QTL mapping of resistance to two wheat rust fungi, Puccinia triticina Eriks. and Puccinia striiformis Westend. in a multiparental wheat (Triticum aestivum L.) population

Abstract

With a global production of 766 million tons in 2019, wheat is the world's second most important cereal, providing ≥ 20 % of calories and protein for the human diet. Wheat rusts such as Puccinia striiformis f. sp. tritici and Puccinia triticina, the causal agents of stripe rust and leaf rust respectively, are among the most important fungal pathogens in wheat with the potential to cause severe yield and quality losses up to 70 %. Use of resistant cultivars is the economically safest and most environmentally friendly approach to avoid yield losses and ensure food security. However, the continuous development of new races of stripe rust and leaf rust that are virulent against important resistance genes increases the need for new sources of resistance. In recent years, the identification of quantitative trait loci (QTL) has become the basis of targeted breeding approaches aiming at increased and durable resistance in modern wheat cultivars. In addition, multiparent advanced generation intercross (MAGIC) populations have proven to be a powerful tool to carry out such genetic studies. In the framework of this thesis, the Bavarian MAGIC wheat population (BMWpop) was used to detect QTL conferring resistance against leaf rust and stripe rust. Seedling resistance was screened under controlled environmental conditions by using a detached leaf assay. Adult plant resistance was tested in multi-year’s field trials at three locations in Germany. Phenotypic data, together with genotypic data from the 15 K + 5 K Infinium® iSelect® array containing 17,267 single nucleotide polymorphisms (SNP), were used to perform simple interval mapping (SIM) for stripe rust and leaf rust resistance. In total, 19 QTL corresponding to 11 different regions on chromosomes 1A, 4A, 4D, 5A, 6B, 7A and 7D were identified in independent SIM studies for leaf rust resistance. Six of these regions may represent putative new QTL, which have not been described earlier. For stripe rust, 21 QTL corresponding to 13 distinct chromosomal regions were detected, of which two may represent putatively new QTL located on wheat chromosomes 3D and 7D. Peak markers of the identified QTL were partly directly annotated with genes known to be involved in quantitative resistance to leaf and stripe rust. Additional promising gene annotations with different functions in relation to resistance responses were identified when considering ± 500 kb around each peak marker of a QTL. The Bavarian MAGIC wheat population turned out to be well suited for the detection of QTL conferring resistance to leaf rust and stripe rust. Based on the phenotypic responses, RILs with increased resistance to both rust fungi were identified, which can be easily introduced into breeding programs due to their descent from elite parents.