High-Density Mapping and Candidate Gene Analysis of Pl18 and Pl20 in Sunflower by Whole-Genome Resequencing.

Guojia Ma,Qijian Song,Xuehui Li,Lili Qi

doi:10.3390/ijms21249571

Abstract

Downy mildew (DM) is one of the severe biotic threats to sunflower production worldwide. The inciting pathogen, Plasmopara halstedii, could overwinter in the field for years, creating a persistent threat to sunflower. The dominant genes Pl18 and Pl20 conferring resistance to known DM races have been previously mapped to 1.5 and 1.8 cM intervals on sunflower chromosomes 2 and 8, respectively. Utilizing a whole-genome resequencing strategy combined with reference sequence-based chromosome walking and high-density mapping in the present study, Pl18 was placed in a 0.7 cM interval on chromosome 2. A candidate gene HanXRQChr02g0048181 for Pl18 was identified from the XRQ reference genome and predicted to encode a protein with typical NLR domains for disease resistance. The Pl20 gene was placed in a 0.2 cM interval on chromosome 8. The putative gene with the NLR domain for Pl20, HanXRQChr08g0210051, was identified within the Pl20 interval. SNP markers closely linked to Pl18 and Pl20 were evaluated with 96 diverse sunflower lines, and a total of 13 diagnostic markers for Pl18 and four for Pl20 were identified. These markers will facilitate to transfer these new genes to elite sunflower lines and to pyramid these genes with broad-spectrum DM resistance in sunflower breeding.

Highlights

Downy mildew (DM) is a devastating sunflower disease throughout the world, in Europe and North America [1,2]
Most of the clusters are characterized as having nucleotide binding and leucine-rich repeat (NLR) motifs, which are the major class of disease-resistant genes found in flowering plants [14,15,16,17]
The predicted candidate genes for both Pl18 and Pl20 are NLR-type genes, which are strongly indicative of disease-resistant genes, as found in chickpea [18], soybean [19], maize [20], wheat [21], and rice [22]

Summary

Introduction

Downy mildew (DM) is a devastating sunflower disease throughout the world, in Europe and North America [1,2]. It is incited by the oomycete pathogen Plasmopara halstedii (Farl.) Berlese & de Toni, which could overwinter and persist in the soil for 5–10 years. Cool and moist soil favors downy mildew epidemics in sunflower fields. Sunflower is the field crop that was infected by this DM fungus, other susceptible plants of weeds in the Compositae family, such as marsh elder, could function as reservoirs for this soil-borne fungus (https://www.ag.ndsu.edu/extensionentomology/ recent-publications-main/publications/A-1331-sunflower-production-field-guide). DM infection is found mostly in the Northern Great Plains within the U.S, and the disease infected approximately 16% of sunflower fields in 2015 [3]. Substantial yield loss is expected upon DM infection, as severely infected plants will not proceed to growth at the seedling stage with few exceptions in which infected plants could still grow to maturity but not produce viable seeds

Methods

Results

Conclusion