Sorghum sheath blight caused by Fusarium spp. in Sinaloa, Mexico

Plant Disease ◽  
2021 ◽  
Author(s):  
Ruben Felix-Gastelum ◽  
Bertha Alicia Mora-Carlón ◽  
Karla Y. Leyva-Madrigal ◽  
Alma Rosa Solano-Baez ◽  
Juan Luis Pérez-Mora ◽  
...  
Keyword(s):  
Morphological Characteristics ◽  
Leaf Sheath ◽  
Sheath Blight ◽  
Control Measures ◽  
Field Conditions ◽  
Future Research ◽  
Fusarium Fujikuroi ◽  
Fusarium Spp ◽  
Stalk Rot ◽  
Fusarium Sp

Sorghum (Sorghum bicolor) leaf sheath blight was observed for the first time in Sinaloa, Mexico in the summer of 2020. Fungal isolates were obtained from symptomatic tissue in PDA. Fusarium spp. were associated with symptomatic plants in ten sampling sites under field conditions. No root and stalk rot were observed during the sampling period. Analysis of fragments of the EF-1a and RPB2 genes indicated that all isolates belong to the Fusarium fujikuroi species complex (FFSC). Five groups were delineated from this complex: F. thapsinum, F. verticillioides, Fusarium sp. (four isolates), Fusarium sp. (Fus4), and Fusarium sp. (Fus16), which is closely related to Fusarium madaense. The morphological characteristics (colony color and morphometry of conidia) of isolates with sequence similarities to those of F. thapsinum and F. verticillioides were in the expected range for these species. The morphology of isolates Fus7a, Fus7b, Fus11 and Fus17, as well as Fus4 and Fus16, were similar to those of the FFSC, specially to F. andiyazi and F. madaense. Inoculations of sorghum with representative isolates of F. thapsinum, F. verticillioides and the unidentified Fusarium species resulted in reddish brown lesions similar to those observed under field conditions; the original isolates inoculated were reisolated fulfilling the Koch's postulates. Although leaf sheaths on sorghum plants were heavily damaged, root and stalk rot were not observed in the greenhouse inoculations or under field conditions. Future research should focus on determining the identity of the unknown Fusarium spp. in order to design control measures of the disease. This is the first report of Fusarium spp. causing sorghum leaf sheath blight in Mexico.

scholarly journals Stem Rot Disease of Juglans sigillata Dode Caused by Fusarium fujikuroi in China

Plant Disease ◽  
2021 ◽  
Author(s):  
Shan Han ◽  
Yanyue Li ◽  
Ming Wang ◽  
Yiying Mo ◽  
Shujiang Li ◽  
...  
Keyword(s):  
Large Subunit ◽  
Apical Cell ◽  
Elongation Factor ◽  
Morphological Characteristics ◽  
Control Measures ◽  
Stem Rot ◽  
Fusarium Fujikuroi ◽  
Juglans Sigillata ◽  
Rot Disease ◽  
Juglans Sigillata Dode

Juglans sigillata Dode is an endemic species in the southwest China, and is an important nut and woody oil tree. The shell of its fruit is hard and can be used to make various crafts. From 216 to 2019, typical stem rot symptoms of 8-year-old J. sigillata were observed in cultivated fields in a 600-ha orchard in Zigong, Sichuan province, China. At this orchard, approximately 35% of the trees have been seriously damaged over the past few years. The typical symptoms were water-soaking on the stem, rotting, wilting, and blighting, eventually leading to the death of the plant. In June, ten diseased tissues were collected and surface-sterilized by 3% NaClO and 75% alcohol. Morphological observations were made from the isolates grown on Potato dextrose agar (PDA) and incubated at 25°C for 3 to 9 days. Morphological characteristics were made on pure cultures grown on Synthetic low nutrient agar (SNA). Five isolates with similar morphology were isolated from single spores. Colonies on PDA reached 8.3 cm in diameter after 6 days at 25 °C, aerial mycelia were white to cream and wol-like, later turning violet and dark purple with age. The hyphae of the strain were colorless and septate. There were two types of conidia on SNA, microconidia and macroconidia. Microconidia (n = 50) were oval, elliptic or clavate, no septate, 2.2 to 3.8 × 7.6 to11.7 μm. Conidiophores were branched or unbranched, solitary or in groups, phialides cylindrical to flask-shaped, monophialidic and polyphialidic. Macroconidia (n = 50) were long slender with a curved apical cell and foot-like basal cell, 3 to 4 septate and 2.1 to 3.9 × 26.2 to 53.4 μm. For molecular identification, the internal transcribed spacer (ITS), β-tubulin (TUB2), translation elongation factor (TEF1) and large subunit (LSU) were amplified with the corresponding primer pairs ITS1/ITS4 (White et al. 1990), BT2A/BT2B, EF1/EF2 (O’Donnell et al. 1997), and LROR/LR5 (Rehner and Samuels 1994), respectively. BLAST search results indicated that the ITS, TUB2, TEF1, LSU sequences (GenBank acc. nos. MT791384, MT786729, MN853324, and MT705246) showed 99 to100% identity with Fusarium fujikuroi sequences at NCBI (GenBank acc. nos. MG798789, MH398245, MK604519 and KJ954504). The results were confirmed by multilocus phylogenetic analysis. Based on the morphological characteristics and molecular analysis of the isolates, the fungus was identified as F. fujikuroi (Leslie and Summerell 2006). Koch’s postulates were checked under controlled conditions. Fifteen 2-year-old healthy potted J. sigillata were inoculated by pricking the epidermis of stem with a needle and applying 150 µl of a microconidial suspension (1 × 106 spores/ml) to the wounded surface with a brush. Sterilizd distilled water was used as the control. The experiment was repeated three times. All the plants were incubated at 25 ± 2°C after inoculation for daily observation of disease development. After 12 days, the inoculated plants showed the same symptoms as observed in the original diseased plants, while the control plants were asymptomatic. The fungus was re-isolated from the symptomatic stems and was completely identical to the isolates used to inoculate the plants. Thus, we confirmed that F. fujikuroi caused the stem rot of J. sigillata. To our knowledge, this is the first report of this fungus causing stem rot in J. sigillata in China. Our results can help identify stem rot disease of J. sigillata and develop control measures for the disease.

scholarly journals First Report of Fusarium temperatum Causing Seedling Blight and Stalk Rot on Maize in Spain

Plant Disease ◽  
2013 ◽  
Vol 97 (9) ◽  
pp. 1252-1252 ◽  
Author(s):  
C. Pintos Varela ◽  
O. Aguín Casal ◽  
M. Chaves Padin ◽  
V. Ferreiroa Martinez ◽  
M. J. Sainz Oses ◽  
...  
Keyword(s):  
Dna Sequences ◽  
Agar Medium ◽  
Fusarium Species ◽  
Morphological Characteristics ◽  
Gibberella Fujikuroi ◽  
Seedling Blight ◽  
Fusarium Spp ◽  
Potato Dextrose Agar Medium ◽  
Wheat Grains ◽  
Stalk Rot

In Europe, several diseases of maize (Zea mays L.) including seedling blight and stalk rot are caused by different Fusarium species, mainly Fusarium graminearum, F. verticillioides, F. subglutinans, and F. proliferatum (3). In recent years, these Fusarium spp. have received significant attention not only because of their impact on yield and grain quality, but also for their association with mycotoxin contamination of maize kernels (1,4). From October 2011 to October 2012, surveys were conducted in a maize plantation located in Galicia (northwest Spain). In each sampling, 100 kernels and 10 maize stalks were collected from plants exhibiting symptoms of ear and stalk rot. Dried kernels and small stalk pieces (1 to 2 cm near the nodes) were placed onto potato dextrose agar medium and incubated in the dark for 7 days. Fungal colonies displaying morphological characteristics of Fusarium spp. (2) were subcultured as single conidia onto SNA (Spezieller Nahrstoffarmer agar) (2) and identified by morphological characteristics, as well as by DNA sequence analysis. A large number of Fusarium species (F. verticillioides, F. subglutinans, F. graminearum, and F. avenaceum) (1,2) were identified. These Fusarium species often cause ear and stalk rot on maize. In addition, a new species, F. temperatum, recently described in Belgium (3), was also identified. F. temperatum is within the Gibberella fujikuroi species complex and is morphologically and phylogenetically closely related to F. subglutinans (2,3). Similar to previous studies (3), our isolates were characterized based on the presence of white cottony mycelium, becoming pinkish white. Conidiophores were erect, branched, and terminating in 1 to 3 phialides. Microconidia were abundant, hyaline, 0 to 2 septa; ellipsoidal to oval, produced singly or in false heads, and on monophialides, intercalary phialides, and polyphialides. Microconidia were not produced in chains. No chlamydospores were observed (3). Macroconidia in carnation leaf agar medium (2) were hyaline, 3 to 6 septate, mostly 4, falcate, with a distinct foot-like basal cell (2,3). DNA was amplified with primers ITS1/ITS4 and EF1/EF2 (3). Partial sequences of gene EF-1α showed 100% homology with F. temperatum (3) (GenBank Accession Nos. HM067687 and HM067688). DNA sequences of EF-1α gene and ITS region obtained were deposited in GenBank (KC179824, KC179825, KC179826, and KC179827). Pathogenicity of one representative isolate was confirmed using a soil inoculation method adapted from Scauflaire et al., 2012 (4). F. temperatum isolate was cultured on sterile wheat grains. Colonized wheat grains (10 g) were mixed with sterilized sand in 10 cm diameter pots. Ten kernels per pot were surface disinfected in 2% sodium hypochlorite for 10 min, rinsed with sterilized water, drained (4), placed on the soil surface, and covered with a 2 cm layer of sterilized sand. Five pots were inoculated and five uninoculated controls were included. Pots were maintained at 22 to 24°C and 80% humidity for 30 days. Seedling malformations, chlorosis, shoot reduction, and stalk rot were observed on maize growing in inoculated soil and not from controls. F. temperatum was reisolated from the inoculated seedlings but not from the controls. References: (1) B. J. Bush et al. Phytopathology 94:88, 2003. (2) J. F. Leslie et al. The Fusarium Laboratory Manual, page 388. Blackwell Publishing, 2006. (3) J. Scauflaire et al. Mycologia 103:586, 2011. (4) J. Scauflaire et al. Eur. J. Plant Pathol. 133:911, 2012.

COVID-19 Outbreak Prediction with Machine Learning

2020 ◽  
Author(s):  
Sina Faizollahzadeh Ardabili ◽  
Amir Mosavi ◽  
Pedram Ghamisi ◽  
Filip Ferdinand ◽  
Annamaria R. Varkonyi-Koczy ◽  
...  
Keyword(s):  
Machine Learning ◽  
Prediction Models ◽  
Fuzzy Inference ◽  
Control Measures ◽  
Future Research ◽  
Complex Nature ◽  
Inference System ◽  
Wide Range ◽  
Standard Models ◽  
High Level

Several outbreak prediction models for COVID-19 are being used by officials around the world to make informed-decisions and enforce relevant control measures. Among the standard models for COVID-19 global pandemic prediction, simple epidemiological and statistical models have received more attention by authorities, and they are popular in the media. Due to a high level of uncertainty and lack of essential data, standard models have shown low accuracy for long-term prediction. Although the literature includes several attempts to address this issue, the essential generalization and robustness abilities of existing models needs to be improved. This paper presents a comparative analysis of machine learning and soft computing models to predict the COVID-19 outbreak as an alternative to SIR and SEIR models. Among a wide range of machine learning models investigated, two models showed promising results (i.e., multi-layered perceptron, MLP, and adaptive network-based fuzzy inference system, ANFIS). Based on the results reported here, and due to the highly complex nature of the COVID-19 outbreak and variation in its behavior from nation-to-nation, this study suggests machine learning as an effective tool to model the outbreak. This paper provides an initial benchmarking to demonstrate the potential of machine learning for future research. Paper further suggests that real novelty in outbreak prediction can be realized through integrating machine learning and SEIR models.

scholarly journals Unequal impact of the COVID-19 crisis on minority ethnic groups: a framework for understanding and addressing inequalities

2021 ◽  
pp. jech-2020-216061
Author(s):  
Srinivasa Vittal Katikireddi ◽  
Sham Lal ◽  
Enitan D Carrol ◽  
Claire L Niedzwiedz ◽  
Kamlesh Khunti ◽  
...  
Keyword(s):  
Ethnic Groups ◽  
Social Consequences ◽  
Control Measures ◽  
Current Evidence ◽  
Future Research ◽  
Complex Interplay ◽  
Structural Racism ◽  
Theoretical Understanding ◽  
Minority Ethnic Groups ◽  
Minority Ethnic

Minority ethnic groups have been disproportionately affected by the COVID-19 pandemic. While the exact reasons for this remain unclear, they are likely due to a complex interplay of factors rather than a single cause. Reducing these inequalities requires a greater understanding of the causes. Research to date, however, has been hampered by a lack of theoretical understanding of the meaning of ‘ethnicity’ (or race) and the potential pathways leading to inequalities. In particular, quantitative analyses have often adjusted away the pathways through which inequalities actually arise (ie, mediators for the effect of interest), leading to the effects of social processes, and particularly structural racism, becoming hidden. In this paper, we describe a framework for understanding the pathways that have generated ethnic (and racial) inequalities in COVID-19. We suggest that differences in health outcomes due to the pandemic could arise through six pathways: (1) differential exposure to the virus; (2) differential vulnerability to infection/disease; (3) differential health consequences of the disease; (4) differential social consequences of the disease; (5) differential effectiveness of pandemic control measures and (6) differential adverse consequences of control measures. Current research provides only a partial understanding of some of these pathways. Future research and action will require a clearer understanding of the multiple dimensions of ethnicity and an appreciation of the complex interplay of social and biological pathways through which ethnic inequalities arise. Our framework highlights the gaps in the current evidence and pathways that need further investigation in research that aims to address these inequalities.

scholarly journals Characterization of Antagonistic Bacillus methylotrophicus Isolated From Rhizosphere and Its Biocontrol Effects on Maize Stalk Rot

2019 ◽  
Vol 109 (4) ◽  
pp. 571-581 ◽  
Author(s):  
Xingkai Cheng ◽  
Xiaoxue Ji ◽  
Yanzhen Ge ◽  
Jingjing Li ◽  
Wenzhe Qi ◽  
...  
Keyword(s):  
Biochemical Characterization ◽  
Disease Incidence ◽  
Field Trials ◽  
Control Measures ◽  
Disease Suppression ◽  
Effective Control ◽  
Stalk Rot ◽  
Bacillus Methylotrophicus ◽  
Transmission Electron ◽  
Potential Biocontrol Agent

Stalk rot is one of the most serious and widespread diseases in maize, and effective control measures are currently lacking. Therefore, this study aimed to develop a new biological agent to manage this disease. An antagonistic bacterial strain, TA-1, was isolated from rhizosphere soil and identified as Bacillus methylotrophicus based on morphological and biochemical characterization and 16S ribosomal RNA and gyrB gene sequence analyses. TA-1 exhibited a strong antifungal effect on the growth of Fusarium graminearum mycelium, with 86.3% inhibition at a concentration of 108 CFU per ml. Transmission electron microscopy showed that TA-1 could disrupt the cellular structure of the fungus, induce necrosis, and degrade the cell wall. Greenhouse and field trials were performed to evaluate the biocontrol efficacy of TA-1 on maize stalk rot, and the results of greenhouse experiment revealed that the bacterium significantly reduced disease incidence and disease index. Seeds treated with a 108 CFU ml−1 cell suspension had the highest disease suppression at 86.8%. Results of field trials show that seed bacterization with TA-1 could not only reduce maize stalk rot incidence but also increase maize height, stem diameter, and grain yield. The lipopeptide antibiotics were isolated from the culture supernatants of TA-1 and identified as surfactins and iturins. Consequently, B. methylotrophicus TA-1 is a potential biocontrol agent against maize stalk rot.

Skin as a Source of Nosocomial Infection: Directions for Future Research

1986 ◽  
Vol 7 (S2) ◽  
pp. 113-117 ◽  
Author(s):  
Dennis G. Maki
Keyword(s):  
Clinical Trials ◽  
Nosocomial Infection ◽  
Scientific Data ◽  
Control Measures ◽  
Future Research ◽  
Controlled Clinical Trials ◽  
Nosocomial Pathogens ◽  
The Past ◽  
Infection Control Measures ◽  
Per Se

Whereas infections of the skin per se comprise only a fraction of all institutionally-acquired infections, the skin has become one of the most important reservoirs of nosocomial pathogens in the hospital. Professor Noble has provided a scholarly review of the increasing importance of the major constituents of the cutaneous microflora as nosocomial pathogens and what we know of their epidemiology. Unfortunately, the empiricism and limited scientific data which underlie essential infection control measures in this area, particularly in regard to cutaneous antisepsis and handwashing, is almost incongruous in an era in which controlled clinical trials have dominated most other areas of medicine. The numerous outbreaks traced to contaminated antiseptics and disinfectants over the past two decades, stand as mute testimony to the inadequate investigative attention this area has received.

scholarly journals Current Classification and Diversity of Fusarium Species Complex, the Causal Pathogen of Fusarium Wilt Disease of Banana in Malaysia

Agronomy ◽  
2021 ◽  
Vol 11 (10) ◽  
pp. 1955
Author(s):  
Anysia Hedy Ujat ◽  
Ganesan Vadamalai ◽  
Yukako Hattori ◽  
Chiharu Nakashima ◽  
Clement Kiing Fook Wong ◽  
...  
Keyword(s):  
Fusarium Oxysporum ◽  
Fusarium Wilt ◽  
Species Complex ◽  
Phylogenetic Trees ◽  
Fusarium Species ◽  
Morphological Characteristics ◽  
Pathogenicity Test ◽  
Fusarium Spp ◽  
Specific Primers ◽  
Fusarium Oxysporum Species Complex

The re-emergence of the Fusarium wilt caused by Fusarium odoratissimum (F. odoratissimum) causes global banana production loss. Thirty-eight isolates of Fusarium species (Fusarium spp.) were examined for morphological characteristics on different media, showing the typical Fusarium spp. The phylogenetic trees of Fusarium isolates were generated using the sequences of histone gene (H3) and translation elongation factor gene (TEF-1α). Specific primers were used to confirm the presence of F. odoratissimum. The phylogenetic trees showed the rich diversity of the genus Fusarium related to Fusarium wilt, which consists of F. odoratissimum, Fusarium grosmichelii, Fusarium sacchari, and an unknown species of the Fusarium oxysporum species complex. By using Foc-TR4 specific primers, 27 isolates were confirmed as F. odoratissimum. A pathogenicity test was conducted for 30 days on five different local cultivars including, Musa acuminata (AAA, AA) and Musa paradisiaca (AAB, ABB). Although foliar symptoms showed different severity of those disease progression, vascular symptoms of the inoculated plantlet showed that infection was uniformly severe. Therefore, it can be concluded that the Fusarium oxysporum species complex related to Fusarium wilt of banana in Malaysia is rich in diversity, and F. odoratissimum has pathogenicity to local banana cultivars in Malaysia regardless of the genotype of the banana plants.

scholarly journals First Report of Powdery Mildew Caused by Golovinomyces biocellatus on Agastache rugosa in Korea

Plant Disease ◽  
2014 ◽  
Vol 98 (9) ◽  
pp. 1278-1278 ◽  
Author(s):  
S. E. Cho ◽  
J. H. Park ◽  
S. H. Hong ◽  
I. Y. Choi ◽  
H. D. Shin
Keyword(s):  
Powdery Mildew ◽  
Severe Disease ◽  
Morphological Characteristics ◽  
Control Measures ◽  
Control Treatment ◽  
Width Ratio ◽  
Korean Isolate ◽  
Pathogenicity Test ◽  
Agastache Rugosa ◽  
First Report

Agastache rugosa (Fisch. & C.A. Mey.) Kuntze, known as Korean mint, is an aromatic plant in the Lamiaceae. It is widely distributed in East Asian countries and is used as a Chinese traditional medicine. In Korea, fresh leaves are commonly added to fish soups and stews (3). In November 2008, several dozen Korean mints plants growing outdoors in Gimhae City, Korea, were found to be severely infected with a powdery mildew. The same symptoms had been observed in Korean mint plots in Busan and Miryang cities from 2008 to 2013. Symptoms first appeared as thin white colonies, which subsequently developed into abundant hyphal growth on stems and both sides of the leaves. Severe disease pressure caused withering and senescence of the leaves. Voucher specimens (n = 5) were deposited in the Korea University Herbarium (KUS). Appressoria on the mycelium were nipple-shaped or nearly absent. Conidiophores were 105 to 188 × 10 to 13 μm and produced 2 to 4 immature conidia in chains with a sinuate outline, followed by 2 to 3 cells. Foot-cells of the conidiophores were straight, cylindrical, slightly constricted at the base, and 37 to 58 μm long. Conidia were hyaline, ellipsoid to barrel-shaped, measured 25 to 40 × 15 to 23 μm (length/width ratio = 1.4 to 2.1), lacked distinct fibrosin bodies, and showed reticulate wrinkling of the outer walls. Primary conidia were obconically rounded at the apex and subtruncate at the base. Germ tubes were produced at the perihilar position of conidia. No chasmothecia were observed. The structures described above were typical of the Oidium subgenus Reticuloidium anamorph of the genus Golovinomyces. The measurements and morphological characteristics were compatible with those of G. biocellatus (Ehrenb.) V.P. Heluta (1). To confirm the identification, molecular analysis of the sequence of the internal transcribed spacer (ITS) region of ribosomal DNA (rDNA) of isolate KUS-F27200 was conducted. The complete ITS rDNA sequence was amplified using primers ITS5 and P3 (4). The resulting 514-bp sequence was deposited in GenBank (Accession No. KJ585415). A GenBank BLAST search of the Korean isolate sequence showed >99% similarity with the ITS sequence of many G. biocellatus isolates on plants in the Lamiaceae (e.g., Accession Nos. AB307669, AB769437, and JQ340358). Pathogenicity was confirmed by gently pressing diseased leaf onto leaves of five healthy, potted Korean mint plants. Five non-inoculated plants served as a control treatment. Inoculated plants developed symptoms after 7 days, whereas the control plants remained symptomless. The fungus present on inoculated plants was identical morphologically to that observed on the original diseased plants. The pathogenicity test was repeated with identical results. A powdery mildew on A. rugosa caused by G. biocellatus was reported from Romania (2). To our knowledge, this is the first report of powdery mildew caused by G. biocellatus on A. rugosa in Korea. The plant is mostly grown using organic farming methods with limited chemical control options. Therefore, alternative control measures should be considered. References: (1) U. Braun and R. T. A. Cook. Taxonomic Manual of the Erysiphales (Powdery Mildews), CBS Biodiversity Series No. 11. CBS, Utrecht, 2012. (2) D. F. Farr and A. Y. Rossman. Fungal Databases. Syst. Mycol. Microbiol. Lab., online publication, USDA ARS, retrieved 17 February 2014. (3) T. H. Kim et al. J. Sci. Food Agric. 81:569, 2001. (4) S. Takamatsu et al. Mycol. Res. 113:117, 2009.

scholarly journals First Report of Pythium aphanidermatum Causing Stalk Rot on Abelmoschus manihot (L. ) Medic in China

Plant Disease ◽  
2021 ◽  
Author(s):  
Qing Qu ◽  
Liu Shiwei ◽  
Ning Liu ◽  
Yunxia Liu ◽  
Jia Hui ◽  
...  
Keyword(s):  
Management Practices ◽  
Vascular System ◽  
Morphological Characteristics ◽  
Pythium Aphanidermatum ◽  
Negative Control ◽  
Perennial Herb ◽  
Universal Primers ◽  
First Report ◽  
Stalk Rot ◽  
Aerial Hyphae

Abelmoschus manihot (Linn. ) Medicus (A. manihot) is an annual to perennial herb of the Malvaceae okra, mainly distributed in Guangdong, Guangxi, Fujian, Hunan, Hubei provinces. It can not only be used as an ornamental flower, but also has important economic and medicinal value. Last year, 10% A. manihot in 1,000 acres were observed with stalk rot in the Zhongshang Agricultural Industrial Park, 50 meters east of Provincial Highway 235 in Gaoyang County of Hebei province. Internal discoloration of the stem began brown to black discoloration of the vascular system and became hollow, with the mycelium growing on the surface. Stems from symptomatic plants (approximately 5 mm2) were dissected, washed free of soil, then soaked in 75% ethanol for 16 s to surface-sterilize, and 40 s in HgCl2, then rinsed three times in sterile water. After being dried with blotting paper, five pieces were placed on potato dextrose agar (PDA). After cultured 2 or 3 days, five isolates were purified and re-cultured on PDA in the dark at 25°C. The color of the colony was white. The hyphae were radial in PDA, and the aerial hyphae were flocculent, well-developed with luxuriant branches. The colonies were white and floccus, and the aerial hyphae were well developed, branched and without septum on corn meal agar (CMA). The sporangia were large or petal shaped, composed of irregular hyphae, terminal or intermediate , with the size of (31.6-88.4) μm ×(12.7- 14.6) μm. Vesicles were spherical, terminal or intermediate, ranging from 14.6 to 18.5μm. Oogonia were globose, terminal and smooth which stipe was straight. Antheridia were clavate or baggy and mostly intercalary, sometimes terminal. Oospores were aplerotic, 21.5 to 30.0 μm in diameter, 1.6 to 3.1 μm in wall thickness. The isolates morphological characteristics were consistent with P. aphanidermatum (van der Plaats-Niterink 1981, Wu et al. 2021 ). To identify the isolates, universal primers ITS1/ITS4 (White et al. 1993) were used for polymerase chain reaction–based molecular identification. The amplification region was sequenced by Sangon Biotech (Shanghai, China) and submitted to GenBank (MW819983). BLAST analysis showed that the sequence was 100% identical to Pythium aphanidermatum. Pathogenicity tests were conducted 3 times, with 4 treatments and 2 controls each time. The plants treated were 6 months old. Then the hyphae growing on PDA for 7 days were cut into four pieces. Next, they were inoculated into the soil of the A. manihot. Negative control was inoculated only with PDA for 7 days ( Zhang et al. 2000). The plants were then placed in a greenhouse under 28°C, 90% relative humidity. After inoculated 20 to 30 days, the infected plants showed stalk rot, the same symptoms as observed on the original plants. The control plants didn’t display symptoms. Pythium aphanidermatum was re-isolated from infected stems and showed the same characteristics as described above and was identical in appearance to the isolates used to inoculate the plants. To our knowledge, this is the first report of Pythium aphanidermatum infecting A. manihot stem and causing stalk rot in China. It may become a significant problem for A. manihot. Preliminary management practices are needed for reducing the cost and losses of production.

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