Abstract
Genetic resistance in the host plant is the most economical and environmentally friendly strategy for controlling wheat leaf rust, caused by Puccinia triticina Eriks. The durum wheat lines Gaza (Middle East), Arnacoris (France) and Saragolla (Italy) express high levels of resistance to the Mexican races of P. triticina. Three recombinant inbred line (RIL) populations, derived from crosses of each of these resistance sources to the susceptible line ATRED #2, were evaluated for leaf rust reactions at CIMMYT’s leaf rust nurseries in Mexico. Genetic analyses of host reactions suggested oligogenic control of resistance in all populations. The F8 RILs from each cross were genotyped using the Illumina iSelect 90K array, and high-density genetic maps were constructed for each population. Using composite interval mapping, a total of seven quantitative trait loci (QTL) that provide resistance to leaf rust were identified. Two QTL designated as QLr.usw-6BS and QLr.usw-6BL were identified on chromosome 6B in Gaza, which explained up to 78.5% and 21.3% of the observed leaf rust severity variance, respectively. A major QTL designated as QLr.usw-7BL was detected on the long arm of chromosome 7B in Arnacoris, which accounted for up to 65.9% of the disease severity variance. Arnacoris also carried a minor QTL on chromosome 1BL, designated as QLr.usw-1BL.1 that explained up to 17.7% of the phenotypic variance. Three QTL conferred leaf rust resistance in Saragolla, namely QLr.usw-2BS, QLr.usw-3B, and QLr.usw-1BL.2, which accounted for up to 42.3, 9.4, and 7.1% of the phenotypic variance, respectively. Markers flanking each QTL were physically mapped against the durum wheat reference sequence and candidate genes involved in disease resistance were identified within the QTL intervals. The QTL identified in this study and their closely linked markers are useful resources for gene pyramiding and breeding for durable leaf rust resistance in durum wheat.
Highlights
IntroductionThe importance of leaf rust as a threat to global durum wheat (Triticum turgidum L. ssp durum) production has increased dramatically during the last decade, due to the occurrence of highly virulent races of Puccinia triticina and the breakdown of the resistance genes that were widely deployed (Singh et al, 2004; Huerta-Espino et al, 2011; Herrera-Foessel et al, 2014a; Kolmer, 2015b; Soleiman et al, 2016; Kolmer and Hughes, 2017)
The recombinant inbred line (RIL) from the three mapping populations expressed a wide range in disease severity, with the resistant parents Gaza, Arnacoris, and Saragolla showing the lowest scores for leaf rust severity (0–5%), and the highest scores (90–100%) being observed on the susceptible parent ATRED #2
No transgressive segregation was observed among the RILs from the three crosses, which confirmed that the susceptible parent ATRED #2 does not contribute any genes for leaf rust resistance that could be detected under the present phenotyping conditions
Summary
The importance of leaf rust as a threat to global durum wheat (Triticum turgidum L. ssp durum) production has increased dramatically during the last decade, due to the occurrence of highly virulent races of Puccinia triticina and the breakdown of the resistance genes that were widely deployed (Singh et al, 2004; Huerta-Espino et al, 2011; Herrera-Foessel et al, 2014a; Kolmer, 2015b; Soleiman et al, 2016; Kolmer and Hughes, 2017). Resistance to wheat leaf rust is commonly categorized into two classes based on their genetic control and phenotypic effect: race-specific, allstage resistance, which is usually expressed as a hypersensitive response leading to host cell death, and adult plant resistance (APR), which is usually expressed as a slow-rusting phenotype (Knott, 1989; Lagudah, 2011; Kolmer, 2013; Singh et al, 2016). Most Lr genes have major effects and confer race-specific, all-stage near-immunity. This class of resistance is prone to rapid breakdown as the pathogen population evolves, and new virulent races emerge (Suenaga et al, 2003; Huerta-Espino et al, 2011; Lowe et al, 2011; Ellis et al, 2014; Herrera-Foessel et al, 2014b). Lr46 has been reported in durum wheat (T. turgidum L. ssp. durum) (Herrera-Foessel et al, 2011)
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