SnToxA, SnTox1, and SnTox3 originated in Parastagonospora nodorum in the Fertile Crescent

Fariba Ghaderi,Bruce A Mcdonald,Bahram Sharifnabi,Patrick C Brunner,Mohammad Javan‐Nikkhah

doi:10.1111/ppa.13233

Fariba Ghaderi, Bruce A Mcdonald + Show 3 more

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https://doi.org/10.1111/ppa.13233

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Abstract

AbstractThe centre of origin of the globally distributed wheat pathogen Parastagonospora nodorum has remained uncertain because only a small number of isolates from the Fertile Crescent were included in earlier population genetic and phylogeographic studies. We isolated and genetically analysed 193 P. nodorum strains from three naturally infected wheat fields distributed across Iran using 11 neutral microsatellite loci. Compared to previous studies that included populations from North America, Europe, Africa, Australia, and China, the populations from Iran had the highest genetic diversity globally and also exhibited greater population structure over smaller spatial scales, patterns typically associated with the centre of origin of a species. Genes encoding the necrotrophic effectors SnToxA, SnTox1, and SnTox3 were found at a high frequency in the Iranian population. By sequencing 96 randomly chosen Iranian strains, we detected new alleles for all three effector genes. Analysis of allele diversity showed that all three effector genes had higher diversity in Iran than in any population included in previous studies, with Iran acting as a hub for the effector diversity that was found in other global populations. Taken together, these findings support the hypothesis that P. nodorum originated either within or nearby the Fertile Crescent with a genome that already encoded all three necrotrophic effectors during its emergence as a pathogen on wheat. Our findings also suggest that P. nodorum was the original source of the ToxA genes discovered in the wheat pathogens Phaeosphaeria avenaria f. sp. tritici 1, Pyrenophora tritici‐repentis, and Bipolaris sorokiniana.

Highlights

IntroductionPhaeosphaeria nodorum) is the causal agent of Stagonospora nodorum leaf and glume blotch (SNB) on durum and bread wheat (Quaedvlieg et al 2013)
The combined Iranian population came from four provinces, separated by mountains and deserts, that are characterized by different climates, cropping systems, wheat cultivars and growing seasons, with distances among Iranian field populations ranging from 250-800 km
Measures of genetic diversity in the combined Iranian populations of P. nodorum were compared with identical measures made in an earlier analysis that included 693 P. nodorum isolates sampled from 17 wheat fields coming from nine regions distributed across five continents, with none of these earlier collections coming from the Fertile Crescent (Stukenbrock et al 2006)

Summary

Introduction

Phaeosphaeria nodorum) is the causal agent of Stagonospora nodorum leaf and glume blotch (SNB) on durum and bread wheat (Quaedvlieg et al 2013). This disease is found in most wheat-growing regions of the world (Wiese, 1987) and can cause yield losses of up to 31% (Bhathal et al 2003). The genetic structure of P. nodorum populations has been analyzed at field, regional, continental, and global scales using several types of neutral genetic markers, including restriction fragment length polymorphisms (RFLPs) (McDonald et al 1994; Keller et al 1997a, 1997b), amplified fragment length polymorphisms (AFLPs) (Bennett et al 2005) and microsatellites ( called simple sequence repeats or SSRs) (Stukenbrock et al 2005).

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