Complementary resistance genes in wheat selection ‘Avocet R’ confer resistance to stripe rust

Abstract

Complementary genes for resistance to wheat stripe rust in an Avocet selection mapped to chromosome arms 3DL and 5BL. Susceptible Avocet selections lacked the 5BL gene due to a chromosomal deletion. This study reports the inheritance and genetic mapping of the YrA (temporary name of convenience to describe the specificity) seedling resistance to wheat stripe rust (caused by Puccinia striiformis f. sp. tritici; Pst) in a resistant selection of the Australian cv. Avocet [Avocet R (AvR)-AUS 90660]. Genetic analysis was performed on F2 populations and F3 generation families from crosses between wheats that carried and lacked the YrA resistance. Greenhouse seedling tests with two avirulent Pst pathotypes (104 E137 A- and 108 E141 A-) confirmed that the YrA resistance was inherited as two complementary dominant genes. Ninety-two doubled haploid (DH) lines from a cross between the Australian cv. Teal (Pst susceptible) and AvR were used for DArT-Seq genotypic analysis to map the seedling resistance. Marker-trait association analysis using 9035 DArT-Seq loci mapped the genes to the long arms of chromosomes 3D (3DL) and 5B (5BL), respectively. F2 populations from crosses between susceptible DH lines that carried either the 3DL or 5BL marker genotypes confirmed the complementary gene model. Fluorescence in situ hybridization (FISH) analysis determined that Teal carries a reciprocal T5B-7B translocation. FISH analysis also identified a 5BL chromosomal deletion in Avocet S relative to AvR that further validated the complementary gene model and possibly explained the heterogeneity of closely related wheats carrying the YrA resistance. The individual loci of the complementary YrA resistance were designated Yr73 (3DL) and Yr74 (5BL). Candidate single gene reference stocks will be permanently accessioned following cytological analysis to avoid the T5B-7B translocation.

Identification and evaluation of resistance to powdery mildew and yellow rust in a wheat mapping population

“…Qualitative resistance is generally conferred by single genes with large effects against the pathogen and can be observed in both seedling and adult plant stages. To date, 50 loci containing 78 resistant genes/alleles to PM [7,8] and 74 genes ( Yr1 – Yr74 ) to YR [9,10] have been identified in bread wheat and its relatives. This type of resistance has a strong tendency to be overcome by new races, particularly when a single gene is deployed over large areas.…”

Genetic analysis and molecular mapping of resistance to Puccinia striiformis f. sp. pseudo‐hordei in common wheat

“…A large translocation on chromosome 6AL from Thinopyrum ponticum (carrying the wheat stem rust resistance gene Sr26 ) contributed by the AvR parent explains the large linkage block on chromosome 6A in the T/A genetic map. The second translocation is the widely reported 5B:7B reciprocal translocation derived from the Teal parent, which was also identified in the genetic map of the T/A DH population (Dracatos et al ., ).…”

“…Selected linkage groups of the genetic map for the Teal × Avocet R wheat doubled haploid population (Dracatos et al ., ) showing the stable quantitative trait loci ( QTL ) identified in both phenotypic replicates (green and blue corresponding to replicates 1 and 2, respectively). The name on QTL bars has two components: the provisional name of the gene at the QTL and the logarithm of odds ( LOD ) value recorded for the QTL .…”

“…() identified major‐effect resistance QTLs on chromosomes 1HS and 7HL, derived from the barley genotypes WI2585 and Haruna Nijo, respectively. Currently, more than 74 loci conferring resistance to Pst have been designated ( Yr1–Yr74 ; Yr26 is considered to be synonymous with Yr24 ), predominately from common wheat but also from durum wheat and wild progenitors (Park, ; Dracatos et al ., ). A selection of the Australian wheat cultivar Avocet (Avocet R, AvR) carries complementary genes ( Yr73 and Yr74 ) for seedling resistance to Pst (Dracatos et al ., ).…”

Identification of Quantitative Resistance to Puccinia striiformis and Puccina triticinia in the Soft Red Winter Wheat Cultivar ‘Jamestown’

“…In 2000, 21 new races of stripe rust were identified in the United States, and among these new races, eight had combinations of virulence to resistance genes that were previously known to provide exceptional resistance in the United States (Chen et al, 2002). This new stripe rust population has increased adaptation and fitness yet contains many virulence alleles that are not required to overcome resistance in soft red winter wheat cultivars east of the Rocky Mountains (Chen, 2005;Dracatos et al, 2016). New races were identified that are able to germinate at warmer temperatures, allowing for disease development later in the season.…”