Mapping and validation of all-stage resistance to stem rust in four South African winter wheat cultivars

Authors: CHEMONGES, MARTIN - University Of The Free State; HERSELMAN, LIEZEL - University Of The Free State; PRETORIUS, ZACHARIAS - University Of The Free State; Rouse, Matthew; MARE, ANSORI - University Of The Free State; BOSHOFF, WILLEM - University Of The Free State

Submitted to: Euphytica
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 7/5/2022
Publication Date: 12/20/2022
Citation: Chemonges, M., Herselman, L., Pretorius, Z.A., Rouse, M.N., Mare, A., Boshoff, W.H. 2022. Mapping and validation of all-stage resistance to stem rust in four South African winter wheat cultivars. Euphytica. 219. Article 11. https://doi.org/10.1007/s10681-022-03143-4.
DOI: https://doi.org/10.1007/s10681-022-03143-4

Interpretive Summary: Wheat is grown on over 37 million acres in the United States. The rust diseases of wheat can cause devastating yield losses. Emerging strains of the wheat stem rust pathogen such as Ug99 threaten global and United States wheat production. In order to mitigate wheat stem rust, disease-resistant wheat varieties need to be developed. Several South African winter wheat cultivars have been observed to express all-stage resistance to the Ug99 race group. To study the inheritance of resistance, the cultivars Komati, Koonap, Limpopo and SST 387 were crossed with the stem rust susceptible wheat Line 37-07. Segregation of resistance to a Ug99 derivative in each of the four populations indicated the presence of a single dominant resistance gene. The resistance gene mapped to the short arm of chromosome 6D and linked molecular markers were identified. Our data suggested the presence of Ug99-effective stem rust resistance gene SrTmp in all four wheat cultivars. The resistance wheat lines characterized as possessing a Ug99-effective stem rust resistance gene and the molecular markers identified as linked to this gene can be used in wheat breeding to develop Ug99-resistant wheat varieties for the United States.

Technical Abstract: Several South African winter wheat cultivars have been observed to express all-stage resistance to local races of Puccinia graminis f. sp. tritici (Pgt). To study the inheritance of resistance, the cultivars Komati, Koonap, Limpopo and SST 387 were crossed with the stem rust susceptible wheat Line 37-07. Segregation of resistance to Pgt race PTKST in each of the four F2 populations indicated the presence of a single dominant resistance gene. Allelism tests conducted among these parents revealed resistant F2 progeny only, suggesting that either the same gene, alleles of the same gene, or closely linked genes confer resistance in these cultivars. The resistance gene mapped to the short arm of chromosome 6D and was flanked by simple sequence repeat (SSR) markers psp3200, wms4528, barc183 and wms4862. The four cultivars tested negative using single nucleotide polymorphism (SNP) markers linked to Sr42, SrTmp and SrCad located on chromosome 6DS. Allelism tests between the resistant cultivars and Norin 40 (Sr42) and CnsSrTmp (SrTmp) were inconclusive as only resistant F2 progeny were obtained. This suggested that either an unknown allele of the same gene confers resistance to Pgt race PTKST in these cultivars or that Sr42 or SrTmp may indeed be involved. Multi-race phenotyping results ruled out the involvement of Sr42 or SrCad, but suggested the presence of SrTmp in all four wheat cultivars. This research has provided evidence that the genetic base of stem rust resistance in a number of South African winter wheat cultivars is monogenic. SNP markers BS00085937 and SSR markers psp3200 and wms4862 linked to the mapped gene(s) were 90.9-92.7% effective in predicting stem rust phenotypes among 55 South African breeding lines and cultivars and can be useful for marker-assisted selection.