Mapping for Adult-Plant Resistance Against Septoria Tritici Blotch in a Common Wheat Line Murga

Septoria tritici blotch (STB) is a major foliar disease globally that is notorious for quickly developing fungicide resistance, making host resistance an indispensable component in mitigating STB. The International Maize and Wheat Improvement Center (CIMMYT) wheat line Murga is well known for its high, durable, and broad-spectrum resistance against STB infection. This study aimed to investigate the resistance mechanism of Murga to facilitate its utilization in breeding. A recombinant inbred line population was derived from a cross between Murga and STB-susceptible line Huirivis#1, comprising 297 progenies. The population was evaluated for adult-plant STB resistance in Toluca, Mexico (from 2017 to 2019), and in La Estanzuela, Uruguay (from 2016 to 2018). Genotyping was performed with the DArTseq platform. Quantitative trait locus (QTL) mapping indicated a major and stable QTL on chromosome 3DL, explaining a phenotypic variation for STB of 41.2 to 62.5% in Mexico and 27.5 to 40.3% in Uruguay. This QTL was regarded as Stb16 based on the comparison of its physical position, the possible origin from synthetic wheat, and its broad-spectrum resistance. Additional QTLs with minor effects were identified on chromosomes 2B, 2D, 3A, 3B, and 5B. The QTL on 5BS was significant in four of the six environments and must be new. Murga was the resistant donor for all QTLs except for those on 2B and 3A. Being an elite breeding line, Stb16 carrier Murga could be used as a promising STB resistance donor. Rational employment of Stb16 could contribute to STB management yet avoid the rapid emergence of Stb16-virulent isolates.