Xanthomonas albilineans and Xanthomonas sacchari isolated from sugarcane with leaf scald disease symptoms: friends or foes?

FLORENCIA D NAVARRO ; EVA M FIGUEROLA ; ROMINA P BERTANI; CONSTANZA M JOYA; ADRIÁN A VOJNOV; NATALIA MIELNICHUK

Salta y Jujuy

Workshop; XII Pathology and XI Entomology Workshop: Dealing with sugar cane pests and diseases in the context of regenerative agriculture.; 2024

ISSCT - SATCA

Our group characterized three Xanthomonas albilineans strains (Xa32, Xa33 and XaM6) and two Xanthomonas sacchari stains (Xs14 and Xs15) isolated from sugarcane (Saccharum spp.) with leaf scald symptoms in Tucumán, Argentina. Although Xs showed virulence factors production, its pathogenicity and/or contribution to disease caused by Xa are unknown. This study aimed to characterize Xa and Xs genotypically and phenotypically to determine interactions that could promote leaf scald. Xa32 and Xs14 strains were selected for this work. Genomes were sequenced (Illumina HiSeq), assembled (SPAdes) and annotated using RAST/PROKKA. Pathogen-Host Interaction database (PHI) and Virulence Factor Database (VFDB) predicted genes involved in host and microorganisms interaction. Average Nucleotide Identity (ANI) and phylogenetic trees were constructed using Type (Strain) Genome Server (dsmz). For phenotypic characterization, infection conditions for each strain were set up using a susceptible variety. Dual culture assays, co-cultivation experiments and confocal laser microscopy analysis to observe Xa32 planktonic-sessile transition in the presence of Xs14-exopolysaccharide were carried out to determine bacterial interaction in vitro. Draft genome size was 3,840,059 bp for Xa32 and 5,048,087 bp for Xs14, with 3976 and 4547 predicted coding sequences, respectively, and no extrachromosomal plasmids detected. ANI values confirmed Xa32 identity (above 98.2%) but were inconclusive for Xs14 (above 93.4%). Unique PHI and VFDB hits were found for both strains. Xa32 produced pencil-line symptoms and colonized plant tissue, unlike Xs14. Neither Xa32 nor Xs14 showed growth inhibition halos when confronted (bacteria vs. bacteria or bacteria vs. cell-free-supernatant); however, Xs14 inhibited Xa32 growth when both bacteria were in contact on solid media and co-cultivated in liquid media. Besides, Xa32 adhered and developed sessile-structures upon Xs14-exopolysaccharide incubation. In conclusion, genome analysis revealed differences between both species; Xa32 was confirmed as a sugarcane pathogen while Xs14 as non-pathogenic. Bacterial interaction suggested competition mechanisms, though cooperative interactions in biofilm-like communities may also exist.