Linkage of Lr55 wheat leaf rust resistance gene with microsatellite and DArT-based markers

Highlights

• Two F₂ mapping populations Bogatka × KS04WGRC45 and Nadobna × KS04WGRC45 were developed in order to identify the molecular marker(s) linked to the Lr55 gene

• ∙In total the segregations of 22 microsatellite and 7 DArT-based markers were used to create linkage groups corresponding to 1B chromosomes in individual mapping populations

• ∙At consensus map, Lr55 gene was flanked by XGwm374 and XWmc406 markers at distance of 8.3 and 14.8 cM

• ∙The molecular markers developed may be a starting point for the selection of plant materials for the presence of the Lr55 gene

Abstract

Every year, leaf rust causes losses of wheat yield and quality all around the world. Breeding of cereals resistant to fungal diseases offers a long-term alternative for chemical protection and becomes increasingly important for organic farming and ecological food production. Accumulation of effective resistance genes in a single genotype requires recurrent enrichment of the wheat genepool with promising resistance alleles marked with DNA tags. Lr55 gene was transferred to KS04WGRC45 wheat from Elymus trachycaulus and provides effective resistance to leaf rust. Two F₂ mapping populations Bogatka × KS04WGRC45 (BK) and Nadobna × KS04WGRC45 (NK) were developed in order to identify the molecular marker(s) linked to the Lr55 gene. In total the segregations of 22 microsatellite and 7 DArT-based markers were used to create linkage groups corresponding to 1B chromosomes in individual mapping populations. At consensus map, Lr55 gene was flanked by XGwm374 and XWmc406 markers at distance of 8.3 and 14.8 cM, respectively. Until now, no molecular markers have been reported for Lr55 gene, and the molecular markers developed may be a starting point for the selection of plant materials for the presence of the Lr55 gene. However, additional marker systems based on next-generation sequencing may be necessary for more accurate location of Lr55 gene location.

Introduction

Leaf rust caused by the fungus Puccinia triticina (syn. P. recondita Rob. ex Desm. f. sp. tritici) is one of the most serious fungal diseases of wheat [1]. The disease occurs each year and causes losses in both yield quantity and quality. Generally, the yield losses of winter wheat vary between 1 and 20% [2]. Occasionally, under optimal conditions for pathogen development and with strong infestation by P. triticina, the losses can reach up to 40–60% [[3], [4], [5]]. In response to global climate warming, significance of leaf rust is expected to increase thanks to the earlier start of first symptoms and extended period for secondary infections [1,6,7].

Over 80 leaf rust resistance (Lr) genes have been identified so far, of which more than 70 have been juxtaposed in the wheat gene catalogue [[8], [9], [10], [11]]. Intraspecific variation provides a primary source of Lr genes for common wheat. Within this genepool, some Lr genes turned out to be allelic, i.e: Lr21 = Lr40, Lr39 = Lr41 [12,13]. Wild and related species are a secondary genepool and a source of effective leaf rust resistance genes for common wheat. Lr genes were transferred from alien species through recombination between homologous or homeologous chromosomes, and by translocating intact chromosomal fragments from more distant species. The Lr55 gene comes from the Persian species Elymus trachycaulus and gives resistance to P. triticina both in the seedling and mature stages [14].

Resistance breeding is in line with the development of organic farming and leads to the reduction of chemical plant protection. In wheat, the most commonly used strategy for breeding of P. triticina resistant lines is accumulating race-specific effective resistance genes on background of slow rusting genes. This strategy provides full but usually short-term resistance that is broken down by the emergence of new pathotype races of P. triticina [[15], [16], [17], [18]]. Recently, genes Lr9, Lr10, Lr19, Lr24, Lr28, Lr32 were reported as effective resistance genes for P. triticina in Poland [19]. The search for effective sources of resistance genes is significant for genepool enrichment, control and breeding resistant varieties [20]. Although Lr55 gene has not been extensively used so far, it seems to be an effective gene for resistance to leaf rust. The immune response (score 0 or 0) of the KS04WGRC45 line, which is the source of the Lr55 gene, was observed under controlled conditions in both the seedling and mature (adult) stages for 15 differential isolates (own observations, unpublished data).

The accumulation of beneficial alleles accompanying the increased tolerance to leaf rust using DNA markers corresponds to the strategy of breeding high and stable yielding wheat varieties. The use of genetic markers in resistance breeding allows to combine multiple effective genes in a single genotype and leads to increased sustainability of the tolerance effects. Therefore, the identification of Lr gene markers is a prerequisite for the systematic accumulation of selected Lr genes. This research was aimed at the identification of molecular markers linked with the Lr55 gene that was introduced on 1BL.1H^tS translocation to two common wheat varieties.