Increased experimental conditions and marker densities identified more genetic loci associated with southern and northern leaf blight resistance in maize

Yong-Xiang Li,Yanchun Song,Yu Li,Zhiwu Zhang,Tianyu Wang,Yun-Su Shi,Peter J Bradbury,Chunhui Li,Edward S Buckler,Lin Chen,Dengfeng Zhang

doi:10.1038/s41598-018-25304-z

Abstract

Southern leaf blight (SLB) and northern leaf blight (NLB) are the two major foliar diseases limiting maize production worldwide. Upon previous study with the nested association mapping (NAM) population, which consist of 5,000 recombinant inbred lines from 25 parents crossed with B73, we expanded the phenotyping environments from the United States (US) to China, and increased the marker densities from 1106 to 7386 SNPs for linkage mapping, and from 1.6 to 28.5 million markers for association mapping. We identified 49 SLB and 48 NLB resistance-related unique QTLs in linkage mapping, and multiple loci in association mapping with candidate genes involved in known plant disease-resistance pathways. Furthermore, an independent natural population with 282 diversified inbred lines were sequenced for four candidate genes selected based on their biological functions. Three of them demonstrated significant associations with disease resistance. These findings provided valuable resources for further implementations to develop varieties with superior resistance for NLB and SLB.

Highlights

Southern leaf blight (SLB), caused by the fungus Cochliobolus heterostrophus, and northern leaf blight (NLB), caused by the fungus Exserohilum turcicum, are two major foliar diseases that can lead to serious yield loss in maize-growing regions worldwide[1,2]
Through a genome-wide association study (GWAS) of the maize nested association mapping (NAM) population, multiple candidate genes involved in basal defence against SLB and NLB were identified, which suggested that quantitative disease resistance (QDR) in plants is conditioned by a range of mechanisms, including basal resistance[26,27]
Among the 5,000 recombinant inbred lines (RILs), 4694 RILs were scored for the SLB under one naturally inoculated environment and two artificially inoculated environments in the United States (US)[26]

Summary

Introduction

Southern leaf blight (SLB), caused by the fungus Cochliobolus heterostrophus, and northern leaf blight (NLB), caused by the fungus Exserohilum turcicum, are two major foliar diseases that can lead to serious yield loss in maize-growing regions worldwide[1,2]. A better understanding of the relationship between R-genes and QRLs would contribute to crop disease management, for diseases caused by necrotrophic pathogens. Both SLB and NLB are caused by necrotrophic pathogens; these pathogens depend on killing host cells and living in the dead tissue. Through a genome-wide association study (GWAS) of the maize NAM population, multiple candidate genes involved in basal defence against SLB and NLB were identified, which suggested that QDR in plants is conditioned by a range of mechanisms, including basal resistance[26,27].

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Conclusion