Introgression of chromosome segments from multiple alien species in wheat breeding lines with wheat streak mosaic virus resistance.

N Ali,Js Pat Heslop-Harrison,T Schwarzacher,R A Graybosch,H Ahmad,G L Hein

doi:10.1038/hdy.2016.36

Abstract

Pyramiding of alien-derived Wheat streak mosaic virus (WSMV) resistance and resistance enhancing genes in wheat is a cost-effective and environmentally safe strategy for disease control. PCR-based markers and cytogenetic analysis with genomic in situ hybridisation were applied to identify alien chromatin in four genetically diverse populations of wheat (Triticum aestivum) lines incorporating chromosome segments from Thinopyrum intermedium and Secale cereale (rye). Out of 20 experimental lines, 10 carried Th. intermedium chromatin as T4DL*4Ai#2S translocations, while, unexpectedly, 7 lines were positive for alien chromatin (Th. intermedium or rye) on chromosome 1B. The newly described rye 1RS chromatin, transmitted from early in the pedigree, was associated with enhanced WSMV resistance. Under field conditions, the 1RS chromatin alone showed some resistance, while together with the Th. intermedium 4Ai#2S offered superior resistance to that demonstrated by the known resistant cultivar Mace. Most alien wheat lines carry whole chromosome arms, and it is notable that these lines showed intra-arm recombination within the 1BS arm. The translocation breakpoints between 1BS and alien chromatin fell in three categories: (i) at or near to the centromere, (ii) intercalary between markers UL-Thin5 and Xgwm1130 and (iii) towards the telomere between Xgwm0911 and Xbarc194. Labelled genomic Th. intermedium DNA hybridised to the rye 1RS chromatin under high stringency conditions, indicating the presence of shared tandem repeats among the cereals. The novel small alien fragments may explain the difficulty in developing well-adapted lines carrying Wsm1 despite improved tolerance to the virus. The results will facilitate directed chromosome engineering producing agronomically desirable WSMV-resistant germplasm.

Highlights

Wheat streak mosaic virus (WSMV), transmitted by the wheat curl mite (WCM) Aceria tosichella Kiefer, is an important yield-limiting disease of wheat (Triticum aestivum, 2n = 6x = 42, AABBDD) (Graybosch et al, 2009)
Some transgenic wheat lines have been developed with WSMV resistance in controlled environments (Fahim et al, 2010), but have not been tested in the field
Some of the initial lines carrying Wsm1 were associated with undesirable traits such as reduced yield and poor bread-making quality, but subsequent crosses and selection eliminated many negative effects from the introgressed Th. intermedium chromatin (Divis et al, 2006; Graybosch et al, 2009)

Summary

Introduction

Wheat streak mosaic virus (WSMV), transmitted by the wheat curl mite (WCM) Aceria tosichella Kiefer, is an important yield-limiting disease of wheat (Triticum aestivum, 2n = 6x = 42, AABBDD) (Graybosch et al, 2009). Infected plants show greenish yellow streaks and chlorosis with stunted growth, low root biomass, reduced water uptake efficiency and low yield (Thomas et al, 2004; Price et al, 2010). Both WSMV and the mite vector survive during the late summer on 'green bridges' provided by volunteer wheat and other susceptible wild and cultivated grasses (Divis et al, 2006). As viral diseases cannot be controlled directly by agrochemicals, management of insect vectors and agronomic conditions must be used. Some transgenic wheat lines have been developed with WSMV resistance in controlled environments (Fahim et al, 2010), but have not been tested in the field

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Conclusion