Abstract
Wheat leaf rust (also known as brown rust), caused by the fungal pathogen Puccinia triticina Erikss. (Pt), is one by far the most troublesome wheat disease worldwide. The exploitation of resistance genes has long been considered as the most effective and sustainable method to control leaf rust in wheat production. Previously the leaf rust resistance gene Lr65 has been mapped to the distal end of chromosome arm 2AS linked to molecular marker Xbarc212. In this study, Lr65 was delimited to a 0.8 cM interval between flanking markers Alt-64 and AltID-11, by employing two larger segregating populations obtained from crosses of the resistant parent Altgold Rotkorn (ARK) with the susceptible parents Xuezao and Chinese Spring (CS), respectively. 24 individuals from 622 F2 plants of crosses between ARK and CS were obtained that showed the recombination between Lr65 gene and the flanking markers Alt-64 and AltID-11. With the aid of the CS reference genome sequence (IWGSC RefSeq v1.0), one SSR marker was developed between the interval matched to the Lr65-flanking marker and a high-resolution genetic linkage map was constructed. The Lr65 was finally located to a region corresponding to 60.11 Kb of the CS reference genome. The high-resolution genetic linkage map founded a solid foundation for the map-based cloning of Lr65 and the co-segregating marker will facilitate the marker-assisted selection (MAS) of the target gene.
Highlights
Anywhere wheat is cultivated, its production is seriously constrained by fungal pathogens, and most significantly by single or multiple of the three species of rust (Hovmøller et al, 2010), i.e., leaf rust (Puccinia triticina); stem rust (Puccinia graminis f. sp. tritici); and stripe rust (Puccinia striiformis f. sp. tritici)
When we matched the sequences of Alt-64 and AltID-11 with the genome sequence of Chinese Spring (CS) (IWGSC v1.0), we found that the two markers were spanning an area of about 0.34 Mb (555551– 891823) on CS chromosome 2AS (Figure 2D)
In order to confirm the usefulness of this Lr65 co-segregating marker in breeding, we tested marker 1500-1 on other 18 different Chinese wheat cultivars, we found that the polymerase chain reaction (PCR) product size of marker 1500-1 in Altgold containing Lr65 was unique and not detected in the other cultivars (Supplementary Figure 4); marker 1500-1 is diagnostic for selection of Lr65 gene
Summary
Anywhere wheat is cultivated, its production is seriously constrained by fungal pathogens, and most significantly by single or multiple of the three species of rust (Hovmøller et al, 2010), i.e., leaf rust (Puccinia triticina); stem rust (Puccinia graminis f. sp. tritici); and stripe rust (Puccinia striiformis f. sp. tritici). Leaf rust can cause a 15% production reduction and heavy infection can lead to losses of up to 40% (Knott, 1989; McMullen et al, 2008). Outbreaks of rust diseases have occurred in various regions of China, resulting in severe wheat yield reduction (Chen et al, 2018). Fine Mapping Leaf Rust Resistance the disease is based on improved varieties containing resistance genes (Keller et al, 2008). One of the most frustrating issues in disease resistance breeding is the failure of resistance genes, due to the evolving nature of plant pathogens resulting in new virulent races that can cause disease in formerly resistant wheat varieties. It is necessary to search for new diverse effective resistance genes that can be used in wheat breeding programs
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