Genetic diversity and population structure of Emp

Authors: Khoshnood Nourollahi Mohammad Javannikkhah Mohammad Reza Naghavi Judith Lichtenzveig Sayed Mahmmod Okhovat Richard P Oliver Simon R Ellwood

Publish Date: 2010/04/10

Volume: 10, Issue: 1, Pages: 1-7

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Abstract

Knowledge of genetic diversity in A rabiei provides different levels of information that are important in the management of crop germplasm resources Gene flow on a regional level indicates a significant potential risk for the regional spread of novel alleles that might contribute to fungicide resistance or the breakdown of resistance genes Simple sequence repeat SSR and mating type MAT markers were used to determine the genetic structure and estimate genetic diversity and the prevalence of mating types in 103 Ascochyta rabiei isolates from seven counties in the Ilam and Kermanshah provinces of western Iran Ilam Aseman abad Holaylan Chardavol Dareh shahr Gilangharb and Sarpul A set of 3 microsatellite primer pairs revealed a total of 75 alleles the number of alleles varied from 15 to 34 for each marker A high level of genetic variability was observed among A rabiei isolates in the region Genetic diversity was high He = 0788 within populations with corresponding high average gene flow and low genetic distances between populations The smallest genetic distance was observed between isolates from Ilam and Chardavol Both mating types were present in all populations with the majority of the isolates belonging to Mat11 64 but within populations the proportions of each mating type were not significantly different from 50 Results from this study will be useful in breeding for Ascochyta blightresistant cultivars and developing necessary control measuresAscochyta blight caused by the fungus Ascochyta rabiei Pass Labr is the most destructive disease of aerial parts of chickpea Cicer arietinum L in chickpeaproducing regions of the world Nene and Reddy 1987 Iran is the fourth largest chickpea producer in the world http//faostatfaoorg of which Kermanshah and Ilam are important chickpea growing areas that suffer severe epidemics every year Ascochyta rabiei is a haploid heterothallic dothideomycete fungus within the class Pleosporales TraperoCasas and Kaiser 1992 Wilson and Kaiser 1995 The life cycle of this fungus involves several asexual generations during the growing season of the crop and a sexual or perfect stage Didymella rabiei Kovachevski v Arx which develops on infected plant debris during the winter NavasCortes et al 1998 TraperoCasas and Kaiser 1992 TraperoCasas et al 1996 Although the teleomorph’s influence on disease epidemiology and pathogen diversity is still unclear it may be more widespread than previously thought and ascospores may serve as a primary inoculum Kaiser and Hannan 1987 TraperoCasas et al 1996The disease appears in the field firstly as small infected foci and then spreads quickly when cool and wet conditions prevail The severity of disease can be reduced through the use of resistant cultivars fungicide applications and cultural practices such as crop rotation removal of debris and sowing clean seed Periodic appearances of new and more virulent strains of the pathogen are a major problem in resistance breeding Grewal 1984 Singh et al 1981The genetic structure of a population is the amount and distribution of genetic variation within and among populations of a species and reflects the evolutionary history of populations McDonald and Linde 2002 The amount of genetic variation within a population indicates how rapidly a pathogen can evolve and thus provides valuable information in predicting the effectiveness of control measures such as host resistance genes or chemical control McDermott and McDonald 1993 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 Geistlinger et al 2000 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 In some regions of the world where chickpea has only recently been introduced for example Australia and California only modest genetic diversity and a single mating type has been reported Kaiser 1997 Phan et al 2003To examine genetic diversity and population structure among 103 A rabiei isolates from western Iran we deployed simple sequence repeat SSR markers developed by Geistlinger et al 2000 Amongst different genetic markers available for such studies SSRs are routinely used because they are abundant distributed over the euchromatic part of the genome and are highly polymorphic Schlötterer and Ellegren 1998 Zane et al 2002 The presence distribution and frequency of A rabiei mating types in regions of Tunisia have been used to shed light on recent introductions as opposed to stable randomly mating populations Rhaiem et al 2007 To examine the relative proportions of MAT 11or MAT 12 allelic groups in this study we applied the MATspecific multiplex PCR assay developed by Barve et al 2003

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