Characterization and Mapping of Leaf Rust and Stripe Rust Resistance Loci in Hexaploid Wheat Lines UC1110 and PI610750 under Mexican Environments

Abstract

Growing resistant wheat varieties is a key method of minimizing the extent of yield losses caused by the globally important wheat leaf rust (LR) and stripe rust (YR) diseases. In this study, a population of 186 F₈ recombinant inbred lines (RILs) derived from a cross between a synthetic wheat derivative (PI610750) and an adapted common wheat line (cv. "UC1110") were phenotyped for LR and YR response at both seedling and adult plant stages over multiple seasons. Using a genetic linkage map consisting of single sequence repeats and diversity arrays technology markers, in combination with inclusive composite interval mapping analysis, we detected a new LR adult plant resistance (APR) locus, QLr.cim-2DS, contributed by UC1110. One co-located resistance locus to both rusts, QLr.cim-3DC/QYr.cim-3DC, and the known seedling resistance gene Lr26 were also mapped. QLr.cim-2DS and QLr.cim-3DC showed a marginally significant interaction for LR resistance in the adult plant stage. In addition, two previously reported YR APR loci, QYr.ucw-3BS and Yr48, were found to exhibit stable performances in rust environments in both Mexico and the United States and showed a highly significant interaction in the field. Yr48 was also observed to confer intermediate seedling resistance against Mexican YR races, thus suggesting it should be re-classified as an all-stage resistance gene. We also identified 5 and 2 RILs that possessed all detected YR and LR resistance loci, respectively. With the closely linked molecular markers reported here, these RILs could be used as donors for multiple resistance loci to both rusts in wheat breeding programs.

Keywords: adult plant resistance; durable rust resistance; leaf rust; stripe rust; wheat.

FIGURE 1

Genetic linkage map of chromosome 5A showing the location of the all-stage resistance gene Yr48. Locus names and corresponding locations on the genetic map are indicated on the right side. Map distances in cM are shown on the left side. Markers co-segregating with Yr48 are given in bold.

FIGURE 2

Frequency distributions of stripe rust response for UC1110/PI610750 recombinant inbred lines (RILs) possessing and lacking Yr48 at the seedling stage (A) and the adult plant stage (B).

FIGURE 3

Frequency distributions of UC1110/PI610750 recombinant inbred lines (RILs) for final leaf rust severity in field trials (A) at Ciudad Obregón in 2012 (LR2012Y, (B) at El Batán in 2012 (LR2011B), and (C) at El Batán in 2013 (LR2012B). The leaf rust severities for PI610750 and UC1110 are indicated by arrows.

FIGURE 4

Frequency distributions of UC1110/PI610750 recombinant inbred lines (RILs) for final stripe rust severity in field trials (A) at Toluca in 2012 (YR2012) and (B) at Toluca in 2013 (YR2013). The stripe rust severities for PI610750 and UC1110 are indicated by arrows.

FIGURE 5

LOD plots of quantitative trait loci (QTL) for adult plant resistance to leaf rust on chromosomes 2DS (A) and to both leaf and stripe rust on chromosome 3DC (B), identified using IciMapping 4.1 in the UC1110/PI610750 RIL population. Significant LOD were detected based on 1,000 permutations. Positions (cM) of the molecular markers on chromosomes are shown on the vertical axes; cumulative genetic distances of linkage groups are also shown. LR12Y, LR12B, and LR13B: leaf rust phenotypic data at Ciudad Obregón in 2012 and El Batán during 2012 and 2013, respectively; YR12: stripe rust phenotypic data at Toluca in 2012; LR12AY, LR12AB, LR13AB, and YR12A: area under the disease progress curve (AUDPC); LRM and YRM: mean final disease severity over test environments. QTL flanking markers are in bold.

FIGURE 6

Comparison of UC1110/PI610750 recombinant inbred lines (RILs) for mean final leaf rust severity in the presence (+) and absence (–) of the leaf rust resistance QTL Lr.cim-2DS over 3 years of field trials. The numbers of RILs in each category are shown in parentheses.