Genetic Resistance to Fungal Pathogens in Sorghum [Sorghum Bicolor (L.) Moench]
Abstract
Sorghum [Sorghum bicolor (L.) Moench] is the fifth most widely grown cereal crop in the world that serves as a staple food for millions of people. Grain mold of sorghum, caused by a consortium of fungal pathogens, is a leading constraint to sorghum production. A second sorghum disease with significant economic impact is anthracnose caused by the ascomycete fungus Colletotrichum sublineolum(Cs). Grain mold causes yield reduction and is highly detrimental to food quality due to contamination by toxigenic fungi and mycotoxins while anthracnose results in significant yield reduction in susceptible cultivars. Genetic resistance is considered the only effective and sustainable way to control both diseases, but the genetic control of these diseases are not well understood. In this project, we implemented genetic, genomic and molecular approaches to identify loci and/or genes underlying resistance to the two diseases. The results presented in Chapters 2 to 5 provide new insights to the genetic and genomic architecture of resistance to grain mold and anthracnose. Chapter 1 provides background information and review of the literature on the pathology of the two diseases, the contrasting and shared mechanisms of genetic resistance and approaches to QTL and gene identification. Chapter 2 and Chapter 3 describe genome wide association studies (GWAS) conducted on sorghum landrace accessions from Ethiopia. Results of both sets of GWAS were recently published (Nida et al., 2019, Journal of Cereal Science 85, 295- 304; Nida et al., 2021, Theoretical Applied Genetics, https://doi.org/10.1007/s00122-020-03762- 2). Chapter 4 describes global transcriptome profiles of early stage of the developing grain from resistant and susceptible sorghum genotypes which uncovered process that correlate with resistance or susceptibility to grain mold. Finally, Chapter 5 summarizes two anthracnose resistance genes identified through whole genome resequencing and genetic mapping. In Chapter 2, genomic regions associated with grain mold resistance were identified through GWAS conducted using sorghum landraces. A major grain mold resistance locus containing tightly linked and sequence related MYB transcription factor genes were identified based on association between SNPs and grain mold resistance scores of 1425 accessions. The locus contains YELLOW SEED1 (Y1, Sobic.001G398100), a likely non-functional pseudo gene (Y2, Sobic.001G398200), and YELLOW SEED3 (Y3, Sobic.001G397900). SNPs and other sequence polymorphisms that alter the Y1 and Y3 genes correlated with susceptibility to grain mold and provided a strong genetic evidence. Although Y1has long been known as a regulator of kernel color and the biosynthesis of 3-deoxyanthocynidin phytoalexins, it was not annotated in the sorghum genome. The data suggest that the MYB genes and their grain and glume specific expressions determine responses to molding fungi. Chapter 3 focuses on GWAS conducted on a subset of early to medium flowering accessions to identify grain mold resistance loci. In addition, because of the caveats associated with grain flavonoid mediated mold resistance, we specifically aimed to identify resistance loci independent of grain flavonoids. A multi-environment grain mold phenotypic data and 173,666 SNPs were used to conduct GWAS using 635 accessions and a subset of non-pigmented accessions, potentially producing no tannins and/or phenols.
Degree
Ph.D.
Advisors
Mengiste, Purdue University.
Subject Area
Genetics
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