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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. [ABSTRACT FROM AUTHOR]

Sugarcane brown rust, caused by Puccinia melanocephala, is a severe foliar disease that occurs in almost all countries where sugarcane is grown. The main control strategy is the use of resistant cultivars. The aim of this work was to identify molecular markers linked to genomic regions associated with a novel brown rust resistance source in sugarcane. An F1 progeny of 300 clones was obtained from a cross between TUC 00–36 and RA 87–3, highly susceptible and highly resistant to brown rust, respectively. A total of 60 F1 clones with extreme phenotype, either highly susceptible or highly resistant to brown rust, were selected. This "pooled tail" population was tested for reactions to brown rust under natural infection in the field during two crop seasons and under artificial infection in the greenhouse. Whole‐genome profiling was performed by DArT‐seq technology. Phenotypic data under both conditions and 23,299 single‐nucleotide polymorphisms (SNPs) obtained from genotyping were analysed to identify markers linked to the resistance trait. Single mapping analyses and subsequent multiple regression showed that 34 SNP markers were significantly linked to resistance alleles. These SNPs jointly explained 69% and 66% of the total phenotypic variation (R2) observed for field and controlled conditions, respectively. The mapping of the 34 SNP sequences revealed that 19 markers aligned to the sugarcane genome, whereas 12 markers aligned to the sorghum genome, all grouped on chromosome 5 with some functional annotations related to vegetal defence response. These marker loci could contribute to the development of molecular tools for molecular marker‐assisted breeding. [ABSTRACT FROM AUTHOR]

A significant increase in the occurrence of red stripe (caused by Acidovorax avenae subsp. avenae) has been observed in the last decade in Argentina. Considering that no extensive sampling of the main sugarcane‐producing area in the country has been conducted to characterize the diversity and population structure of A. avenae subsp. avenae, molecular markers were employed to analyse 112 isolates from Tucumán. By using repetitive element polymorphism‐based polymerase chain reaction (rep‐PCR) almost all isolates were differentiated and grouped into 10 clusters, revealing a high genetic diversity. Using the amplified fragment length polymorphism (AFLP) technique, five pairs of isolates were discriminated that could not be distinguished with rep‐PCR. Cluster analysis showed no clear association between isolate clustering, sugarcane host genotype, crop age, type of tissue sampled, fertilization, or year of sampling. Linkage equilibrium analysis by using rep‐PCR data indicated that the population has some degree of clonality. Three housekeeping genes were also sequenced: ugpB and pilT sequences were highly similar to A. avenae subsp. avenae sequences from other Argentinian isolates, whereas the lepA sequence did not reveal significant similarity. An additional four housekeeping genes could not be amplified, suggesting the existence of differences in those regions. Subsequently, virulence of 14 A. avenae subsp. avenae isolates was evaluated under controlled conditions. Results showed a differential level of aggressiveness among the isolates on a resistant sugarcane variety. This study confirmed that rep‐PCR is an adequate tool for genetic analysis and population structure characterization in bacteria, and revealed both high genetic diversity and clonal population structure of A. avenae subsp. avenae in Tucumán, Argentina. [ABSTRACT FROM AUTHOR]