First Report of Neoscytalidium dimidiatum causing leaf zonate spot disease of Aloe vera L. in China.

In February 2022, leaf zonate spot disease afflicted Aloe vera L. in Yunnan, China, endangering the $39 billion industry with 0.33ha under cultivation (Wan 2015). The disease manifested with watery spots progressing into oval or circular necrosis lesions, characterized by a dark center surrounded by a gray-brown zone. In the late stage of the disease, lesions regress in size and several small dark picnidia dots appeared on the gray-brown zone. The disease incidence ranged from 10% to 15% in three commercial plantations. If left uncontrolled, the disease could diminish the commercial value of Aloe vera plants. Eighteen symptomatic leaf samples underwent morphological and genetic identification. The samples were carefully washed with distilled water and 1×1 cm2 sections of tissue were excised using a sterile scalpel. The sections underwent surface-disinfection with 3% NaOCl for 3 min and 75% ethanol for 30 s. After three sterile water rinses the sections were air-dried. Subsequently, they were transferred to potato dextrose agar (PDA) before being incubated at 25 ℃ in the dark. Of the 18 samples, eight produced the colonies with similar morphological characteristics, named LH7. Isolate LH7 had downy to woolly aerial mycelia, initially pinkish white on the surface, and gradually turned greenish-olivaceous from the middle, and eventually turned dark brown to black after seven days. The fungus formed arthric chains in the aerial mycelium on PDA but did not produce conidiomata. The conidia, which occurred in arthric chains were 5.50-9.9 × 4.08-7.51 µm (mean 7.09× 5.26 µm, n=50) in size, cylindrical, brown, and 0-1 septate. To ascertain LH7's pathogenicity, three healthy one-year old aloe plants were surface-sanitized with a 1% aqueous chlorine solution, rinsed with sterile water, and dried. Three leaves from each plant were punctuated and inoculated using conidial suspension (100 µl of 1x 106 conidial mL-1), while three control plants were inoculated with sterile distilled water. The pathogenicity tests were repeated twice. The inoculated plants were kept at 25 ℃ with a 12-hour light/12-hour dark cycle. After seven days, symptoms observed in the field appeared in the plants, while no disease occurred in the control plants. After 21 days, conidiomata formed on the inoculated leaves, averaging 116.92 µm (n=20) in diameter. These conidiomata were globose to subglobose, and brown to sub-brown. The fungus was successfully re-isolated from symptomatic tissue and the resulting colonies were morphologically consistent with isolate LH7. Based on the characteristics, the fungus was identified as Neoscytalidium dimidiatum (Philips et al. 2013). The specimen was deposited in China Center for Type Culture Collection ( CCTCC AF 2024001). This identification was confirmed through sequencing of ITS gene region of rDNA using ITS1/ITS4 (Imran et al. 2022). The sequence was submitted into GenBank database (ON878059). BLAST analysis of the LH7's ITS amplicon showed 100% similarity with that of JN093303.1. A phylogenetic tree constructed using the maximum likelihood method revealed that ON878059 was clustered with JN093303.1. Previous studies have documented that pathogens such as Colletotrichum gloeosporioides (Penz.), Fusarium spp. and Rhizopus oryzae can also cause diseases in A. vera in China (Zhou et al. 2008; Ding et al. 2015). Additinonally, Cladosporium sphaerospermum, Pseudopestalotiopsis theae, and Lasiodiplodia theobromae have been identified as causal agents of aloe leaf spot diseases in India, Bangladesh and Malaysia (Avasthi et al. 2016; Ahmmed et al. 2022; Khoo et al. 2022). To our knowledge, this is the first report of N. dimidiatum causing leaf necrosis of aloe in China. Vigilant surveillance and disease control measures are imperative to mitigate potential losses in this region.

Complete genome sequence of a novel closterovirus isolated from Dregea volubilis.

The complete genome sequence of a putative novel closterovirus, tentatively named "Dregea volubilis closterovirus 1" (DvCV1, GenBank accession no. MZ779122), infecting Dregea volubilis in China was determined using high-throughput sequencing (HTS). The complete genome sequence of DvCV1 consists of 16,165 nucleotides (nt) and contains nine ORFs. The genome structure of DvCV1 is typical of members of the genus Closterovirus. Complete genome sequence analysis showed that DvCV1 shares 41.4-48.4% nucleotide sequence identity with other known closteroviruses. The putative RNA-dependent RNA polymerase (RdRp), heat shock protein 70-like protein (HSP70h), and coat protein (CP) of DvCV1 share 46.80-62.65%, 31.06-51.80%, and 28.34-37.37% amino acid sequence identity, respectively, with the RdRp, HSP70h and CP of other closteroviruses. Phylogenetic analysis based on HSP70h aa sequences placed DvCV1 alongside other members of the genus Closterovirus in the family Closteroviridae. These results suggest that DvCV1 is a new member of the genus Closterovirus. This is the first report of a closterovirus infecting D. volubilis.

Complete genome sequence of a novel mitovirus detected in Paris polyphylla var. yunnanensis.

Paris mitovirus 1 (ParMV1) is a positive-sense RNA virus that was detected in diseased Paris polyphylla var. yunnanensis plants in Wenshan, Yunnan. The complete genome sequence of ParMV1 is 2,751 nucleotides in length, and the genome structure is typical of mitoviruses. The ParMV1 genome has a single open reading frame (ORF; nt 358-2,637) that encodes an RNA-dependent RNA polymerase (RdRp) with a predicted molecular mass of 86.42 kDa. ParMV1 contains six conserved motifs (Ι-VΙ) that are unique to mitoviruses. The 5' and 3' termini of the genome are predicted to have a stable secondary structure, with the reverse complementary sequence forming a panhandle structure. Comparative genome analysis revealed that the RdRp of ParMV1 shares 23.1-40.6% amino acid (aa) and 32.3-45.7% nucleotide (nt) sequence identity with those of other mitoviruses. Phylogenetic analysis based on RdRp aa sequences showed that ParMV1 clusters with mitoviruses and hence should be considered a new member of the genus Mitovirus in the family Mitoviridae. This is the first report of a novel mitovirus infecting Paris polyphylla var. yunnanensis.