Multiple gene genealogy reveals high genetic diversity and evidence for multiple origins of Chinese Plasmopara viticola population

Wei Zhang,Xueyan Zhao,Xinghong Li,Jianping Xu,Kevin D Hyde,Jiye Yan,Jianhua Liu,K W Thilini Chethana,Wensheng Zhao,Ishara S Manawasinghe,Siraprapa Brooks

doi:10.1038/s41598-017-17569-7

Abstract

Downy mildew caused by Plasmopara viticola is one of the most devastating diseases of grapevines worldwide. So far, the genetic diversity and origin of the Chinese P. viticola population are unclear. In the present study, 103 P. viticola isolates were sequenced at four gene regions: internal transcribed spacer one (ITS), large subunit of ribosomal RNA (LSU), actin gene (ACT) and beta-tubulin (TUB). The sequences were analyzed to obtain polymorphism and diversity information of the Chinese population as well as to infer the relationships between Chinese and American isolates. High genetic diversity was observed for the Chinese population, with evidence of sub-structuring based on climate. Phylogenetic analysis and haplotype networks showed evidence of close relationships between some American and Chinese isolates, consistent with recent introduction from America to China via planting materials. However, there is also evidence for endemic Chinese P. viticola isolates. Our results suggest that the current Chinese Plasmopara viticola population is an admixture of endemic and introduced isolates.

Highlights

Grape downy mildew caused by Plasmopara viticola (Berk & Curt.) Berl. &
We observed grapevine leaves with oil spot symptoms, necrotic lesions and characteristic sporulation of the pathogen from the underside of the leaf (Fig. 2)
The most common symptoms observed in the field were characteristic sporulation on the rachis and infections on young berries (Fig. 2)

Summary

Introduction

Grape downy mildew caused by Plasmopara viticola (Berk & Curt.) Berl. &. In China, grapevine downy mildew was first reported in 18997 At present, this disease can be observed in almost all Chinese grape vineyards, causing significant yield losses. Many studies have been conducted to understand disease epidemiology and resistance development against P. lasmopara viticola in China It is less known about the population structure of this pathogen. Previous studies have shown that the causal agent of grape downy mildew, P. viticola, exhibits four cryptic lineages, which are structured according to the host species; Vitis aestivlis, V. labrusca, V. riparia and V. vinifera[4]. Several studies have been conducted to elucidate the genetic diversity and population structure of grape downy mildew pathogens using various molecular markers[4,7,14,15,16,17]. We hypothesized that if P. viticola was introduced to China via planting materials, there might be a close phylogenetic relationship between Chinese isolates and American isolates

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