Genetic variability of Pseudocercospora fijiensis, the black Sigatoka pathogen of banana (Musa spp.) in Mexico

摘要

Pseudocercospora (previously known as Mycosphaerella) fijiensis causes black Sigatoka disease in banana (Musa spp.) and is considered to be the most devastating pathogen of this crop worldwide. To improve knowledge of its evolutionary patterns, this study determined the genetic variability of populations from two regions of Mexico: Central Pacific (Colima and Michoacan) and Southern (Chiapas, Tabasco and Oaxaca), using 10 simple sequence repeat (SSR) loci and the MAT-specific PCR assay. Both mating types were present in all regions under study, with frequencies of 63% MAT1-1 and 37% MAT1-2. The SSR markers showed an average of three alleles per locus, resulting in 34 alleles in total. The genetic diversity (H-T) was 0.3308, but at the local level (H-S) ranged from 0.0976 (Colima) to 0.2228 (Oaxaca). However, the genotypic diversity was usually high (H ' > 2.4, S > 0.89). Cluster analysis grouped the isolates into five clusters with high statistical support (au > 80%), suggesting a geographic organization of the genetic variability of P. fijiensis; AMOVA, the minimum spanning tree and the population structure analysis supported this result, and all data indicated that the major genetic differences were between the different populations under analysis. Thus, the high level of genetic variability in P. fijiensis is attributed partly to a high rate of sexual reproduction, and also to a strong evolutionary capacity coupled with isolation due to limited genetic flow between distant populations. Both possibilities could be playing a relevant role in population differentiation of the pathogen.