Homoeologous recombination-based transfer and molecular cytogenetic mapping of a wheat streak mosaic virus and Triticum mosaic virus resistance gene Wsm3 from Thinopyrum intermedium to wheat.

KEY MESSAGE: Here, we report the production of a wheat- Thinopyrum intermedium recombinant stock conferring resistance to wheat streak mosaic virus and Triticum mosaic virus. Wheat streak mosaic caused by the wheat streak mosaic virus (WSMV) is an important disease of bread wheat (Triticum aestivum) worldwide. To date, only three genes conferring resistance to WSMV have been named and two, Wsm1 and Wsm3, were derived from the distantly related wild relative Thinopyrum intermedium. Wsm3 is only available in the form of a compensating wheat-Th. intermedium whole-arm Robertsonian translocation T7BS·7S#3L. Whole-arm alien transfers usually suffer from linkage drag, which prevents their use in cultivar improvement. Here, we report ph1b-induced homoeologous recombination to shorten the Th. intermedium segment and recover a recombinant chromosome consisting of the short arm of wheat chromosome 7B, part of the long arm of 7B, and the distal 43% of the long arm derived from the Th. intermedium chromosome arm 7S#3L. The recombinant chromosome T7BS·7BL-7S#3L confers resistance to WSMV at 18 and 24 °C and also confers resistance to Triticum mosaic virus, but only at 18 °C. Wsm3 is the only gene conferring resistance to WSMV at a high temperature level of 24 °C. We also developed a user-friendly molecular marker that will allow to monitor the transfer of Wsm3 in breeding programs. Wsm3 is presently being transferred to adapted hard red winter wheat cultivars and can be used directly in wheat improvement.