves showed no sign of infection. The fungal pathogen was successfully reisolated and identified as A. tenuissima through morphological and sequence analysis, fulfilling Koch's postulates. To our knowledge, this is the first report of A. tenuissima causing leaf spot disease on R. franguloides in China. Identifying the disease's causal agent is crucial for developing effective management strategies.

Luobuma Leaf Spot Disease Caused by Alternaria tenuissima in China

Luobuma (Apocynum venetum and Poacynum hendersonni) is widely cultivated for environmental conservation, medicinal purposes and the textile industry. In 2018, a severe leaf spot disease that attacked the leaves of Luobuma was observed in plants cultivated in Yuzhong County, Gansu Province, China. Symptoms of the disease appeared as white or off-white spots surrounded by brown margins on the leaves of A. venetum. The spots expanded and covered a large area of the leaf, presenting as "cankers" with progression of the disease, leading to leaf death. The initial symptoms of the disease on P. hendersonni were similar to the symptoms of A. venetum, with a larger disease spot than A. venetum, and the spot was black and thicker. The aim of this study was to identify the fungal species and evaluate the effectiveness of fungicides (hymexazol and zhongshengmycin) against the pathogen in vitro. The fungi species that caused the new disease was identified as Alternaria tenuissima based on the morphological characteristics, pathogenicity tests, and phylogenetic analysis of the internal transcribed spacer (ITS) region, glyceraldehyde 3-phosphate dehydrogenase (gpd), translation elongation factor 1-alpha (TEF) and the histone 3 (H3) gene sequences. The findings showed that hymexazol fungicide can be used to control leaf spot disease. This is the first report on Luobuma leaf spot disease caused by A. tenuissima in China.

Cytotoxic Potential of Alternaria tenuissima AUMC14342 Mycoendophyte Extract: A Study Combined with LC-MS/MS Metabolic Profiling and Molecular Docking Simulation

Breast, cervical, and ovarian cancers are among the most serious cancers and the main causes of mortality in females worldwide, necessitating urgent efforts to find newer sources of safe anticancer drugs. The present study aimed to evaluate the anticancer potency of mycoendophytic Alternaria tenuissima AUMC14342 ethyl acetate extract on HeLa (cervical cancer), SKOV-3 (ovarian cancer), and MCF-7 (breast adenocarcinoma) cell lines. The extract showed potent effect on MCF-7 cells with an IC50 value of 55.53 μg/mL. Cell cycle distribution analysis of treated MCF-7 cells revealed a cell cycle arrest at the S phase with a significant increase in the cell population (25.53%). When compared to control cells, no significant signs of necrotic or apoptotic cell death were observed. LC-MS/MS analysis of Alternaria tenuissima extract afforded the identification of 20 secondary metabolites, including 7-dehydrobrefeldin A, which exhibited the highest interaction score (−8.0156 kcal/mol) in molecular docking analysis against human aromatase. Regarding ADME pharmacokinetics and drug-likeness properties, 7-dehydrobrefeldin A, 4’-epialtenuene, and atransfusarin had good GIT absorption and water solubility without any violation of drug-likeness rules. These findings support the anticancer activity of bioactive metabolites derived from endophytic fungi and provide drug scaffolds and substitute sources for the future development of safe chemotherapy.

Improving carboxymethyl cellulose edible coating using ZnO nanoparticles from irradiated Alternaria tenuissima

In this paper, gamma-irradiation was successfully used to intensify the yield of Zinc oxide nanoparticles (ZnONPs) produced by the fungus Alternariatenuissima as a sustainable and green process. The obtained data showed that 500 Gy of gamma-irradiation increased ZnONPs’ yield to approximately four-fold. The synthesized ZnONPs were then exploited to develop active Carboxymethyl Cellulose films by casting method at two different concentration of ZnONPs 0.5% and 1.0%. The physicochemical, mechanical, antioxidant, and antimicrobial properties of the prepared films were evaluated. The incorporation of ZnONPs in the Carboxymethyl Cellulose films had significantly decreased solubility (from 78.31% to 66.04% and 59.72%), water vapor permeability (from 0.475 g m⁻² to 0.093 g m⁻² and 0.026 g m⁻²), and oxygen transfer rate (from 24.7 × 10^–2 to 2.3 × 10^–2 and 1.8 × 10^–2) of the respective prepared films. Meanwhile, tensile strength (from 183.2 MPa to 203.34 MPa and 235.94 MPa), elongation (from 13.0% to 62.5% and 83.7%), and Yang's modulus (from 325.344 to 1410.0 and 1814.96 MPa) of these films were increased. Moreover, the antioxidant and antimicrobial activities against several human and plant pathogens the prepared of Carboxymethyl Cellulose-ZnONPs films were significantly increased. In conclusion, the prepared Carboxymethyl Cellulose-ZnONPs films showed enhanced activities in comparison with Carboxymethyl Cellulose film without NPs. With these advantages, the fabricated Carboxymethyl Cellulose-ZnONPs films in this study could be effectively utilized as protective edible coating films of food products.

First Report of Leaf Spot Caused by Alternaria tenuissima on Panicle Hydrangea (Hydrangea paniculata) in China

Panicle hydrangea (Hydrangea paniculata), belonging to the Saxifragaceae family (Wu et al. 2001), is an ornamental flowering plant which is native to China and Japan. In July 2021, brown leaf spots (diameter ranged from 3 to 5 mm) were observed on panicle hydrangea plants in a 0.1 ha field of Northeast Agriculture University (126.72°E, 45.74°N), Heilongjiang Province. The incidence was approximately 30%. Small circular or irregular brown spots initially appeared on the older leaves, and these lesions gradually expanded with time. In some serious cases, lesions joint together and caused leaf wilting. To identify the causal agent, ten symptomatic leaves from different panicle hydrangea plants were collected, and surface sterilized with 70% ethanol for 30 s, followed by 0.5% NaClO treatment for 4 min, and then rinsed with sterile water three times. Tissues between healthy and necrotic area were cut into 5×5 mm pieces after air drying on sterile filter paper. The pieces were placed on potato dextrose agar (PDA) amended with streptomycin sulfate (50 mg/liter) and incubated at 25°C for 5 days. Fifteen pure isolates were obtained using the hyphal tip technique and cultured on PDA for 7 days at 25°C for morphological and molecular identification. Colonies of all isolates were dark olivaceous with white margin. Conidiophores were septate, singly arising, and light brown, with a size range of 10.2-60.1 × 1.4-5.6 µm (n=50). Conidia were obclavate to obpyriform, brown to dark brown, and in a size range of 15.0-25.2 × 5.1-15.3 µm (n=50). To further identify these isolates, four different genomic DNA regions including ribosomal DNA internal transcribed spacer (ITS), glyceraldehyde-3-phosphate dehydrogenase (GAPDH), RNA polymerase II second largest subunit (rpb2), and histone 3 (HIS3) were amplified and sequenced with primers ITS1/ITS4 (White et al. 1990), gpd1/gpd2 (Berbee et al. 1999), RPB2-5F2/RPB2-7R (Sung et al. 2007), and H3-1a/H3-1b (Xu et al. 2022) for three representative isolates (DXQ2-2, DXQ2-3, and DXQ2-4), respectively. The sequences of ITS, GADPH, rpb2, and HIS3 for these three isolates were identical and only sequences of DXQ2-2 were deposited in GenBank (GenBank accession nos. OL305828, OL333601, OL333602, and OL436242). These sequences showed 100%, 100%, 100%, and 99.61% identity with A. tenuissima BJ-CX-1 (GenBank accession nos. MK683974, MK683784, MK684069, and MK683879), respectively. Based on morphological features and DNA sequences analyses, these isolates were identified as Alternaria tenuissima (Simmons 2007). To fulfill Koch's postulates, ten healthy and surface disinfected leaves of one panicle hydrangea plant grown in pot were sprayed with a conidial suspension (1×106 conidia/mL) of isolate DXQ2-2. Meanwhile, ten surface disinfected leaves of another panicle hydrangea plant grown in pot sprayed with sterilize water served as the control. All plants were maintained in a greenhouse at 25℃ and 70% relative humidity. Five days after inoculation, leaves inoculated with conidial suspension showed leaf spot symptoms that were similar to those observed in the field, whereas no symptom was observed on the control leaves. The experiment was conducted twice. The Alternaria tenuissima isolate was successfully re-isolated from the symptomatic leaves and confirmed based on above morphological and molecular methods. To our knowledge, this is the first report of leaf spot on panicle hydrangea caused by A. tenuissima. Leaf spot has a negative effect on the aesthetic value of panicle hydrangea, so further investigation and management is needed to control this disease.

Aggressiveness of Small-Spored Alternaria spp. and Their Sensitivity to Succinate Dehydrogenase Inhibitor Fungicides

Brown leaf spot of potato is caused by a number of small-spored Alternaria spp. Alternaria alternata sensu stricto, A. arborescens, and A. tenuissima have been reported with increasing frequency in commercial potato fields. Potato cultivars with resistance to small-spored Alternaria spp. have yet to be developed; therefore, the application of foliar fungicides is a primary management strategy. Greenhouse inoculation assays demonstrated that isolates of these three small-spored Alternaria spp. were pathogenic. Significant differences in aggressiveness were observed across isolates; however, there was no trend in aggressiveness based on species. Significant fungicide by isolate interactions in in vitro fungicide sensitivity and significant differences between baseline and nonbaseline isolates were observed in all three small-spored Alternaria spp. The ranges of in vitro sensitivity of A. alternata baseline isolates to boscalid (EC₅₀ <0.010 to 0.89 µg/ml), fluopyram (<0.010 to 1.14 µg/ml) and solatenol (<0.010 to 1.14 µg/ml) were relatively wide when compared with adepidyn (<0.010 to 0.023 µg/ml). The baseline sensitivities of A. arborescens and A. tenuissima isolates to all four fungicides were <0.065 µg/ml. Between 10 and 21% of nonbaseline A. alternata isolates fell outside the baseline range established for the four succinate dehydrogenase inhibitor (SDHI) fungicides evaluated. In A. arborescens, 10 to 80% of nonbaseline isolates had higher sensitivities than the baseline. A. tenuissima isolates fell outside the baseline for boscalid (55%), fluopyram (14%), and solatenol (14%), but none fell outside the baseline range for adepidyn. Evaluations of in vivo fungicide efficacy demonstrated that most isolates were equally controlled by the four SDHI fungicides. However, reduced boscalid efficacy was observed for four isolates (two each of A. arborescens and A. tenuissima) and reduced fluopyram control was observed in one A. alternata isolate. Results of these studies demonstrate that isolates of all three species could be contributing to the brown leaf spot pathogen complex and that monitoring both species diversity and fungicide sensitivity could be advantageous for the management of brown leaf spot in potatoes with SDHI fungicides.

First Report of Alternaria tenuissima Causing Leaf spot on Luffa cylindrica in China

In August 2020-2021, symptoms of leaf spot were observed in luffa (Luffa cylindrical) fields in Qingdao city, Shandong Province. In all the 10 fields investigated, leaf spot occurred. The incidence (% luffa plants with symptoms from a defined number of plants assessed) was 35 to 60%. Early symptoms of infected leaves were small and irregular chlorotic lesions which later became irregular brown spots. As the disease progressed, the lesions gradually spread from the edge to the center of leaves to the middle, and became dark brown. The enlarged spots coalesced and eventually led to the withering and death of the leaves. In order to isolate the pathogen, 30 symptomatic leaves were collected from different planting fields. Small pieces of leaf tissues (5×5 mm) were cut from the junction of healthy and diseased tissues, sanitized with 2% NaClO for 1 min, rinsed three times with sterile distilled water. The tissue samples were then placed on potato dextrose agar (PDA) amended with 50 mg/L streptomycin sulfate, and incubated at 28℃ for 5 days in the dark. Ten purified fungal isolates were obtained by single spore isolation method. Colonies of these fungal isolates on the PDA medium were initially grayish-white, and then turned olive green with abundant cotton-like aerial hyphae. On potato carrot agar (PCA) medium, these fungi produced light brown and solitary conidiophore with septum. Conidia were obclavate or ellipsoid, brown, with 1-5 transverse septa and 0-3 longitudinal septa, and measured 13.2 to 49.5 × 9.5 to 21.6 µm (n=50). The morphological characteristics of these isolates were consistent with that of Alternaria spp. (Simmons 2007). The representative isolate NEAU-SG-1 was selected for molecular identification. The internal transcribed spacer (ITS) region of ribosomal DNA, glyceraldehyde-3-phosphate dehydrogenase (GAPDH), translation elongation factor 1-α gene (TEF), histone 3 (HIS3), and RNA polymerase II second largest subunit (RPB2) were amplified using primer pairs ITS1/ITS4 (White et al. 1990), gpd1/gpd2 (Berbee et al. 1999), EF1-728F/EF1-986R (Carbone and Kohn 1999), H3-1a/H3-1b (Glass and Donaldson 1995), and RPB2-5F2/fRPB2-7cR (Sung et al. 2007), respectively. Sequences of these genes of isolate NEAU-SG-1 were deposited into GenBank database with the accession numbers of OL307719, OL415166, OL415169, OL415167, and OL415168. BLAST analysis of these sequences showed 99-100% homology with sequence homology with Alternaria tenuissima strains (ITS, MH824269; GAPDH, MK683783; TEF, MN056178; HIS3, MH824371; RPB2, LC621694). To fulfill Koch's postulates, ten surface disinfected 30-day-old luffa seedlings were inoculated by spraying conidia suspension (106 conidia/ml) of isolate NEAU-SG-1. The other ten surface disinfected seedlings inoculated with sterile distilled water served as the control group. After inoculation, each plant was covered with plastic bags for three days and cultured in greenhouse at 25℃. One week later, leaves inoculated with conidia suspension were observed with the same symptoms as described above, while the leaves of the control group were asymptomatic. Pathogenicity test was repeated twice. The Alternaria isolates were successfully re-isolated from those infected leaves and identified using the morphological and molecular methods described above. A. tenuissima has a wide host range in the world, and is the pathogen of leaf spot of many crops (Ma et al. 2021). To our knowledge, this is the first report of A. tenuissima causing leaf spot on luffa in China. This report will provide basic information for the diagnosis and prevention and control strategies of luffa leaf spot.

Co-Application of Tetramycin and Chitosan in Controlling Leaf Spot Disease of Kiwifruit and Enhancing Its Resistance, Photosynthesis, Quality and Amino Acids

Leaf spot disease caused by Lasiodiplodia theobromae and Alternaria tenuissima is a seriously fungal disease in kiwifruit production. In this study, the co-application of tetramycin and chitosan against leaf spot disease in kiwifruit and its effects on the disease resistance, photosynthesis, quality and amino acids of kiwifruit were investigated. The results show that tetramycin exhibited an excellent antifungal activity against L. theobromae and A. tenuissima with EC50 values of 2.37 and 0.16 mg kg−1. In the field, the foliar co-application of tetramycin and chitosan could effectively control leaf spot disease with control efficacy of 89.44% by spraying 0.3% tetramycin aqueous solutions (AS) 5000 time liquid + chitosan 100 time liquid, which was significantly (ANOVA, p < 0.01) higher than 79.80% of 0.3% tetramycin AS 5000 time liquid and 56.61% of chitosan 100 time liquid. Simultaneously, the co-application of tetramycin and chitosan was more effective than tetramycin or chitosan alone in enhancing the disease resistance and photosynthesis of kiwifruit leaves, as well as improving the quality and amino acids of kiwifruit fruits. This work highlights that chitosan is a practicable, cost-effective and eco-friendly adjuvant of tetramycin for controlling leaf spot disease of kiwifruit, enhancing resistance and photosynthesis of leaves and improving quality and amino acids of fruits.

Entomotoxic Activity of the Extracts from the Fungus, Alternaria tenuissima and Its Major Metabolite, Tenuazonic Acid

The study of fungal antibiotics in their competitive interactions with arthropods may lead to the development of novel biorational insecticides. Extracts of Alternaria tenuissima MFP253011 obtained using various methods showed a wide range of biological activities, including entomotoxic properties. Analysis of their composition and bioactivity allowed us to reveal several known mycotoxins and unidentified compounds that may be involved in the entomotoxic activity of the extracts. Among them, tenuazonic acid (TeA), which was the major component of the A. tenuissima extracts, was found the most likely to have larvicidal activity against Galleria mellonella. In the intrahaemocoel injection bioassay, TeA was toxic to G. mellonella and of Zophobas morio with an LT50 of 6 and 2 days, respectively, at the level of 50 µg/larva. Administered orally, TeA inhibited the growth of G. mellonella larvae and caused mortality of Acheta domesticus adults (LT50 7 days) at a concentration of 250 µg/g of feed. TeA showed weak contact intestinal activity against the two phytophages, Tetranychus urticae and Schizaphis graminum, causing 15% and 27% mortality at a concentration of 1 mg/mL, respectively. TeA was cytotoxic to the Sf9 cell line (IC50 25 µg/mL). Thus, model insects such as G. mellonella could be used for further toxicological characterization of TeA.

First Report of Alternaria tenuissima Causing Brown Spot Disease of Angelica dahurica in China

Angelica dahurica (Fisch. ex Hoffm.) is an abundantly cultivated Chinese herbal medicine plant in China with about 4000 hectares grown, the annual production is up to 24,000 tons. The medicinal part of A. dahurica is its root, and mainly function for treat cold, headache, toothache, rhinitis, diabetes, etc. Besides, A. dahurica is also used as a spice in Asia. In September 2018, brown spot was observed on the leaves of A. dahurica in fields of Anguo City, Hebei Province, China. In the field investigated, the incidence of brown spot disease reached 15%. The infected leaves showed brown spots surrounded with pale yellow edge, resulting in withered of the whole leaf. It seriously endangers the growth of A. dahurica, reducing the yield and quality of medicinal materials, even leading to the death of plants. We isolated the pathogen from 10 leaves with same lesions, the small square leaf pieces of approximately 3 to 5 mm were obtained with the sterile scissors from the junction of infected and healthy tissues, sterilized with sodium hypochlorite (10%) for 1 min followed by washing in sterile water for 3 times, then incubated on potato dextrose agar (PDA) plates at 25°C for 4 days. The culture was transferred to new PDA plates and was cultivated in dark at 25°C for 10 days. A total of 3 species of fungi were isolated, and only one fungus species has been found to be able to cause the original pathological characteristics of A. dahurica leaves through the back-grafting experiment. The mycelium was black and began to sporulate after 8 days on PDA media by single spore separation. Multiple spores joined together to form spores chain. The spores were spindle-shaped, yellow to yellow brown, and size ranged from 45 to 55 × 15 to 20 µm (n=50), with zero to three longitudinal septa and one to five transverse septa. For pathogenicity tests, the spore suspension (3.5×105 spores/mL) were inoculated to healthy plants grown in experimental field, the test was repeated four times, and 10 leaves were inoculated in each repetition, and the sterile water was inoculated as the blank control. Inoculated leaves were covered with transparent plastic bags for 24 h to keep humidity. Nine days later, it was found that there were lesions on the leaves inoculated with the pathogen, and the traits were the same as those in the field, while the controls are healthy. The fungus was consistently isolated from the inoculated leaves. The similar isolates were re-isolated from the inoculated and infected leaves and identified as Alternaria tenuissima by DNA sequencing, fulfilling Koch's postulates. Fungal genomic DNA was extracted from 7-day-old culture. PCR amplifications were performed using primers ITS1 / ITS4 and TEFF / TEFR respectively (Takahashi et al. 2006, Du 2008). The nucleotide sequence of PCR products, which have been deposited in Genebank under the accession numbers MN153514 and MN735428, showed 99.8%-100% identity with the corresponding sequences of A. tenuissima (MW194297 and MK415954). In order to further identify the pathogen species, we constructed a phylogenetic tree by combining TEF sequence and ITS sequence to distinguish the relationship between the pathogen and other minor species in the genus Alternaria, the isolate was clustered in the Alternaria clade. Therefore, the pathogen was identified as A. tenuissima based on the morphological characteristics and molecular identification. To our knowledge, this is the first report of A. tenuissima causing leaf spot on A. dahurica in China.

Leaf spot disease of Orychophragmus violaceus caused by Alternaria tenuissima in China

Orychophragmus violaceus (L.) O. E. Schulz, also called February orchid or Chinese violet cress, belongs to the Brassicaceae family and is widely cultivated as a green manure and garden plant in China. During the prolonged rainy period in August 2020, leaf spot disease of O. violaceus was observed in the garden of Northeast Agricultural University, Harbin, Heilongjiang province. One week after the rainy days, the disease became more serious and the disease incidence ultimately reached approximately 80%. The disease symptoms began as small brown spots on the leaves, and gradually expanded to irregular or circular spots. As the disease progressed, spots became withered with grayish-white centers and surrounded by dark brown margins. Later on, the centers collapsed into holes. For severely affected plants, the spots coalesced into large necrotic areas and resulted in premature defoliation. No conidiophores or hyphae were present, and disease symptoms were not observed on other tissues of O. violaceus. To isolate the pathogen, ten leaves with typical symptoms were collected from different individual plants. Small square leaf pieces (5×5 mm) were excised from the junction of diseased and healthy tissues, disinfected in 75% ethanol solution for 1 min, rinsed in sterile distilled water, and then transferred to Petri dishes (9 cm in diameter) containing potato dextrose agar (PDA). After 3 days of incubation at 25 oC in darkness, newly grown-out mycelia were transferred onto fresh PDA and purified by single-spore isolation. Nine fungal isolates (NEAU-1 ~ NEAU-9) showing similar morphological characteristics were obtained and no other fungi were isolated. The isolation frequency from the leaves was almost 90%. On PDA plates, all colonies were grey-white with loose and cottony aerial hyphae, and then turned olive-green and eventually brown with grey-white margins. The fungus formed pale brown conidiophores with sparsely branched chains on potato carrot agar (PCA) plates after incubation at 25 oC in darkness for 7 days. Conidia were ellipsoidal or ovoid, light brown, and ranged from 18.4 to 59.1 × 9.2 to 22.3 µm in size, with zero to two longitudinal septa and one to five transverse septa and with a cylindrical light brown beak (n = 50). Based on the cultural and morphological characteristics, the fungus was tentatively identified as Alternaria tenuissima (Simmons 2007). Genomic DNA was extracted from the mycelia of five selected isolates (NEAU-1 ~ NEAU-5). The internal transcribed spacer region (ITS) was amplified and sequenced using primers ITS1/ITS4 (White et al., 1990). Blast analysis demonstrated that these five isolates had the same ITS sequence, and the ITS sequence of representative strain NEAU-5 (GenBank accession No. MW139354) showed 100% identity with the type strains of Alternaria alternata CBS916.96 and Alternaria tenuissima CBS918.96. Furthermore, the translation elongation factor 1-α gene (TEF), RNA polymerase II second largest subunit (RPB2), and glyceraldehyde 3-phosphate dehydrogenase (GPD) of representative strain NEAU-5 were amplified and sequenced using primers EF1-728F/EF1-986R (Carbone and Kohn 1999), RPB2-5F2/RPB2-5R (Sung et al., 2007), and Gpd1/Gpd2 (Berbee et al., 1999), respectively. The sequences of RPB2, GPD, and TEF of strain NEAU-5 were submitted to GenBank with accession numbers of MW401634, MW165223, and MW165221, respectively. Phylogenetic trees based on ITS, RPB2, GPD, and TEF were constructed with the neighbour-joining and maximum-likelihood algorithms using MEGA software version 7.0. The results demonstrated that strain NEAU-5 formed a robust clade with A. tenuissima CBS918.96 (supported by 99% and 96% bootstrap values) in the neighbour-joining and maximum-likelihood trees. As mentioned above, strain NEAU-5 produced seldomly branched conidial chains on PCA plates. The pattern is consistent with that of A. tenuissima (Kunze) Wiltshire, but distinct from that of A. alternata which could produce abundant secondary ramification (Simmons 2007). Thus, strain NEAU-5 was identified as A. tenuissima based on its morphology and phylogeny. Pathogenicity tests were carried out by inoculating five unwounded leaves with a conidial suspension of strain NEAU-5 (approximately 106 conidia/ml) on five different healthy plants cultivated in garden, and an equal number of leaves on the same plants inoculated with sterilized ddH2O served as negative controls. Inoculated and control leaves were covered with clear plastic bags for 3 days. After 6 days, small brown and irregular or circular spots were observed on all leaves inoculated with conidial suspension, while no such symptoms were observed in the control. The tests were repeated three times. Furthermore, the pathogenicity tests were also performed using 2-month-old potted plants in a growth chamber (28 oC, 90% relative humidity, 12 h/12 h light/dark) with two repetitions. Five healthy plants were inoculated by spraying 20 ml of a conidial suspension of strain NEAU-5 (approximately 106 conidia/ml) onto unwounded leaves. Five other healthy plants were inoculated with sterilized ddH2O as controls. After 7 days, similar symptoms were observed on leaves inoculated with strain NEAU-5, whereas no symptoms were observed in the control. The pathogen was reisolated from the inoculated leaves and identified as A. tenuissima by morphological and molecular methods. In all pathogenicity tests, A. tenuissima could successfully infect unwounded leaves of O. violaceus, indicating a direct interaction between leaves and A. tenuissima. It is known that high humidity and fairly high temperatures can favor the epidemics of Alternaria leaf spot (Yang et al., 2018), and this may explain why severe leaf spot disease of O. violaceus was observed after prolonged rain. Previously, it has been reported that Alternaria brassicicola and Alternaria japonica could cause leaf blight and spot disease on O. violaceus in Hebei and Jiangsu Provinces, China, respectively (Guo et al., 2019; Sein et al., 2020). Although these pathogens could lead to similar disease symptoms on the leaves of O. violaceus, it is easy to distinguish them by the morphological characteristics of conidiophores and ITS gene sequences. To our knowledge, this is the first report of A. tenuissima causing leaf spot disease of O. violaceus in China.

First Report of Alternaria tenuissimain Causing Leaf Spot of Celery (Apium graveolens) in China

Celery (Apium graveolens) is one of the most widely grown vegetables in the world. A survey in Anding District of Gansu Province in 2019 showed that the incidence of celery leaf spot was 25%-45%. The disease mainly occurs in late June and July. The leaf spot is conducive to the onset at high temperature and humidity environment. The initial symptoms were many small light brown, irregular-shaped on the leaves. The lesions gradually enlarged in the later stage of the disease, and multiple lesions coalesced to form large irregular brown spots, eventually the whole leaves died. A 3~4mm leaf tissue was cut from the junction of the diseased leaf and the healthy area, the leaf tisse was surface-sterilized in 1.5% NaClO for 1 min and washed with sterile water. Then, it was incubated on potato dextrose agar (PDA) and obtained the pure culture (Q1). After 5 days of cultivation at 25°C, the fungal colonies were olivaceous to dark olive with white margins and abundant aerial mycelia. The conidia were obclavate or ellipsoid, pale brown, with 3~4 longitudinal septa and 2~7 transverse septa, and measured 20.0 to 50.0 × 3.5 to 14.0μm (n=50). Conidiophores were septate, arising singly, and measured 3.5 to 40.0 × 2.5 to 4.5 μm (n=50). Based on morphological characteristics, the fungus was preliminarily identified as A.tenuissima (Simmons 2007). To further confirm the identification, the internal transcribed spacer region (ITS), translation elongation factor 1-α gene (TEF), RNA polymerase II second largest subunit (RPB2), major allergen Alt a 1 gene (Alt a 1), endopolygalacturonase gene (endoPG), anonymous gene region (OPA10-2) and glyceraldehyde 3-phos-phatedehydrogenase (GAPDH) were amplified and sequenced using primers ITS1/ITS4 (Peever et al. 2004), EF1-728F/EF1-986R (Carbone et al. 1999), RPB2-5F2/RPB2-5R (Sung et al. 2007), Alt-for/Alt-rev (Hong et al. 2005), EPG-specific/EPG-3b (Peever et al. 2004), OPA10-2R/OPA10-2L (Peever et al. 2004) and Gpd1/Gpd2 (Berbee et al. 1999) (GenBank accession no.MN046364, MW016001, MW016002, MW016003, MW016004, MW016005, MW016006). DNA sequences of TEF, RPB2, endoPG, OPA10-2 and GAPDH were 100% identical to those of A. tenuissima (MN256108, MK605866, KP789503, JQ859829 and MK683802), but ITS and Alt a 1 were 100% similarity with A. tenuissima (MN615420, JQ282277) and A. alternate (MT626589, KP123847). The ITS and Alt a 1 sequence did not distinguish A. tenuissima from the A. alternate complex. Maximum likelihood phylogenetic analyses were performed for the combined data set with TEF, RPB2, and endoPG using MEGA6 under the Tamura-Nei model (Kumar et al. 2016). The isolate Q1 clustered with type strain A. tenuissima CBS 918.96. The 20 celery plants of 4-7 leaf age were used test the pathogenicity of Q1, the ten plants were sprayed with 20ml of spore suspension (1×105 spores/ml), the control was sprayed with 20mL sterile water, which were placed in a growth chamber (25℃, a 14h light and 10h dark period, RH > 80%). Eight days after inoculation, 40% of the leaves formed lesions, which were consistent with the field observation，the control group was asymptomatic. The pathogen was reisolated from infected leaves to fulfill Koch's postulates. To our knowledge, this is the first report of A. tenuissima causing leaf spot on celery in China.

First Report of Alternaria tenuissima Causing Leaf Blight on Sugarcane in China

Sugarcane (Saccharum officinarum L.) is the main sugar crop in China. Yunnan is the second largest sugarcane production province in China. In December 2018, leaf blight was first observed on almost every leaf of sugarcane on 'Huanan 54-11', 'Baimei' and 'Chongan' in Kaiyuan (103°27' E, 23°72' N), Yunnan. In October 2019, during our survey in the field in Lingcang (100°08' E, 23°88' N), Yunnan, this disease was also observed on 'ROC 25'. Symptoms of the disease initially appeared as wilted, which seemed to be cause by water stress. As the disease progressed, irregular straw-yellow and blighted lesion ran throughout the leaf lamina from leaf tip to entire leaf sheath, many small black conidia formed in the dead leaf tissue under humid conditions. Symptomatic leaf tissues were surface-sterilized with 70% ethanol for 30 s, 0.1% HgCl2 for 1 min, and rinsed with sterilized water three times, air dried on sterile filter paper, and plated on potato dextrose agar (PDA). Six isolates were obtained from six symptomatic leaf samples and were transferred onto potato carrot agar (PCA). Colonies on PDA were white with loose aerial hyphae at first, then turned to dark olive or dark. Colonies on PCA were grayish with sparse hyphae, then turned to dark gray. Conidiophores were brown, simple or branched, and produced numerous conidia in short chains. Conidia (n = 50) were obclavate to obpyriform or ellipsoid, brown to dark brown, with a cylindrical short beak at the tip (2.3 to 17.3 µm in length), and 15.3 to 46.6 μm × 4.2 to 17.9 μm, 2 to 7 transverse septa and 0 to 3 longitudinal septa. Morphologically, the isolates were identified as Alternaria tenuissima (Simmons 2007). Two representative isolates C4 and C5 were selected for molecular identification. The internal transcribed spacers (ITS), Histone 3 genes and plasma membrane ATPase were amplified with primer pairs ITS1/ITS4, H3-1a/H3-1b and ATPDF1/ATPDR1, respectively (Glass et al. 1995; Lawrence et al. 2013). The sequences were deposited in GenBank (ITS, MT679707-MT679708; Histone 3, MT710929-MT710930; ATPase, MT833928-MT833929). BLAST searches showed ≥99% nucleotide identity to the sequence of A. tenuissima (ITS, 100% to MN822571; Histone 3, 100% to MN481955; ATPase, 99% to JQ671875, 100% to MH492703, respectively). Thus, the fungus was identified as A. tenuissima based on morphological and molecular characteristics. For pathogenicity tests, five healthy 2-month-old potted sugarcane leaves were wounded with one sterile needle and inoculated with 20 μl of suspension of 106 conidia/ mL, and five plants were inoculated with distilled water as the controls. Plants were placed in a greenhouse at 25 to 35°C. After two months, the leaf wound inoculated with the putative pathogen displayed blighted as those observed in the field whereas the controls remained symptomless. The fungus was reisolated from symptomatic leaves with the same morphological and molecular traits as the original isolates. The fungus was not isolated from the control plants. Pathogenicity tests were repeated two times. A. tenuissima causing leaf blight on barley in China was reported in 2008 (Luo et al. 2008). Leaf spot disease of sugarcane caused by A. tenuis has been recorded in Maharashtra (Patil et al. 1974). To our knowledge, this is the first report on A. tenuissima affecting leaf blight on sugarcane in Yunnan Province, China. Identification of the causes of the disease is important to develop effective disease management strategies. The author(s) declare no conflict of interest. Funding: This research was supported by Sugar Crop Research System (CARS-170303), the Yunling Industry and Technology Leading Talent Training Program "Prevention and Control of Sugarcane Pests" (2018LJRC56), and the Yunnan Province Agriculture Research System. References: Glass, N. L., et al. 1995. Appl. Environ. Microbiol. 61:1323. Lawrence, D. P., et al. 2013. Mycologia 105:530. Luo, Z., et al. 2008. Acta Phytophy. Sin. 35(5): 469-470. Patil, A.O., et al. 1974. Res. J. Mahatma Phule Agric. Univ. 5(2): 122-123. Simmons, E. G. 2007. Alternaria: An Identification Manual. CBS Fungal Biodiversity Centre, Utrecht, The Netherlands. Caption for supplementary Figure 1 Supplementary Figure S1. Disease symptoms of sugarcane leaf blight disease and morphological characteristics of Alternaria tenuissima. (A) Typical straw-yellow and blighted lesions on naturally-infected leaves of sugarcane; (B) Infected symptoms on wounded leaves of sugarcane two months after artificial infection with A. tenuissima; (C) Colony of A. tenuissima on PDA; (D) Colony of A. tenuissima on PCA; and (E-F) Sporulation and conidia of A. tenuissima on PCA. (Scale bars = 100 μm; 20 μm).

Alternaria tenuissima Causing Leaf Spot Disease on Amygdalus triloba in Xinjiang of China

Amygdalus triloba (Rosaceae; previously Prunus triloba) is a deciduous, flowering shrub that is widely used in the greening and beautification of lawns, parks and courtyards in China. In late May 2019, a leaf spot disease of A. triloba was observed on approximately 35% of plants in the Xinjiang Alaer city (40˚33'20''N, 81˚17'19''E). The disease symptoms began as small, suborbicular, brown spots on the leaves. As the disease progressed, the spots enlarged and coalesced into large necrotic areas and resulted in premature defoliation. Leaf sections (5 x 5 mm) from infected leaves were surface - sterilized with 75% ethanol for 30 s and 0.1% HgCl2 for 1 min, rinsed three times in sterile distilled water and then incubated on potato dextrose agar (PDA). Fifteen fungal isolates showing similar morphological characteristics were obtained by single-spore isolation. On the PDA plates, all fungal colonies had a dark olive color with loose, cottony mycelium. On the potato carrot agar, the fungus formed unbranched spore chains, but occasionally formed one or two lateral branches. Conidiophores were short, hazel-colored, septae, arising singly, and measuring 15.1 to 61.8 × 1.8 to 4.2 µm (35.2 ± 1.4 × 2.3 ± 0.1 µm, n = 50). Mature conidia were ellipsoidal to ovoid with a short conical beak at the tip, light brown with zero to three longitudinal septa and one to five transverse septa, and measuring 19.3 to 30.8 × 7.2 to 12.5 µm (21.8 ± 0.3 × 9.5 ± 0.2 µm, n = 50). Based on the cultural and morphological traits, the pathogen was preliminary identified as Alternaria tenuissima (Simmons 2007). Genomic DNA was extracted from the representative isolate YALAR-1, and the internal transcribed spacer (ITS) region, the partial coding sequence of endopolygalacturonase (endoPG), the glyceradehyde -3- phosphate dehydrogenase (GAPDA), the partial region of the histone 3 (H3) genes were amplified using primers ITS1/ITS4 (White et al. 1990), PG2b/PG3a (Andrew et al. 2009), GDF1/GDR1 (Berbee et al. 1999) and H3-1a/H3-1b (Glass and Donaldson 1995), respectively. The amplicons were sequenced and deposited in GenBank [MT459807 (ITS), MT459808 (endoPG), MT459805 (GAPDA), MT459806 (H3)]. MegaBLAST analyses revealed that our ITS, endoPG, GAPDA, and H3 sequences were 99-100% identical to those of A. tenuissima isolates in GenBank [AF347032 (ITS), KP124026 (endoPG), AY278809 (GAPDA), KF997086 (H3)], confirming the identity of the pathogen as A. tenuissima. Pathogenicity tests were performed by inoculating the fungus onto healthy, mature leaves of A. triloba in the field. Twenty five leaves (five leaves/plant) were sprayed with spore suspensions (1 × 106 spores/ml) of each fungal pathogen, and the same number of leaves were sprayed with distilled water as controls. Inoculated and control leaves were covered with clear plastic bags for 3 days. The experiment was repeated three times. Twelve days after inoculation, the observed symptoms were similar to the original symptoms and the same fungal pathogen was reisolated from the inoculated leaves and identified as A. tenuissima based on morphological features and sequence analysis. The control leaves remained asymptomatic and no fungus was isolated from these leaves. Previously, a leaf spot of A. triloba caused by Alternaria brassicae was reported in Dalian, China (Xie et al. 2017). In order to control this disease effectively, further studies are needed on the biology and ecology of A. tenuissima and A. brassicae respectively. To our knowledge, this is the first report of A. tenuissima associated with leaf spot disease on A. triloba in China. In late September 2020, the diseased plant rate increased to 38% in Alaer city. If the disease control and prevention is neglected, the landscape of Alaer city will be affected seriously. So, in order to effectively control the spread of the disease, it is urgent now to study the sensitivity of pathogen to fungicide and carry out the field efficacy trials. References: Andrew, M., et al. 2009. Mycologia. 101:95. Berbee, M. L., et al. 1999. Mycologia. 91:964. Glass, N. L., and Donaldson, G. C. 1995. Appl. Environ. Microbiol. 61:1323. Simmons, E. G. 2007. Alternaria: An Identification Manual. CBS Fungal Biodiversity Centre, Utrecht, The Netherlands. White, T. J., et al. 1990. PCR Protocols: A Guide to Methods and Applications. Academic Press, San Diego, CA. Xie, Y., et al. 2017. Liaoning Agricultural Sciences. 6: 73.

First Report of Purple Spot on Dandelion in China Caused by Alternaria tenuissima

Dandelion (Taraxacum mongolicum) is a perennial herb of the family Asteraceae, with a high edible and medicinal value and widely grown at medium and low altitudes in China. In July 2019, purple spot of dandelion was found in a field near Harbin City, Heilongjiang province, China. The disease incidence regionally reached 95% in fields with yield losses between 10 and 20%, seriously reducing the economic and food value of dandelion. Multiple, irregular brown spots were first observed on the leaves of this plant- that later developed into circular or near-circular purple spots with raised centers, or purple lesions along the veins. When the leaf spots coalesced, the value of the commodity was lost. To isolate the pathogen, 5 × 5 mm pieces of leaf tissue from the margins of lesions were surface disinfected in 75% alcohol, rinsed in distilled water, and incubated on potato dextrose agar (PDA) plates at 28℃ until sporulation. Using single-spore isolation, a pure culture (YY-1) was obtained with abundant grayish white hyphae that later turned olive green. The underside of the colonies were brown. Conidia were typically obclavate, had a short beak with 1 to 6, but usually 3, transverse septa, and up to 3 longitudinal septa. The transverse septum was thicker and the wall of the conidium appeared brick-like. Conidia were pale brown, catenulate, and measured from 25 to 42 μm long by 6 to 10 μm wide. YY-1 was identified as Alternaria sp. based on morphological characteristics (Simmons 2007). Molecular identification was performed to detect the fungal species, and included the Internal Transcribed Spacer (ITS), translation elongation factor 1-alpha (EF1), actin gene (ACT), plasma membrane ATPase gene (ATP), and the calmodulin gene (CAL), which were respectively amplified with primers ITS4/ITS5 (Guo et al. 2012), EF1-728F/EF1-986R (Carbone and Kohn 1999), ACT-512F/ACT-783R (Carbone and Kohn 1999), and ATPDF1/ATPDR1 and CALDF1/CALDR1 (Lawrence 2013) (GenBank Accession Nos. MN746334, MT627208, MT627209, MT558864, MT558865). The species of Alternaria could not be confirmed by sequencing the above genes, as described previously (Zheng et al. 2015). Hence, a partial coding sequence of the histone 3 gene (GenBank Accession No. MN744235) was amplified using primers H3-1a/H3-1b (Zheng et al. 2015) and it shared 98.09% sequence identity with A. tenuissima (KP267543). The ITS sequence (MN746334) was 99.81% similar to the reference sequences of A. tenuissima (KT223327) in GenBank. A Maximum-likelihood tree was then reconstructed based on the ITS, CAL, and ATP sequences by MEGA7, which showed that YY-1 was most closely related to A. tenuissima. Therefore, YY-1 was identified as A. tenuissima based on its morphological and molecular characteristics. To perform Koch's postulates, 20 healthy leaves from greenhouse-grown dandelion were inoculated with 5-μL drops of a conidial suspension (1 x 105 conidia/ml) of isolate YY-1. Sterile water was used as a control. The inoculated plants were placed in a growth chamber at 28℃ and 80 to 90% relative humidity. After 10 days, similar symptoms were observed on plants inoculated with YY-1, while control plants did not produce symptoms. The pathogen was reisolated from the inoculated leaves and identified by morphological and molecular methods as A. tenuissima. To our knowledge, this is the first report of A. tenuissima causing purple spot on T. mongolicum in China.

Molecular and biological characterization of a novel strain of Alternaria alternata chrysovirus 1 identified from the pathogen Alternaria tenuissima causing watermelon leaf blight

The leaf blight caused by the genus Alternaria is one of the most epidemic diseases on watermelon, and A. tenuissima is the dominant pathogenic species in China. Mycoviruses are found ubiquitously in filamentous fungi, and an increasing number of novel mycoviruses infecting the genus Alternaria have been reported. In this study, a mycovirus from A. tenuissima strain SD-BZF-12 was identified and characterized, whose genome size was very similar with Alternaria alternata chrysovirus 1-N18 (AaCV1-N18). The dsRNA1- and dsRNA2-encoded proteins of the virus had 99 % identities with counterparts of AaCV1-N18; and the dsRNA3- and dsRNA4-encoded proteins of the virus showed the 80 % and 94 % sequence identities with proteins deduced from dsRNA4 and dsRNA3 of AaCV1-N18, respectively. Intriguingly, dsRNA5 of the virus encoded a truncated protein with 68 amino acids (aa) by comparing with 115 aa of AaCV1-N18 dsRNA5. Phylogenetic analysis of RNA-dependent RNA polymerase domain suggested that the virus clustered together with AaCV1-N18. Based on these characteristics, the mycovirus was identified to be a novel strain of AaCV1 and designated as AaCV1-AT1. In addition, no obvious differences were observed on colony morphology between AaCV1-AT1-infected and virus-cured strains of A. tenuissima; however, AaCV1-AT1 infection reduced colony growth rate and spore production ability on host fungus, and increased the median effective concentration of difenoconazole or tebuconazole on its host. This is the first report of AaCV1-AT1 associated with A. tenuissima.

Biosynthesis of zinc oxide nanoparticles with antimicrobial, anticancer, antioxidant and photocatalytic activities by the endophytic Alternaria tenuissima

AIMS

Zinc oxide nanoparticles (ZnONPs) were successfully synthesized using the culture filtrate of the endophytic fungus Alternaria tenuissima as a rapid, eco-friendly and cost-effective method.

METHODS AND RESULTS

The rapid synthesis of ZnONPs was completed after 20 min as confirmed by UV-Vis spectroscopy. The synthesized ZnONPs showed a single-phase crystalline structure. Dynamic light scattering analysis showed that the synthesized ZnONPs were monodispersed and the recorded polydispersity index value was 0·311. Zeta potential value of -23·92 mV indicated the high stability of ZnONPs. Transmission electron microscope revealed the spherical shape and the mean particle size was 15.45 nm. Functional groups present in the prepared samples of ZnONPs were confirmed by Fourier transform infrared spectroscopy. Additionally, the biological activities of in vitro antimicrobial, anticancer, antioxidant as well as the photocatalytic activities were evaluated. ZnONPs showed broad spectrum of antimicrobial potential against all the tested plant and human pathogens. Based on the MTT assay, ZnONPs inhibited the proliferation of normal human melanocytes, human breast and liver cancer cell lines with IC₅₀ concentrations of 55·76, 18·02 and 16·87 µg ml^-1 . ZnONPs exhibited promising antioxidant potential with 50% inhibitory concentration of 102·13 µg ml^-1 . Moreover, ZnONPs showed efficient degradation of methylene blue dye.

CONCLUSIONS

The synthesized ZnONPs showed promising activities that can be better explored in the near future for many medical, agricultural and industrial applications.

SIGNIFICANCE AND IMPACT OF THE STUDY

This study suggests a new and alternate approach with the excellent biotechnological potentiality for the production of ZnONPs which could open up the way for the industrial manufacture of nanoparticles using microbial platforms.

PlWRKY13: A Transcription Factor Involved in Abiotic and Biotic Stress Responses in Paeonia lactiflora

Many members of the WRKY family regulate plant growth and development. Recent studies have shown that members of the WRKY family, specifically WRKY13, play various roles in the regulation of plant stress resistance. To study the function of WRKY family members in peony, the PlWRKY13 gene (KY271095) was cloned from peony leaves. Sequence analysis and subcellular localization results revealed that PlWRKY13 has no introns, belongs to the type IIc subgroup of the WRKY family, and functions in the nucleus. The expression pattern of PlWRKY13 was analysed via real-time quantitative RT-PCR (qRT-PCR), which showed that the expression of PlWRKY13 was induced by four types of abiotic stress, low-temperature, high-temperature, waterlogging and salt stress, and was positively upregulated in response to these stresses. In addition, the expression of PlWRKY13 tended to first decrease and then increase after infection with Alternaria tenuissima. Virus-induced gene silencing (VIGS) technology was used to explore the function of PlWRKY13 in the resistance of Paeonia lactiflora to fungal infection further, and the results showed that PlWRKY13-silenced plants displayed increased sensitivity to A. tenuissima. The infection was more severe and the disease index (DI) significantly greater in the PlWRKY13-silenced plants than in the control plants, and the expression of pathogenesis-related (PR) genes was also significantly altered in the PlWRKY13-silenced plants compared with the control plants. The contents of the endogenous hormones jasmonic acid (JA) and salicylic acid (SA) were measured, and the results showed that the JA content increased gradually after infection with A. tenuissima and that JA may play an active role in the resistance of P. lactiflora to pathogen infection, while the SA content decreased after PlWRKY13 silencing. The contents of the two hormones decreased overall, suggesting that they are related to the transcription of PlWRKY13 and that PlWRKY13 may be involved in the disease-resistance pathway mediated by JA and SA. In summary, the results of our study showed that PlWRKY13 expression was induced by stress and had a positive effect on the resistance of P. lactiflora to fungal infection.

Chitosan induces resistance to tuber rot in stored potato caused by Alternaria tenuissima

Alternaria tenuissima infects stored potatoes, and causes tuber rot, resulting in significant economic losses. As a naturally-occurring polysaccharide (poly-β-(1 → 4) N-acetyl-D-glucosamine), chitosan has been reported to be an eco-friendly alternative to synthetic fungicides for the control of postharvest diseases on agricultural commodities. In this study, application of 0.25-1.25 g/L chitosan significantly inhibited spore germination and mycelial growth of A. tenuissima in vitro, with the greatest inhibitory effect observed at the highest concentration. Cytological and biochemical analysis of A. tenuissima spores indicated that exposure to 1.25 g/L chitosan significantly damaged the plasma membrane and increased the level of lipid oxidation. Gene expression analysis in potato tuber revealed that an application of 1.25 g/L chitosan induced the expression of defense-related genes, including catalase, peroxidase, polyphenol oxidase, chitinase and β-1,3-glucanase, and the level of flavonoids and lignin. Chitosan effectively controlled tuber rot caused by A. tenuissima. Collectively, results of the current study indicate that the ability of chitosan to reduce Alternaria rot in stored potato tubers is due to its direct antifungal activity and its ability to induce defense responses in potato tuber tissues. Chitosan may have the potential as a substitute for synthetic fungicides to reduce postharvest losses in potato.

The Population Genetics of Alternaria tenuissima in Four Regions of China as Determined by Microsatellite Markers Obtained by Transcriptome Sequencing

A total of 32,284 unigenes were obtained from the transcriptome of Alternaria tenuissima, a pathogenic fungus causing foliar disease in tomato, using next-generation sequencing (NGS) technology. In total, 24,670 unigenes were annotated using five databases, including NCBI non-redundant protein, Swiss-Prot, euKaryotic Orthologous Groups, Kyoto Encyclopedia of Genes and Genomes, and the Gene Ontology. A total of 1,140 simple sequence repeats were also identified for use as molecular markers. Sixteen of the simple sequence repeat loci were selected to study the population structure of A. tenuissima. A population genetic analysis of 191 A. tenuissima isolates, sampled from four geographic regions in China, indicated that A. tenuissima had a high level of genetic diversity, and that the selected simple sequence repeat markers could reliably capture the genetic variation. The null hypothesis of random mating was rejected for all four geographic regions in China. Isolation by distance was observed for the entire data set, but not within clusters, which is indicative of barriers to gene flow among geographic regions. The analyses of Bayesian and principal coordinates, however, did not separate four geographic regions into four separate genetic clusters. The different levels of historical migration rates suggest that isolation by distance did not represent a major biological obstacle to the spread of A. tenuissima. The potential epidemic spread of A. tenuissima in China may occur through the transport of plant products or other factors. The presented results provide a basis for a comprehensive understanding of the population genetics of A. tenuissima in China.

Production of paclitaxel with anticancer activity by two local fungal endophytes, Aspergillus fumigatus and Alternaria tenuissima

Among 60 fungal endophytes isolated from twigs, bark, and mature leaves of different plant species, two fungal isolates named TXD105 and TER995 were capable of producing paclitaxel in amounts of up to 84.41 and 37.92 μg L^-1, respectively. Based on macroscopic and microscopic characteristics, ITS1-5.8S-ITS2 rDNA sequence, and phylogenetic characteristic analysis, the two respective isolates were identified as Aspergillus fumigatus and Alternaria tenuissima. In the effort to increase paclitaxel magnitude by the two fungal strains, several fermentation conditions including selection of the proper fermentation medium, agitation rate, incubation temperature, fermentation period, medium pH, medium volume, and inoculum nature (size and age of inoculum) were tried. Fermentation process carried out in M1D medium (pH 6.0) and maintained at 120 rpm for 10 days and at 25 °C using 4% (v/v) inoculum of 5-day-old culture stimulated the highest paclitaxel production to attain 307.03 μg L^-1 by the A. fumigatus strain. In the case of the A. tenuissima strain, fermentation conditions conducted in flask basal medium (pH 6.0) and maintained at 120 rpm for 14 days and at 25 °C using 8% (v/v) inoculum of 7-day-old culture were found the most favorable to attain the highest paclitaxel production of 124.32 μg L^-1. Using the MTT-based assay, fungal paclitaxel significantly inhibited the proliferation of five different cancer cell lines with 50% inhibitory concentration values varied from 3.04 to 14.8 μg mL^-1. Hence, these findings offer new and alternate sources with excellent biotechnological potential for paclitaxel production by fungal fermentation.

Altertoxins with potent anti-HIV activity from Alternaria tenuissima QUE1Se, a fungal endophyte of Quercus emoryi

Screening of a small library of natural product extracts derived from endophytic fungi of the Sonoran desert plants in a cell-based anti-HIV assay involving T-cells infected with the HIV-1 virus identified the EtOAc extract of a fermentation broth of Alternaria tenuissima QUE1Se inhabiting the stem tissue of Quercus emoryi as a promising candidate for further investigation. Bioactivity-guided fractionation of this extract led to the isolation and identification of two new metabolites, altertoxins V (1) and VI (2) together with the known compounds, altertoxins I (3), II (4), and III (5). The structures of 1 and 2 were determined by detailed spectroscopic analysis and those of 3-5 were established by comparison with reported data. When tested in our cell-based assay at concentrations insignificantly toxic to T-cells, altertoxins V (1), I (3), II (4), and III (5) completely inhibited replication of the HIV-1 virus at concentrations of 0.50, 2.20, 0.30, and 1.50 μM, respectively. Our findings suggest that the epoxyperylene structural scaffold in altertoxins may be manipulated to produce potent anti-HIV therapeutics.

A new compound from an endophytic fungus Alternaria tenuissima

A new secondary metabolite, named altertoxin IV (1), together with altertoxin II (2), was isolated from the fermentation broth of Alternaria tenuissima, an endophytic fungal strain residing in the stem of Tribulus terrestris L. The structure of new compound 1 was established by HR-ESI-MS, multinuclear NMR spectroscopy, and single crystal X-ray diffraction method. In their in vitro bioassay, compound 2 exhibited moderate cytotoxic activity against PC-3 cell lines with an IC50 value of 14.28 μM.