First Report of Black Spot Caused by Neoscytalidium dimidiatum on Sisal in Guangxi, China

Abstract

Sisal (Agave sisalana Perrine) is an important hard fiber crop that is widely planted in Guangxi, Guangdong, Hainan, Yunnan, and Fujian provinces, China. In July 2019, a new leaf disease of sisal with a disease incident of about 36% was found in Guangxi (Fig.1a~d). The oval or circular black lesions were 2.3 cm to 15.9 cm in length and 1.6 cm to 5.5 cm in width on both sides of the diseased leaves. The central part of the lesions was slightly hollow. The lesions continuously enlarged and ultimately penetrated the leaves. Reddish brown and dark mucus was secreted from the lesions. The junction of lesions and healthy parts was reddish brown to yellow. The diseased leaf fiber and mesophyll tissues were reddish brown and necrotic. Fresh leaf yield was reduced about 30% by the disease, and fiber quality was significantly compromised every year in Guangxi. Six kinds of fungi distinguished by their morphology, size and color of the colonies were isolated from diseased leaf tissues of 60 sisal plants sampled from five different farms in Guangxi. Isolate JMHB1 was isolated at a rate of 95.67%. The isolate JMHB1 was initially white with dense and hairy aerial mycelium, gradually turning dark grey to olive green on PDA (Fig. 2). Conidia, arthrospores, and chlamydospores were observed on PDA in culture (Fig. 3). The conidia formed arthric chains, disarticulating, cylindrical-truncate, oblong-obtuse to doliiform, colorless and transparent, zero- to one-septate, and averaging 4.4 to 13.8 µm × 2.2 to 5.6 µm (n=100). Arthrospores were short columnar, pigmented and transparent, single or formed arthric chains, averaging 5.5 to 17.9 µm × 2.1 to 3.5 µm (n=100). Chlamydospores were dark brown, round or oval, averaging 4.5 to 9.6 µm × 4.5 to 8.6 µm (n=100). Pathogenicity testing was conducted by inoculating 3-year-old healthy sisal plants with PDA plugs (5 × 5 mm) on which the fungus had grown for 5 days. Nine healthy plants were wounded on the leaves with a sterile needle, and mycelial plugs were placed on the wounds, covered with sterile moist cotton, and wrapped with parafilm. Nine control plants were wounded and treated with PDA plugs as the negative control. The test was repeated three times. All treated plants were kept in a greenhouse at ~28 ℃ and 40% RH. After 5 days, only leaves inoculated with isolate JMHB1 showed lesions similar to symptoms observed in the field (Fig.1e~f). The fungus was re-isolated from all nine diseased plants, and no symptoms were observed on the leaves of control plants. Molecular identification of the fungus was made by PCR amplification of the internal transcribed spacer (ITS) region of rDNA, EF1-α gene and β-tubulin gene using primers ITS1/ITS4 (White et al. 1990), EFl-728F/EF1-986R (Carbone and Kohn 1999), TUB2Fd/TUB4Rd (Aveskamp et al. 2009) respectively. The ITS (MT705646), EF1-α (MT733516) and β-tubulin (MT773603) sequences of JMHB1 were similar to the ITS (AY819727), EF1-α (EU144063) and β-tubulin (KF531800) sequences of the epitype of Neoscytalidium dimidiatum (CBS 499.66) with 100%, 99.65% and 99.02% identity, respectively. Based on pathogenicity testing, morphological characteristics, and molecular identification, the pathogen of sisal causing black spot was identified as N. dimidiatum (Penz.) Crous & Slippers (Crous et al. 2006). To our knowledge, this is the first report of black spot caused by N. dimidiatum on sisal in China. Sisal is the main economic crop in arid and semi-arid areas that is widely planted in several provinces of southern China. The serious occurrence of the disease caused by N. dimidiatum has greatly affected the development of sisal industry and local economic income in China. Identification of the pathogen of the disease is of great significance to guide disease control, increase farmers' income and promote the development of sisal industry. References: Aveskamp, M. M., et al. 2009. Mycologia, 101: 363. https://doi.org/10.3852/08-199. Carbone, I., and Kohn, L. M. 1999. Mycologia, 91:553. https://doi.org/10.1080/00275514.1999. 12061051. Crous, P. W., et al. 2006. Stud. Mycol. 55:235. https://doi.org/10.3114/sim.55.1.235. White, T. J., et al. 1990. PCR Protocols: A Guide to Methods and Applications. Academic Press, San Diego, Page 315. doi.org/10.1002/mrd.1080280418. Supplemental photographs: Fig. 1 Symptoms of sisal black spot disease a, b, c, d showed symptoms in the field, e and f were symptoms after inoculating Neoscytalidium dimidiatum JMHB1. a, c, and e were the front of the lesions, b, d, and f were the back of the lesions. Fig. 2 Primary colony (a) and old colony (b) of Neoscytalidium dimidiatum JMHB1 Fig. 3 Arthrospores (a), conidia and chlamydospores (b) of Neoscytalidium dimidiatum JMHB1

Pest categorisation of Neoscytalidium dimidiatum

“…The pathogen is most likely to survive on infected dead plant organs (Moral et al., 2019 ) and on plant debris in the soil mainly in the form of mycelium and pycnidia, similarly to other members of the family Botryosphaeriaceae (Sakalidis et al., 2011 ). No sexual stage has been reported so far and production of survival structures (chlamydospores) by the pathogen has been observed only in pure cultures (Xie et al., 2021 ).…”

“… Fabaceae Acacias Chandra ( 1974 ) Albizia lebbeck Fabaceae Siris tree Elshafie and Ba‐Omar ( 2002 ) Agave sp. Asparagaceae Kranz ( 1963 ) Agave sisalana Asparagaceae Sisal Xie et al ( 2021 ) Anacardium occidentale Anacardiaceae Cashew Coutinho et al ( 2018 ) Ananas comosus Bromeliaceae Pineapple Kuruppu et al ( 2021 ) Arachnis sp. Orchidaceae Scorpion orchid Williams and Liu ( 1976 ) Araucaria sp.…”

Development of a Specific Nested PCR Assay for the Detection of 16SrI Group Phytoplasmas Associated with Sisal Purple Leafroll Disease in Sisal Plants and Mealybugs

“…is the most important hard fibre crop in the world [ 1 ]. Unfortunately, worldwide, it is infected by numerous fungal pathogens, including Aspergillus welwitschiae [ 1 ], Phytophthora nicotianae [ 2 ], and Neoscytalidium dimidiatum [ 3 ], and it is infested by insects such as Dysmicoccus neobrevipes [ 4 ] and Scyphophorus acupunctatus [ 5 ]. Purple leafroll disease (SPLD) is currently the most destructive disease affecting sisal in China.…”

A review of research trends on Nattrassia mangiferae from 1966-2022: A bibliometric approach

“…The distribution of this genus has extended to all continents. Neoscytalidium genus can influence the different parts of plants by causing diseases that show various symptoms on aerial and underground parts of hosts, including shoot blight canker and gummosis (Polizzi et al, 2009), dieback (Ray et al, 2010), collar and root rot (Machado et al, 2012), brown spot (Lan et al, 2012), death of graft (Chen et al, 2013), internal black rot (Ezea et al, 2013), shoot and needle blight (Türkölmez et al, 2019a), tuber rot (Derviş et al, 2020a), root and stem rot (Oksal and Ozer, 2021;Kuruppu et al, 2021), stem-end rot (Li et al, 2021), sooty canker (Yeganeh and Mohammadi, 2022), and leaf scorch (Table 1). Members in the genus Neoscytalidium have been reported as pathogenic agents on various crops and trees, such as almond (Prunus dulcis), Avicennia marina Forssk., baobab (Adansonia gibbosa), bardi bush (Acacia synchronica), blue grevillea (Grevillia agrifolia), rattlepod (Crotalaria medicaginea), olive (Olea europaea L.), etc.…”