Genetic Analysis Using a Multi-Parent Wheat Population Identifies Novel Sources of Septoria Tritici Blotch Resistance

Abstract

Zymoseptoria tritici is the causative fungal pathogen of septoria tritici blotch (STB) disease of wheat (Triticum aestivum L.) that continuously threatens wheat crops in Ireland and throughout Europe. Under favorable conditions, STB can cause up to 50% yield losses if left untreated. STB is commonly controlled with fungicides; however, a combination of Z. tritici populations developing fungicide resistance and increased restrictions on fungicide use in the EU has led to farmers relying on fewer active substances. Consequently, this serves to drive the emergence of Z. tritici resistance against the remaining chemistries. In response, the use of resistant wheat varieties provides a more sustainable disease management strategy. However, the number of varieties offering an adequate level of resistance against STB is limited. Therefore, new sources of resistance or improved stacking of existing resistance loci are needed to develop varieties with superior agronomic performance. Here, we identified quantitative trait loci (QTL) for STB resistance in the eight-founder "NIAB Elite MAGIC" winter wheat population. The population was screened for STB response in the field under natural infection for three seasons from 2016 to 2018. Twenty-five QTL associated with STB resistance were identified in total. QTL either co-located with previously reported QTL or represent new loci underpinning STB resistance. The genomic regions identified and the linked genetic markers serve as useful resources for STB resistance breeding, supporting rapid selection of favorable alleles for the breeding of new wheat cultivars with improved STB resistance.

Keywords: MAGIC population; SNP genotyping array; genetic disease resistance; quantitative trait locus (QTL) mapping; r/qtl2; septoria tritici blotch; wheat.

Figure 1

Septoria tritici blotch (STB) disease of wheat in a field trial in Carlow, Ireland, showing the resulting necrosis of the leaves within the crop canopy.

Figure 2

Genetic map locations (centiMorgan - cM) of septoria tritici blotch (STB) QTL detected in the “NIAB Elite MAGIC” population. QTL locations and interval sizes are indicated by the green bars on the right-hand side of each chromosome and are based on the genetic marker information in Table 5. The genetic map locations are based on the “NIAB Elite MAGIC” genetic map [68]. The QTL name assigned in this study (presented in Table 5) is followed by the environment in which the QTL was detected.

Figure 3

Physical map locations (megabase pair—Mbp) of septoria tritici blotch (STB) QTL detected in the current study compared to previously reported QTL. QTL locations and interval sizes are indicated by bars on the right-hand side of each chromosome and are based on the physical map information in Table 5 and Table S5. The physical map location was based on the wheat cv. Chinese Spring IWGSC RefSeq v1.0 genome assembly (IWGSC, 2018). The QTL name assigned in this study (presented in Table 5; green colour) is followed by the environment in which the QTL was detected. Previously reported QTL are indicated in blue, where the displayed QTL are only defined on the physical map by anchoring one of the two flanking makers indicated by a “*”.

Figure 3

Physical map locations (megabase pair—Mbp) of septoria tritici blotch (STB) QTL detected in the current study compared to previously reported QTL. QTL locations and interval sizes are indicated by bars on the right-hand side of each chromosome and are based on the physical map information in Table 5 and Table S5. The physical map location was based on the wheat cv. Chinese Spring IWGSC RefSeq v1.0 genome assembly (IWGSC, 2018). The QTL name assigned in this study (presented in Table 5; green colour) is followed by the environment in which the QTL was detected. Previously reported QTL are indicated in blue, where the displayed QTL are only defined on the physical map by anchoring one of the two flanking makers indicated by a “*”.