Molecular, Phenotypical, and Host-Range Characterization of Robbsia andropogonis Strains Isolated from Bougainvillea spp. in Mexico

Unlocking a Mystery: Characterizing the First Appearance of Clavibacter nebraskensis in Mexican Cornfields

The Goss's wilt and leaf blight is a disease of maize (Zea mays) caused by Clavibacter nebraskensis, which was widespread in the last several years throughout the Midwest in the United States, south in Texas, and north to Canada. The bacterium is included within the high-risk list of quarantine pathogens by many plant protection organizations and countries including Mexico. Severe blight symptoms on maize plants were found in different provinces from Coahuila and Tlaxcala, Mexico, in 2012 and 2021, respectively. Twenty bacterial isolates with morphology similar to C. nebraskensis were obtained from the diseased maize leaves. The isolates were confirmed by phenotypic tests and 16S rRNA and gyrB sequencing. Two strains were tested for pathogenicity tests on seven hybrid sweet corn cultivars available in Mexico, and the most sensitive cultivar was tested for all the strains to fulfill Koch's postulates. The phylogenetic reconstruction based on two single loci reveals a remarkable clustering of Mexican strains to American strains reported approximately 50 years ago. The presence of this pathogen represents a risk and a significant challenge for plant protection strategies in Mexico and maize diversity.

Robbsia betulipollinis sp. nov., Isolated from Pollen of Birch (Betula pendula)

One gram-negative strain designated Bb-Pol-6 ^T was isolated from birch (Betula pendula) pollen at Giessen area, Germany. The analysis of 16S rRNA gene-based phylogenies indicated the next-relative genera were Robbsia, Chitinasiproducens, Pararobbsia and Paraburkholderia (96-95.6%). Further comparative genome analysis and phylogenetic tree-based methods revealed its phylogenetic position under the genus Robbsia. The genome of strain Bb-Pol-6 ^T was 5.04 Mbp with 4401 predicted coding sequences and a G + C content of 65.31 mol%. Average amino acid identity, average nucleotide identity, digital DNA-DNA hybridization and percentage of conserved proteins values to Robbsia andropogonis DSM 9511 ^T were 68.0, 72.5, 22.7 and 65.85%, respectively. Strain Bb-Pol-6 ^T was rod-shaped, non-motile, facultative anaerobic and grew optimally at 28 °C and pH 6-7. Ubiquinone 8 was the major respiratory quinone and the major cellular fatty acids were C_16:0, C_{19:0 cyclo} ω7c, C_{17:0 cyclo} ω7c and C_17:1 ω6c. The dominant polar lipids were diphosphatidylglycerol, phosphatidylethanolamine, phosphatidylglycerol and an unidentified aminophospholipid. Based on the genomic physiological and phenotypic characteristics, strain Bb-Pol-6 ^T was considered a novel species under the genus Robbsia, for which the name Robbsia betulipollinis sp. nov. was proposed. The type strain is Bb-Pol-6 ^T (= LMG 32774 ^T = DSM 114812 ^T).

Draft Genome Sequences of Robbsia andropogonis Isolated from Sorghum bicolor Exhibiting Bacterial Leaf Stripe in Australia

Robbsia andropogonis causes leaf spots, streaks, or stripes on a wide range of commercially important crops. Here, we present the draft genome sequences of two isolates of R. andropogonis sourced from Sorghum bicolor displaying symptoms of bacterial leaf stripe disease in Australia.