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 genotyped on set of wheat lines with Huhwa in the pedigree and is advised 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.
Highlights
Stem rust, caused by Puccinia graminis f. sp. tritici (Pgt), is one of the most damaging fungal diseases of bread and durum wheat (Triticum aestivum L. and Triticum turgidum ssp. durum, (Desf.) Husnot., respectively) (Roelfs et al, 1992)
This study identified a common stem rust resistance locus located on chromosome arm 2BL in wheat cultivars Huhwa and Yaye
A robust SNP marker cim117 closely linked to SrH was identified and validated on advanced wheat lines carrying Huhwa in their pedigree
Summary
Stem rust, caused by Puccinia graminis f. sp. tritici (Pgt), is one of the most damaging fungal diseases of bread and durum wheat (Triticum aestivum L. and Triticum turgidum ssp. durum, (Desf.) Husnot., respectively) (Roelfs et al, 1992). Durum, (Desf.) Husnot., respectively) (Roelfs et al, 1992). It can cause complete yield losses under severe epidemics if susceptible cultivars are grown in rust hot-spot areas (Saari and Prescott, 1985; Dean et al, 2012). Global wheat production was threatened by stem rust when a highly virulent Pgt race known as Ug99 or TTKSK that combined virulence to Sr31 and various other commonly deployed resistance genes was detected in 1998 in Uganda (Pretorius et al, 2000; Jin et al, 2007, 2008). The new variants belonging to Ug99 race group and their geographical spread have further reduced the number of effective genes that can be used by breeding programs
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