Development of a molecular marker for the Run8 gene for the selection of barley genotypes resistant to smut

Loose smut of barley, caused by the basidiomycete Ustilago nuda (Jens.) Roster, occurs in all regions of the world where this crop is grown. This seed-borne disease causes significant losses in grain production. Selection for resistance to loose smut based on the use of donors with resistance genes is an ecologically and economically safe way to constrain the negative impact of the pathogen on barley. The introduction of molecular genetic approaches into the breeding process makes it possible to control the transfer of resistance genes to hybrid material. The Run8 gene controls resistance to many isolates of loose smut, including in the West Siberian region of Russia. The objective of the current study is to develop a molecular marker for Run8 for the selection of barley genotypes resistant to loose smut from hybrid populations. By comparing the nucleotide sequences of the Run8 gene available from the barley pangenome database, an insertion/deletion of six nucleotide pairs in the coding region of the gene was identified. Based on the identified polymorphism, a molecular marker Hor7050 was developed, which allows differentiating the alleles of Run8. The developed marker was tested on hybrid lines (F5-F6) obtained from crossing cultivar Elf, which is a donor of resistance to loose smut and carries, according to the originators, the Run8 gene, with cultivar Tanai, which has practical resistance to the pathogen. Using the developed marker, 18 hybrids carrying Run8 of Elf were selected from 84 hybrids; however, the phytopathological assessment showed that eight of the selected lines were susceptible to the disease. To clarify the genotype of 18 selected lines, an additional analysis was carried out using the microsatellite marker EBmac0541 linked to Run6. A relationship was established between the presence of the allele of this marker from Elf and resistance to the disease. It is possible that Elf, in addition to Run8, carries Run6, which is effective against race 1 of the causative agent of loose smut. Additional studies are required to clarify the presence of Run6 in the Elf variety. In addition to resistance, the selected lines were characterized by productivity traits. According to the two-year analysis, three productive resistant lines were identified, with Run8 - 32, 65 and 79, significantly exceeding the control Elf in yield. The selected lines were transferred to breeding nurseries for their further evaluation by economically important traits.