Genética molecular de populações de Alternaria solani no Brasil / Molecular population genetics of Alternaria solani in Brazil

AUTOR(ES)
DATA DE PUBLICAÇÃO

2008

RESUMO

The analysis of the genetic structure of the population of Alternaria solani is an important component of the molecular epidemiology potato (Po) and tomato (To) early blight. Isolates were sampled from the Northeast, Central-West, Southeast, and South regions of Brazil. AFLP and RAPD markers were used to estimate genetic diversity. A multilocus combined dataset using AFLP and RAPD matrices generated 123 AS haplotypes with 62 loci (92% polymorphism). The allele frequency for AS populations from To and Po ranged from 0.015 (RAPD45) to 1.000 (RAPD47, RAPD56, RAPD57, RAPD59, RAPD61, RAPD62). The theta estimate (Ө) and the Gst average values were 0.29 (P= 0.001), and 0.18, respectively. However, there was greater genetic variation within (70.6%) than between (29.4%) AS populations. There was evidence of AS haplotypes associated with Po. High gene diversity was detected over all AS population (h=0.36, S.D. 0.38). The genotypic diversity measured by both Shannon-Wiener (H ) and Stoddart &Taylor s G for Po and To populations were 1.01 and 1.00, and 0.99 and 0.98, respectively. There was no evidence of recombination (IA = 7.24728, P<0.001). In addition, gene genealogies based on the coalescent process were used to infer about evolutionary mechanisms. Sequences of the Alt a 1 and glyceraldehyde-3-phosphate dehydrogenase (Gpd) genes, and rDNA internal transcribed spacer region (ITS) were used to assess molecular diversity and for the coalescent analyses. Sequences from 111, 110, and 104 isolates were obtained for the Alt a 1 (471 bp) and Gpd (584 bp) genes, and for the ITS region (578 bp), respectively. The highest number of parsimony informative sites (14), nucleotide diversity (0.007) and the average number of nucleotide differences (3.202) were obtained for Alt a 1. Although the highest number of haplotypes (7) was generated for ITS, haplotype diversity was the lowest (0.15) for this region. The genetic differentiation between AS populations was detected for Alt a 1 sequences. Recombination was not detected, however, subdivision and recent divergence time were inferred from populations associated with hosts. There is no evidence of geographic subdivision, and gene flow is occurring among AS populations. Phylogenetic analyses were conducted using Alt a 1, Gpd, and ITS sequences. In addition, RAPD marker was combined with Alt a 1 and Gpd sequences for parsimony analysis. Association of AS with Po and To was detected when analyzing Alt a 1 and Gpd loci with significant bootstrap (>70) and Bayesian Posterior Probability (>95) values. Despite significant incongruence for the combined dataset (P=0.01), positive values of Partitioned Bremer Support were obtained for a node which clustered AS lineages associated with potato and tomato plants. Thus, there was evidence of pathogen clonal lineages associated with hosts. Gene flow and mutation are the main evolutionary mechanisms affecting AS population.

ASSUNTO(S)

fungos fitopatogênicos genética molecular fitopatologia plant pathogenic fungi molecular genetics alternaria solani alternaria solani

ACESSO AO ARTIGO

Documentos Relacionados