No abstract

A compensating, recombined Lr59 translocation with greatly reduced alien chromatin was identified. Microsatellite locus Xdupw217 occurs within the remaining segment and can be used as a co-dominant marker for Lr59. In earlier studies, leaf rust (caused by Puccinia triticina Eriks.) resistance gene Lr59 was transferred from Aegilops peregrina (Hackel) Maire et Weiler to chromosome arm 1AL of common wheat (Triticum aestivum L.). The resistance gene was then genetically mapped on the translocated chromosome segment following homoeologous pairing induction. Eight recombinants that retained the least alien chromatin apparently resulted from crossover within a terminal region of the translocation that was structurally different from 1AL. These recombinants could not be differentiated by size, and it was not clear whether they were compensating in nature. The present study determined that the distal part of the original translocation has group 6 chromosome homoeology and a 6BS telomere (with the constitution of the full translocation chromosome being 1AS·1L(P)·6S(P) ·6BS). During the allosyndetic pairing induction experiment to map and shorten the full size translocation, a low frequency of quadrivalents involving 1A, the 1A translocation, and two 6B chromosomes was likely formed. Crossover within such quadrivalents apparently produced comparatively small compensating alien chromatin inserts within the 6BS satellite region on chromosome 6B of seven of the eight recombinants. It appears that the Gli-B2 storage protein locus on 6BS has not been affected by the recombination events, and the translocations are therefore not expected to affect baking quality. Simple sequence repeat marker results showed that Lr59-151 is the shortest recombinant, and it will therefore be used in breeding. Marker DUPW217 detects a homoeo-allele within the remaining alien chromatin that can be used for marker-assisted selection of Lr59.

Cadmium (Cd) is a heavy metal that has no known biological function and is toxic for many living organisms. The maximum level of Cd concentration allowed in the international market for wheat grain is 0.2 mg kg−1. Because phenotyping for Cd uptake is expensive and time consuming, molecular markers associated with genes conferring low Cd uptake would expedite selection and lead to the development of durum cultivars with reduced Cd concentrations. Here, we identified single nucleotide polymorphisms (SNPs) associated with a novel low Cd uptake locus in the durum experimental line D041735, which has hexaploid common wheat in its pedigree. Genetic analysis revealed a single major QTL for Cd uptake on chromosome arm 5BL within a 0.3 cM interval flanked by SNP markers. Analysis of the intervening sequence revealed a gene with homology to an aluminum-induced protein as a candidate gene. Validation and allelism tests revealed that the low Cd uptake gene identified in this study is different from the closely linked Cdu1-B gene, which also resides on 5BL. This study therefore showed that the durum experimental line D041735 contains a novel low Cd uptake gene that was likely acquired from hexaploid wheat.

Stem rust, caused by Puccinia graminis f. sp. tritici (Pgt) is an economically important disease of wheat and barley. Rpg1 is the only resistance gene deployed in Midwestern US barley varieties and provides remarkable resistance to most North American races, except Pgt race QCCJB. Rpg1 is also ineffective against Pgt race TTKSK and its lineage that originated in Africa. The barley rpg4-mediated resistance locus (RMRL) conferring resistance to Pgt races QCCJB and TTKSK was isolated from line Q21861, which is resistant to all known Pgt races due to Rpg1 and RMRL. To develop elite barley varieties RMRL was pyramided into the varieties, Pinnacle and Conlon (both contain Rpg1), producing the near isogenic lines (NILs), Pinnacle RMRL-NIL (PRN) and Conlon RMRL-NIL (CRN). The CRN was resistant to Pgt races QCCJB (RMRL specific) and HKHJC (Rpg1 specific) at the seedling stage and Pgt race TTKSK (RMRL specific) at the adult stage. In contrast, PRN was susceptible to QCCJB and HKHJC at the seedling stage and TTKSK at the adult stage. Interestingly, PRN’s susceptibility to QCCJB and HKHJC showed that RMRL was non-functional in the Pinnacle background but its presence also suppressed Rpg1-mediated resistance. Thus, in the absence of a gene/s found in the Q21861 background, Rpg1 becomes non-functional if RMRL is present, suggesting that another polymorphic gene, that we designated Rrr1 (required for rpg4-mediated resistance 1), is required for RMRL resistance and Rpg1-mediated resistance in the presence of RMRL. Utilizing a PRN/Q21861 derived recombinant inbred line (RIL) population, Rrr1 was delimited to a ∼0.5 MB physical region, slightly proximal (∼1.8 MB) of RMRL on barley chromosome 5H. A second gene, designated required for Rpg1-mediated resistance 2 (Rrr2), with duplicate gene action to Rrr1 in Rpg1-mediated resistance function, was genetically delimited to a physical region of ∼0.7 MB, slightly distal (∼3.1 MB) to Rpg1 on the short arm of barley chromosome 7H. Thus, Rrr1 is required for RMRL resistance and Rrr1 or Rrr2 is required for functional Rpg1-mediated resistance in the presence of the RMRL introgression. Candidate Rrr1 and Rrr2 genes were identified that need to be considered when pyramiding Rpg1 and RMRL in barley.