Identification and characterization of sources of genetic resistance to wheat diseases in Ethiopian landraces and in the Ethiopian durum wheat NAM (EtNAM) population

Septoria tritici blotch, leaf rust and yellow rust are devastating foliar diseases of durum wheat worldwide. The most economical and environmentally sound method to reduce the risk of yield loss due to these diseases are to use cultivars with durable genetic resistance. However, few cultivars with adequate resistance are available to date. The first purpose of this PhD project was to exploit the phenotypic and molecular diversity of untapped Ethiopian durum wheat germplasm to identify genetic loci relevant to STB resistance. Ethiopian durum wheat landraces represent a valuable source of such diversity. In this study, 318 Ethiopian durum wheat genotypes, for the most part traditional landraces, were phenotyped for resistance to different aspects of STB infection. Ethiopian durum wheat landraces shown diverse STB resistance levels, allowing for a genome wide association study (GWAS). In this research, we detected five major putative QTL for STB resistance. Our results show that the Ethiopian untapped allelic diversity bears a great value in studying STB and other disease resistance. The second aim of this thesis was to characterize a large Ethiopian durum wheat NAM (EtNAM), a genetic mapping resource built by the intercross of a modern variety with international pedigree with Ethiopian traditional materials. A subset of 12 EtNAM families, 100 recombinant inbred lines (RILs) each, was genotyped with a high-density genotyping array, allowing the characterization of the genetic diversity and structure of the population. We argue that the EtNAM may act as a breeding tool and a research tool, supporting the identification of QTL of disease resistance relevance and their incorporation in pre-breeding materials. In this study, we characterized a subset of the EtNAM population, and shown it is highly diverse. Using molecular and phenotypic data, we described how the EtNAM RILs were successfully closing the gap between local and international allele pools. Marker data produced on the EtNAM was projected on the wild emmer genome sequence and was used to characterize the genetic features of the population. The EtNAM shows high minor allele frequency and a fast linkage disequilibrium decay, suggesting elevated QTL mapping power and definition. This study is the first to describe an advanced multiparental population build with Ethiopian durum wheat. The information that we have generated is also valuable to identify QTL for important agronomic and diseases resistance traits. Based on the genomic diversity of the EtNAM population, we have characterized its phenotypic diversity in different environments for STB, leaf rust and yellow rust. We found that the EtNAM population had a wide range of resistance levels to STB, leaf rust and yellow rust. The mean values of RILs in each family were close to the average of the female and male parents, confirming that resistance to STB, leaf rust and yellow rust are under polygenic control combined with an additive effect. This high phenotypic diversity present within and among the EtNAM families, is important for identify QTLs for STB, leaf rust and yellow rust resistance. Finally, we approached the detection of QTL for STB, leaf rust and yellow rust resistance in the EtNAM population. The EtNAM RILs were used in a GWAS that allowed the identification of 70 marker trait associations (MTAs) for all the considered. Many of the QTL discovered reported resistance loci for each disease. The EtNAM population offers sources for multiple resistance alleles, which can be useful for gene pyramiding for durum wheat breeding. Pyramiding putative resistant alleles for resistance to several diseases had been successfully utilized in various crops. In this sense, the EtNAM may be exploited for durable resistance for durum wheat breading, and represent a promising tool for modern durum wheat production in Ethiopia.