A Combination of Leaf Rust Resistance Genes, Including Lr34 and Lr46, Is the Key to the Durable Resistance of the Canadian Wheat Cultivar, Carberry

Abstract

The hexaploid spring wheat cultivar, Carberry, was registered in Canada in 2009, and has since been grown over an extensive area on the Canadian Prairies. Carberry has maintained a very high level of leaf rust (Puccinia triticina Eriks.) resistance since its release. To understand the genetic basis of Carberry’s leaf rust resistance, Carberry was crossed with the susceptible cultivar, Thatcher, and a doubled haploid (DH) population of 297 lines was generated. The DH population was evaluated for leaf rust in seven field environments at the adult plant stage. Seedling and adult plant resistance (APR) to multiple virulence phenotypes of P. triticina was evaluated on the parents and the progeny population in controlled greenhouse studies. The population was genotyped with the wheat 90 K iSelect single nucleotide polymorphism (SNP) array, and quantitative trait loci (QTL) analysis was performed. The analysis using field leaf rust response indicated that Carberry contributed nine QTL located on chromosomes 1B, 2B (2 loci), 2D, 4A, 4B, 5A, 5B, and 7D. The QTL located on 1B, 2B, 5B, and 7D chromosomes were observed in two or more environments, whereas the remainder were detected in single environments. The resistance on 1B, detected in five environments, was attributed to Lr46 and on 7D, detected in seven environments to Lr34. The first 2B QTL corresponded with the adult plant gene, Lr13, while the second QTL corresponded with Lr16. The seedling analysis showed that Carberry carries Lr2a, Lr16, and Lr23. Five epistatic effects were identified in the population, with synergistic interactions being observed for Lr34 with Lr46, Lr16, and Lr2a. The durable rust resistance of Carberry is attributed to Lr34 and Lr46 in combination with these other resistance genes, because the resistance has remained effective even though the P. triticina population has evolved virulent to Lr2a, Lr13, Lr16, and Lr23.

Interactions Between Lr67 or Lr34 and Other Leaf Rust Resistance Genes in Wheat (Triticum aestivum)

“…Both Lr34 and Lr67 interacted with Lr16 to produce an enhanced resistance, even though lines with Lr16 alone were not significantly different from susceptible lines. This may reflect on the ability of Lr16 to interact with other resistance genes, as it has been shown previously to do with genes like Lr13 ( Samborski and Dyck, 1982 ) and both Lr34 and Lr46 in Carberry ( Bokore et al, 2022 ).…”

“…Lr34 appears to be key to its high level of resistance, as progeny lines derived from Pasqua with the four other resistance gene were fairly susceptible ( McCallum and Thomas, 2014 ). Similarly, the high level of durable resistance in the cultivar Carberry is conditioned by the combination of Lr2a , Lr16 , Lr23 , Lr13 , Lr34 , and Lr46 ( Bokore et al, 2022 ), in which the key is the interaction of Lr34 and Lr46 with the other resistance genes. These multi-pest resistance genes along with others, such as Sr2 , appear to function very well in combinations with other genes to condition effective and durable resistance, often by boosting the effect of other resistance genes ( Ellis et al, 2014 ).…”

“…They represent a range of effectiveness from mostly ineffective ( Lr13 ) to highly effective ( Lr32 ). Both Lr13 and Lr16 are in many Canadian wheat cultivars, such as Carberry ( Bokore et al, 2022 ), because popular wheat cultivars grown in the recent past like AC Barrie and AC Domain have either or both genes and donated these genes to the current generation of wheat cultivars. Lr13 is relatively ineffective against the Canadian population of P. triticina , as nearly all isolates are virulent to Lr13 ( McCallum et al, 2021 ).…”

“…However, it may still have an effect on reducing leaf rust severity in combination with other genes, such as Lr34 and Lr67 . Complete virulence to Lr16 is rare in Canada ( McCallum et al, 2021 ) but nearly all isolates have an intermediate level of virulence and combinations of Lr16 with genes, such as Lr34 and Lr46 , are fairly effective at reducing leaf rust severity ( Bokore et al, 2022 ). In contrast, Lr32 is a very effective leaf rust resistance gene in Canada with no virulence detected to date ( McCallum et al, 2021 ); however, it has not yet been deployed in any Canadian wheat cultivars.…”

Identification of Disease Resistance Parents and Genome-Wide Association Mapping of Resistance in Spring Wheat

“…As reviewed by Lagudah et al [ 52 ], the region that harbors Lr34 also coincides with several other disease resistance genes, including stripe rust ( Yr18 ), powdery mildew ( Pm38 ), leaf tip necrosis ( Ltn1 ), and barley yellow dwarf virus ( Bdv1 ) genes. Since the Lr34 gene has been reported to interact with other resistance genes to increase the level of resistance [ 53 , 54 , 55 , 56 ], it has been extensively introgressed in the Canadian wheat cultivars [ 57 , 58 ]. It should, however, be noted that the exact position of the Lr34 gene on chromosome 7D differs by ~1.5 Mb depending on the version of the physical maps (7D:47412062-47424490 in RefSeq v1.0 versus 7D:48955909-48955803 in RefSeq v2.0).…”