Defeating the Warrior: genetic architecture of triticale resistance against a novel aggressive yellow rust race

Abstract

Genome-wide association mapping of resistance against the novel, aggressive 'Warrior' race of yellow rust in triticale revealed a genetic architecture with some medium-effect QTL and a quantitative component, which in combination confer high levels of resistance on both leaves and ears. Yellow rust is an important destructive fungal disease in small grain cereals and the exotic 'Warrior' race has recently conquered Europe. The aim of this study was to investigate the genetic architecture of yellow rust resistance in hexaploid winter triticale as the basis for a successful resistance breeding. To this end, a diverse panel of 919 genotypes was evaluated for yellow rust infection on leaves and ears in multi-location field trials and genotyped by genotyping-by-sequencing as well as for known Yr resistance loci. Genome-wide association mapping identified ten quantitative trait loci (QTL) for yellow rust resistance on the leaves and seven of these also for ear resistance. The total genotypic variance explained by the QTL amounted to 44.0% for leaf and 26.0% for ear resistance. The same three medium-effect QTL were identified for both traits on chromosomes 1B, 2B, and 7B. Interestingly, plants pyramiding the resistance allele of all three medium-effect QTL were generally most resistant, but constitute less than 5% of the investigated triticale breeding material. Nevertheless, a genome-wide prediction yielded a higher predictive ability than prediction based on these three QTL. Taken together, our results show that yellow rust resistance in winter triticale is genetically complex, including both medium-effect QTL as well as a quantitative resistance component. Resistance to the novel 'Warrior' race of this fungal pathogen is consequently best achieved by recurrent selection in the field based on identified resistant lines and can potentially be assisted by genomic approaches.

Genetic resistance to stripe rust infection of the wheat ear is controlled by genes controlling foliar resistance and flowering time

“…This difference in heritability is in agreement with YR resistance studies in Triticale (a hybrid between wheat and rye) that also report lower heritability in ears compared to leaves (Losert et al 2017). Furthermore, Losert et al (2017) argue that the severe ear infection they observed in Triticale may have been a feature of the prevalent Pst 'Warrior' race and its potential ability to develop at warmer temperatures.…”

QTL mapping for the resistance to yellow rust race CYR34 in triticale

“…The data presented herein are crucial for the breeding of new triticale varieties resistant to CYR34. However, only six QTLs associated with CYR34 were identified, which is fewer than the QTLs related to 'Warrior' detected by Losert et al (2017). In contrast to wheat with its much broader germplasm pool, triticale breeding can currently only exploit the Yr loci available within this man-made crop.…”

“…QTLs mapping for resistance to the yellow rust race CYR34 QTL mapping approaches can be employed to dissect the genetic architecture underlying complex traits and to identify QTL for marker-assisted selection programs (Alheit et al, 2014). Using genome wide association mapping in triticale, Losert et al (2017) identified 10 QTLs for resistance to the yellow rust pathogen race 'Warrior' on leaves, seven of them were responsible for ear resistance. The exotic 'Warrior' race has conquered Europe in recent years.…”

“…Takagi et al (2013) identified QTLs for partial resistance to rice blast disease and seedling vigour in recombinant inbred lines and F2 populations of rice using QTL-seq. Studies on the location of genes mediating yellow rust resistance have mainly focused on staple crops, the resistance to yellow rust race 'Warrior' in triticale has been reported (Losert et al, 2017), and there were no studies on triticale QTLs for resistance to yellow rust race CYR34.…”

Candidate Genes Underlying QTL for Powdery Mildew Resistance in Triticale (x Triticosecale Wittm.)

“…stem and leaf rust and Fusarium head blight (FHB). The most important, triticale become vulnerable to powdery mildew (Losert et al 2017;Galiano-Carneiro et al 2019) that may lead to signi cant economic losses (Arseniuk and Góral 2015;Mergoum et al 2019).…”