Historical and contemporary multilocus population structure of Ascochyta rabiei (teleomorph: Didymella rabiei) in the Pacific Northwest of the United States

Abstract

The historical and contemporary population genetic structure of the chickpea Ascochyta blight pathogen, Ascochyta rabiei (teleomorph: Didymella rabiei), was determined in the US Pacific Northwest (PNW) using 17 putative AFLP loci, four genetically characterized, sequence-tagged microsatellite loci (STMS) and the mating type locus (MAT). A single multilocus genotype of A. rabiei (MAT1-1) was detected in 1983, which represented the first recorded appearance of Ascochyta blight of chickpea in the PNW. During the following year many additional alleles, including the other mating type allele (MAT1-2), were detected. By 1987, all alleles currently found in the PNW had been introduced. Highly significant genetic differentiation was detected among contemporary subpopulations from different hosts and geographical locations indicating restricted gene flow and/or genetic drift occurring within and among subpopulations and possible selection by host cultivar. Two distinct populations were inferred with high posterior probability which correlated to host of origin and date of sample using Bayesian model-based population structure analyses of multilocus genotypes. Allele frequencies, genotype distributions and population assignment probabilities were significantly different between the historical and contemporary samples of isolates and between isolates sampled from a resistance screening nursery and those sampled from commercial chickpea fields. A random mating model could not be rejected in any subpopulation, indicating the importance of the sexual stage of the fungus both as a source of primary inoculum for Ascochyta blight epidemics and potentially adaptive genotypic diversity.

Genetic diversity and population structure of Ascochyta rabiei from the western Iranian Ilam and Kermanshah provinces using MAT and SSR markers

“…The main evolutionary forces that contribute to the genetic structure within and between populations are gene flow, genetic drift, reproduction/mating systems, population size, and selection. Molecular markers have been widely deployed to detect and identify A. rabiei isolates and to examine genetic diversity, genetic structure, and virulence in populations of this fungus (Morjane et al 1994;Peever et al 2004;Phan et al 2003;Santra et al 2001;Udupa et al 1998). Significant genetic variation was shown in populations of A. rabiei in Italy (Fischer et al 1995), Tunisia Morjane et al 1994), Syria and Lebanon (Udupa et al 1998), Spain (NavasCortés et al 1998), Pakistan (Jamil et al 2000) and India (Santra et al 2001).…”

Ecological Genetic Divergence of the Fungal PathogenDidymella rabieion Sympatric Wild and DomesticatedCicerspp. (Chickpea)

“…Isolates were screened for allelic variation at six sequence-tagged microsatellite (STMS) loci (30), which have been demonstrated to be genetically unlinked (50,52; T. L. Peever, unpublished data). PCR amplifications were performed as described by Peever et al (50) with minor modifications.…”

An Update on Genetic Resistance of Chickpea to Ascochyta Blight

“…Sexual reproduction is controlled by a single regulatory locus referred to as a mating-type locus and alternate sequences at the mating-type locus are completely dissimilar and code for different regulatory genes. The presence of opposite mating types (MAT1-1 and MAT1-2) and the teleomorph have been reported from some chickpea-growing regions in the world [24][25][26][27][28][29]. The morphological characteristics of A. rabiei and Phoma medicaginis var.…”