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.

Control of Fusarium verticillioides on corn with a combination of Bacillus subtilis TM3 formulation and botanical pesticides

The aim of this study was to evaluate the effectiveness of the combination of Bacillus subtilis TM3 formulation with botanical pesticides in suppressing Fusarium verticilloides infection in corn. The research was carried out at the Plant Pathology Laboratory and the Experimental Farm of Indonesian Cereals Research Institute (ICERI) from February to November 2019. The research consisted of two stages, namely an in vitro test of antagonists of botanical pesticides against F. verticilloides using 5 types of plant extracts namely betel leaf extract, turmeric, galangal, cosmos, and clove leaf. The second stage was to test the effectiveness of the combination of the formulation of B. subtilis TM3 with the best 3 types of plant extracts in vitro testing in suppressing F. verticilloides infection in plants. The results of the in vitro study showed that the plant extracts of betel leaf, clove leaf and galangal had the best inhibitory ability on the mycelia growth of F. verticilloides. Meanwhile, the field test found that the application of the B. subtilis TM3 formulation, either alone or in combination with plant extracts, was able to suppress F. verticilloides infection. The combination of B. subtilis TM3 formulation with betel leaf extract showed the best inhibition of 20% against stem rot disease and 13.33% against corn cob rot. This treatment did not affect production quantitatively, but was able to suppress the decline in seed quality due to F. verticilloides infection. Seeds grown by the Plastic Rolled Paper Test (PRPT) method were not only infected with F. verticilloides, but also infected with other seed-borne pathogens, such as Aspergillus niger and A. falvus. The presence of these two pathogens did not inhibit the growth of F. verticilloides in kernels.

FvSO regulates vegetative hyphal fusion, asexual growth, fumonisin B1 production, and virulence in Fusarium verticillioides

Hyphal anastomosis is a hallmark of filamentous fungi and plays vital roles including cellular homoeostasis, interhyphal communication and nutrient translocation. Here we identify a gene, FvSO, in Fusarium verticillioides, a filamentous ascomycete causing maize ear and stalk rot and producing fumonisin mycotoxins. FvSO, like its Neurospora crassa homologue SO, is required for vegetative hyphal fusion. It is also essential for normal vegetative growth, sporulation, and pathogenesis. FvSO encodes a predicted WW domain protein and shares 70 % protein sequence identity with N. crassa SO. FvSO deletion mutants (ΔFvSO) had abnormal distribution of conidia size, and conidia of ΔFvSO germinated much later and slower than wild type. ΔFvSO was deficient in hyphal anastomosis, had slower radial growth and produced less fungal biomass than wild type. ΔFvSO were unable to perform anastomosis, a key feature of filamentous fungi. Interestingly, production of fumonisin B1 by ΔFvSO was significantly reduced compared to wild type. Additionally, ΔFvSO was nonpathogenic to corn ears, stalks and seedlings, likely due to defective growth and development. In conclusion, FvSO is essential for vegetative hyphal fusion and is required for normal vegetative growth and sporulation, normal levels of fumonisin production and pathogenicity in F. verticillioides. The pleiotropic nature of ΔFvSO phenotypes suggests that FvSO is likely involved in certain signalling pathways that regulate multiple cellular functions.