Comparative study of virulence factors, pathogenicity and genetic diversity of Acidovorax avenae subsp. avenae, the causal agent of red stripe disease in sugarcane

Abstract

Acidovorax avenae subsp. avenae (Aaa) is the causal agent of red stripe in sugarcane, a disease characterized by two forms: leaf stripe and top rot. Despite the importance of this disease, little is known about Aaa infection mechanisms, and studies of virulence factors (VFs) have not been reported. Previous analysis of Aaa isolates obtained from sugarcane fields in Tucumán, Argentina, suggested that pathogenicity was not related to genetic groups determined by rep-PCR analysis. Therefore, the aims of this work were to analyse VFs produced by Aaa strains from different genetic groups and to evaluate the association among VFs, between VFs and Aaa pathogenicity and between VFs and Aaa genetic diversity. Bacterial motility (sliding, swimming and twitching), extracellular enzyme activities (proteases, amylases and endoglucanases), H2O2-mediated oxidative stress, cell adhesion and exopolysaccharide (EPS) production were assayed in 14 Aaa isolates from different genetic groups. Pearson's correlation analysis and principal component analysis (PCA) were performed. For each VF analysed, values were variable presenting quantitative traits among the strains. Significant correlations were observed among the VFs, though no clear trend was identified between them and the pathogenicity or genetic group. Results reinforce the idea that a single VF does not account for the infection outcome, but a more complex process occurs where the interplay among VFs must be considered. The results of this study are crucial because they provide insight into the infection mechanism of this bacterium.