Abstract:

Wheat (Triticum aestivum L.) leaf rust, caused by Puccinia triticina (formerly P. recondita f. sp. tritici), is one of the most destructive diseases on wheat production throughout the world. The use of resistant varieties is an economical, efficient and environmental-friendly way for minimizing the losses caused by wheat leaf rust. To date, about 90 leaf rust resistance genes have been found or identified in wheat and its relatives. The resistance gene Lr24, derived from Thinopyrum ponticum (2n = 70), confers very strong resistance to wheat leaf rust. Eight molecular markers of Lr24 have been developed, however more markers are needed for identifying and mapping the gene. In the present study, Xcwem17 was discovered as a new EST-SSR marker of Lr24 with the susceptible line Thatcher and 468 individuals of F₂ progeny derived from a cross between TcLr24 and Thatcher. The wheat seedlings of parents and F₂ generation were inoculated solely with leaf rust spores, and cultured in greenhouse at (20±5)℃. The infection types (IT) of all plant materials were scored in six grades with Roelfs’s system at the 14th day after inoculation. Twenty-two pairs of SSR and EST-SSR primer on wheat chromosome 3D were used to tag the resistance gene Lr24. One of the four polymorphism primers co-segregated with Lr24 was acquired after testing with 468 F₂ individuals. Sequence analysis showed that Xcwem17 was 223 bp, in which from the 7th to 220th bp (coding 71 amino acid residues) showed 36% identity to a poly-protein gene of rice chromosome 5. The marker Xcwem17 was further converted into a STS marker, and tested together with a reported SCAR marker in the same population. The results showed that they both co-segregated with Lr24, and could amplify a single 310-bp (SCAR marker) or 180-bp (STS marker) band only in TcLr24 and Taishan 1 (a landrace carried Lr24). It suggests that the STS marker developed in the study can be used in MAS directly.

Key words:

Puccinia triticina, Resistance gene, Lr24, Marker-assisted selection