Genetic Structure of the Population of Alternaria solani in Brazil

摘要

Understanding the genetic structure of the populationof Alternaria solani (AS) is an important component ofepidemiological studies of early blight, a severe diseasethat affects potato (Po) and tomato (To) worldwide.Up to 150 isolates obtained from both hosts wereanalysed with RAPD and AFLP markers to estimatethe amount and distribution of genetic variability ofAS in Brazil. Using RAPD, gene diversity (h = 0.20)and scaled indices of diversity of Shannon (H = 0.66)and Stoddart and Taylor's (G = 0.31) for the Po populationwere higher than those of the To (h = 0.07,H = 0.34, G = 0.17). For AFLP, the statistics forthe Po (h = 0.17, H = 0.86, G = 0.49) and To (h =0.17, H = 0.85, G = 0.36) populations were similar.For each RAPD and AFLP locus, the allele frequencyfor the overall population ranged from 0.006 to 0.988,and 0.007 to 0.993, respectively. Genetic differentiationwas high (GST = 0.41 and h = 0.59) and moderatelyhigh (GST = 0.23 and h = 0.37) when estimated withRAPD and AFLP, respectively. Based on cluster analyses,there was strong evidence of association of pathogenhaplotypes with host species. The null hypothesis ofrandom association of alleles was rejected in the analysisof both RAPD (IA = 13.1, P < 0.001) and AFLP(IA = 2.2, P < 0.001) markers. The average number ofmigrants was estimated to be around one and two individualsper generation, using RAPD and AFLP, respectively.There was no correlation between geneticdistance and geographical origin of AS haplotypes forRAPD (r = )0.07, P = 0.84) and AFLP (r = )0.03,P = 0.70). The AS population is clonal with highgenetic variability, and there is genetic differentiationbetween the populations that affect To and Po.