Molecular characterization of a novel ambiguivirus isolated from the phytopathogenic fungus Setosphaeria turcica.

In this study, a novel single-stranded RNA virus was isolated from the plant-pathogenic fungus Setosphaeria turcica strain TG2, and the virus was named "Setosphaeria turcica ambiguivirus 2" (StAV2). The complete nucleotide sequence of the StAV2 genome was determined using RT-PCR and RLM-RACE. The StAV2 genome comprises 3,000 nucleotides with a G+C content of 57.77%. StAV2 contains two in-frame open reading frames (ORFs) with the potential to produce an ORF1-ORF2 fusion protein via a stop codon readthrough mechanism. ORF1 encodes a hypothetical protein (HP) of unknown function. The ORF2-encoded protein shows a high degree of sequence similarity to the RNA-dependent RNA polymerases (RdRps) of ambiguiviruses. BLASTp searches showed that the StAV2 HP and RdRp share the highest amino acid sequence identity (46.38% and 69.23%, respectively) with the corresponding proteins of a virus identified as "Riboviria sp." isolated from a soil sample. Multiple sequence alignments and phylogenetic analysis based on the amino acid sequences of the RdRp revealed that StAV2 is a new member of the proposed family "Ambiguiviridae".

Kosakonia cowanii, a new bacterial pathogen affecting foxtail millet (Setaria italica[L.]P. Beauv.) in China.

Foxtail millet (Setaria italica [L.] P. Beauv.) is an important cereal worldwide. From 2021 to 2022, stalk rot disease of foxtail millet was identified in Shanxi province, northern China, with an 8% and 2% field incidence rate in Xinzhou (2 different locations), respectively. It caused necrosis, decay, stem lodging, and sometimes death. This study aimed to identify the causal agent of the disease through morphophysiological and molecular identification of the isolates. Stalk rot specimens were collected in Xinzhou, from foxtail millet plants exhibiting typical symptoms, and the pathogen was isolated with dilution plating. It was cultured at 28 °C for 48 h on nutrient agar, revealing circular, convex, and pale-yellow colonies, with a smooth surface and an entire edge. Scanning electron microscopy showed that the pathogen is rod shaped, round ended and has an uneven surface ranging from 0.5 to 0.7 µm in diameter and 1.2-2.7 µm in length. It is a motile gram-negative facultative anaerobic bacterium that can reduce nitrate and synthesize catalase but cannot hydrolyze starch. It also shows a negative reaction in the methyl red test and optimum growth at 37 °C. The pathogenicity test was performed on foxtail millet variety 'Jingu 21' stem to confirm Koch's postulates. The biochemical tests were done in the Biolog Gen III MicroPlate, revealing 21 positive chemical sensitivity tests, except those for minocycline and sodium bromate. Furthermore, among 71 carbon sources, the pathogen utilized 50 as the sole carbon source, including sucrose, d-maltose, α-d-lactose, d-galactose, D-sorbitol, D-mannitol, glycerol, and inositol. Finally, molecular characterization of the pathogen using 16S rRNA and rpoB gene sequencing and subsequent phylogenetic analysis identified the strain as Kosakonia cowanii. This study is the first to report K. cowanii as a stalk rot-causing pathogen in foxtail millet.

[Genetic diversity of 21 Fusarium strains in Section Martiella based on ISSR analysis].

In order to understand the genetic difference and phylogenic relationship within and among the Fusarium species in Section Martiella, the genetic diversity of 21 Fusarium strains in the section was examined by inter-simple sequence repeats (ISSR). Fifteen selected ISSR primers were adopted to do amplification, and a total of 239 bands were amplified, among which, 230 (96.2%) were polymorphic, with an average of 15.3 polymorphic bands per primer. The genetic similarity ranged from 0.494 to 0.933, with an average of 0.640. All the test strains were clustered into two groups at genetic similarity of 0.593. The strains 1-17 were grouped into IG-I, belonging to Fusarium solani and F. solani var. coeruleum, while the strains 18-21 were grouped into IG-II, belonging to F. ventricosum. All the 21 strains could be entirely distinguished at genetic similarity of 0. 933. The SSR loci in the Fusarium genomes were rich in polymorphism. The ISSR grouping had definite correlation with the species classification, but less correlation with the geographic origin of the strains. Within the same ISSR groups, there existed definite correlation between the genetic similarity and the geographic origin of the strains. Within the same species collected from the same regions and same host plants, there existed definite genetic difference among the strains of the same species.