Identification and validation of a common stem rust resistance locus in two bi-parental populations

Authors: RANDHAWA, MANDEEP - International Maize & Wheat Improvement Center (CIMMYT); SING, RAVI - International Maize & Wheat Improvement Center (CIMMYT); DREISIGACKER, SUSANNE - International Maize & Wheat Improvement Center (CIMMYT); BHAVANI, SRIDHAR - International Maize & Wheat Improvement Center (CIMMYT); HUERTA-ESPINO, JULIO - Instituto Nacional De Investigaciones Forestales Y Agropecuarias (INIFAP); Rouse, Matthew; NIRMALA, JAYAVEERAMUTHU - University Of Minnesota; SANDOVAL-SANCHEZ, MARICARMEN - International Maize & Wheat Improvement Center (CIMMYT)

Submitted to: Frontiers in Plant Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 11/16/2018
Publication Date: 11/30/2018
Citation: Randhawa, M.S., Sing, R.P., Dreisigacker, S., Bhavani, S., Huerta-Espino, J., Rouse, M.N., Nirmala, J., Sandoval-Sanchez, M. 2018. Identification and validation of a common stem rust resistance locus in two bi-parental populations. Frontiers in Plant Science. https://doi.org/10.3389/fpls.2018.01788.
DOI: https://doi.org/10.3389/fpls.2018.01788

Interpretive Summary: Wheat stem rust is a fungal disease of wheat that decreases yield. A strain of the wheat stem rust fungus known as Ug99 emerged in Uganda in 1999 and threatens global wheat production because it is able to infect nearly all wheat varieties. Wheat lines 'Huhwa' and 'Yaye' possess resistance to Ug99, but the genetics of resistance was unknown. We determined that each line has a single major resistance gene. We also determined that the resistance in both lines is likely the previously characterized gene Sr9h. We derived a molecular marker that could be used to facilitate the selection of Sr9h from Huhwa. The identification this resistance gene in these wheat lines and a linked molecular marker will facilitate the improvement of stem rust resistance in worldwide and United States wheat cultivars. Ug99 resistant wheat cultivars will protect global and United States wheat production from yield loss if a Ug99 epidemic were to occur in the United States.

Technical Abstract: Races belonging to Ug99 lineage of stem rust fungus Puccinia graminis f. sp. tritici (Pgt) continue to pose a threat to wheat (Triticum aestivum L.) production in various African countries. Growing resistant varieties is the most economical and environmentally friendly control measure. Recombinant inbred line (RIL) populations from the crosses of susceptible parent 'Cacuke' with the resistant parents 'Huhwa' and 'Yaye' were phenotyped for resistance at the seedling stage to Pgt race TTKSK (Ug99) and in adult plants in field trials at Njoro, Kenya for two seasons in 2016. Using the Affymetrix Axiom breeders SNP array, two stem rust resistance genes, temporarily designated as SrH and SrY, were identified and mapped on chromosome arm 2BL through selective genotyping and bulked segregant analysis (BSA), respectively. Kompetitive allele specific polymorphism (KASP) markers and simple sequence repeat (SSR) markers were used to saturate chromosome arm 2BL in both RIL populations. SrH mapped between markers cim109 and cim114 at a distance of 0.9 cM proximal, and cim117 at 2.9 cM distal. SrY was flanked by markers cim109 and cim116 at 0.8 cM proximal, and IWB45932 at 1.9 cM distal. Two Ug99-effective stem rust resistance genes derived from bread wheat, Sr9h and Sr28, have been reported on chromosome arm 2BL. Infection types and map position in Huhwa and Yaye indicated that Sr28 was absent in both the parents. However, susceptible reactions produced by resistant lines from both populations against Sr9h-virulent race TTKSF+ confirmed the presence of a common resistance locus Sr9h in both lines. Test of allelism is required to establish genetic relationships between genes identified in present study and Sr9h. Marker cim117 linked to SrH was validated and can to be used for marker assisted selection for this gene, however a combination of phenotypic and genotypic assays is desirable for both genes especially for selection of Sr9h in breeding programs.