ABSTRACT
Sporisorium scitamineum is the fungus that causes sugarcane smut disease. Despite of the importance of sugarcane for Brazilian agribusiness and the persistence of the pathogen in most cropping areas, genetic variation studies are still missing for Brazilian isolates. In this study, sets of isolates were analyzed using two molecular markers (AFLP and telRFLP) and ITS sequencing. Twenty-two whips were collected from symptomatic plants in cultivated sugarcane fields of Brazil. A total of 41 haploid strains of compatible mating types were selected from individual teliospores and used for molecular genetic analyses. telRFLP and ITS analyses were expanded to six Argentine isolates, where the sugarcane smut was first recorded in America. Genetic relationship among strains suggests the human-mediated dispersal of S. scitamineum within the Brazilian territory and between the two neighboring countries. Two genetically distinct groups were defined by the combined analysis of AFLP and telRFLP. The opposite mating-type strains derived from single teliospores were clustered together into these main groups, but had not always identical haplotypes. telRFLP markers analyzed over two generations of selfing and controlled outcrossing confirmed the potential for emergence of new variants and occurrence of recombination, which are relevant events for evolution of virulence and environmental adaptation.
Subject(s)
Genetic Variation , Genotype , Plant Diseases/microbiology , Saccharum/microbiology , Ustilaginales/classification , Ustilaginales/genetics , Amplified Fragment Length Polymorphism Analysis , Brazil , Cluster Analysis , DNA, Fungal/chemistry , DNA, Fungal/genetics , DNA, Ribosomal Spacer/chemistry , DNA, Ribosomal Spacer/genetics , Genes, Mating Type, Fungal , Molecular Typing , Mycological Typing Techniques , Phylogeny , Polymorphism, Restriction Fragment Length , Sequence Analysis, DNA , Ustilaginales/isolation & purificationABSTRACT
Leaf scald is one of the most important diseases of sugarcane in Brazil. Despite its importance, little is known about the genetic and pathogenic variability of its causal agent, Xanthomonas albilineans. The genetic diversity of 44 X. albilineans isolates from diverse geographic regions of Brazil was assessed using 15 newly developed short sequence repeat (SSR) loci designed from the genome sequence of X. albilineans strain GPE PC73. In addition, the aggressiveness of each isolate was evaluated by inoculating on a susceptible sugarcane cultivar and scoring the disease severity. Of the 15 SSR loci, 12 were polymorphic and produced 54 polymorphic alleles. The average number of polymorphic alleles per locus was 4.5, and ranged from 2 to 12 alleles. Phenetic analysis based on Nei's unbiased genetic distance, clustered the isolates into two major groups. Group I included 32 isolates from all four geographic regions studied, whereas group II included 9 isolates from two regions. Three isolates did not cluster within these groups. Analysis of disease severity data also revealed variability in aggressiveness among isolates but no correlation could be established with either SSR haplotypes or phenetic groups. Isolates with identical haplotypes differed in aggressiveness and vice versa. However, single marker-trait analysis revealed two markers associated with this trait.
