*laura.ziems@sydney.edu.au

Generating populations for mapping quantitative trait loci (QTL) is typically a time consuming and expensive process. Where possible pre-existing germplasm and genetic data should be revisited to extract additional value through both assessments for new traits and or exploring alternative mapping strategies. In wheat biotic stress resistance genetics, there is often a standard susceptible genotype that is used to map genes donated from resistant parents.

This occurs for several reasons, crossing compatibility and reliability of the line, agronomically desirable background for delivery to breeders etc. As reference parents are continuously adopted, they become well characterised and more likely to be selected in the future. This results in the development of numerous bi parental populations with a common parent, designed to map the same foliar disease. These populations can be combined and assessed together as a nested association mapping population.

The aim of this study was to identify novel ‘modifiers’ enhancing durable APR genes. Three (F7) wheat stripe rust (WYR) mapping populations; ARZ/AvocetS [n = 146], West Savla 68/AvocetS [n = 110] and Kazouria Talian/AvocetS [n = 97] assessed for adult plant resistance (APR) to stripe rust in 2018 (employing pts. 150, 134, 239) and 2019 (pts. 110, 150, 134, 198) were further investigated. A total of 4,966 tGBS AgriBio markers positioned on the IWGSC Chinese Spring assembly v1.0 were available.

The genotypic diversity of the population was assessed and clustering into distinct families was observed. AvocetS, the common parent among the families is a stripe rust susceptible, whereas resistance donors are known carriers of APR to WYR; ARZ and Kazouria Talian carrying Yr46 (4D) and West Savla 68 carrying Yr18 (7D). The donors were observed presenting low infection types across both years of assessment with the prevalent most virulent pathotypes.

Three approaches; bi-parental mapping (QTL cartographer), genome wide association analysis (rrBLUP) and nested association mapping (StatgenMPP) were used to analyse the populations. Both known (Yr18 and Yr46) and novel genes for APR were detected. KASP markers were developed for the novel region on 5A ~673-677 Mbp consistently detected across the three strategies. This study highlights the potential for optimizing QTL mapping processes by revisiting pre-existing germplasm and genetic data, thus maximizing the value of previous findings and investments.