Genome-wide association mapping for seedling and adult plant resistance to stripe rust in synthetic hexaploid wheat.

Habtemariam Zegeye,Ayele Badebo,Awais Rasheed,Farid Makdis,Francis C Ogbonnaya,David D Fang

doi:10.1371/journal.pone.0105593

Abstract

Use of genetic diversity from related wild and domesticated species has made a significant contribution to improving wheat productivity. Synthetic hexaploid wheats (SHWs) exhibit natural genetic variation for resistance and/or tolerance to biotic and abiotic stresses. Stripe rust caused by (Puccinia striiformis f. sp. tritici; Pst), is an important disease of wheat worldwide. To characterise loci conferring resistance to stripe rust in SHWs, we conducted a genome-wide association study (GWAS) with a panel of 181 SHWs using the wheat 9K SNP iSelect array. The SHWs were evaluated for their response to the prevailing races of Pst at the seedling and adult plant stages, the latter in replicated field trials at two sites in Ethiopia in 2011. About 28% of the SHWs exhibited immunity at the seedling stage while 56% and 83% were resistant to Pst at the adult plant stage at Meraro and Arsi Robe, respectively. A total of 27 SNPs in nine genomic regions (1BS, 2AS, 2BL, 3BL, 3DL, 5A, 5BL, 6DS and 7A) were linked with resistance to Pst at the seedling stage, while 38 SNPs on 18 genomic regions were associated with resistance at the adult plant stage. Six genomic regions were commonly detected at both locations using a mixed linear model corrected for population structure, kinship relatedness and adjusted for false discovery rate (FDR). The loci on chromosome regions 1AS, 3DL, 6DS and 7AL appeared to be novel QTL; our results confirm that resynthesized wheat involving its progenitor species is a rich source of new stripe (yellow) rust resistance that may be useful in choosing SHWs and incorporating diverse yellow rust (YR) resistance loci into locally adapted wheat cultivars.

Highlights

Stripe rust (YR), caused by Puccinia striiformis tritici (Pst), is a major threat to wheat production in many areas
In 2010, the breakdown in resistance conferred by Yr27 and the absence of resistant cultivars in Ethiopia led to an expenditure of more than US$3.2 million on fungicides, and over 400 000 ha of wheat were estimated to have been infected by yellow rust (YR) [1]
The higher disease severity observed at Meraro compared to Arsi Robe may be attributed to environmental effects that affect the incidence and level of disease expressions at different locations

Summary

Introduction

Stripe (yellow) rust (YR), caused by Puccinia striiformis tritici (Pst), is a major threat to wheat production in many areas. A recent experience is the stripe rust of near - epidemic proportions in the Central West Asia and North Africa (CWANA) and SubSaharan Africa regions in 2010 [1]. Previous YR epidemics have occurred in some major wheat producing regions including China, Europe, Australia, Ethiopia, South Africa, the US and South Asia [2]. In 2010, the breakdown in resistance conferred by Yr27 and the absence of resistant cultivars in Ethiopia led to an expenditure of more than US$3.2 million on fungicides, and over 400 000 ha of wheat were estimated to have been infected by YR [1]. Despite the concerted efforts to control the disease using fungicides, substantial losses were prevalent on highly susceptible cultivars in areas with high disease pressure. Breeding resistant cultivars is the most economical and environmentally best approach to reduce the use of fungicides and to reduce crop losses due to this disease

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