Project Number: 5442-21000-033-23
Project Type: Specific Cooperative Agreement

Start Date: Mar 01, 2011
End Date: Jan 31, 2016

Objective:
The objective of this cooperative research project is to transfer new genes for resistance to Ug99 from three Thinopyrum species (Th. bessarabicum, Th. intermedium, and Th. ponticum) into wheat.

Approach:
Thinopyrum species are excellent sources of genes for stem rust resistance. A recent evaluation showed that two disomic addition (2n=44) lines W5336 (wheat-Th. bessarabicum) and Z5 (wheat-Th. intermedium) and two partial amphiploids (2n=56) Zhong 4 (wheat-Th. intermedium) and Xiaoyan 784 (wheat-Th. ponticum) showed immunity or a high level of resistance to stem rust Ug99 races. To transfer the resistance genes from W5336 and Z5 into the wheat genome, we will utilize monosomics to induce primary translocations between wheat chromosomes and their homoeologs carrying the resistance genes. W5336 is a Chinese Spring (CS)/Th.bessarabicum//Genaro 7J addition line and it will be crossed with CS monosomic for chromosomes 7A. About 300-400 F2 plants from the cross will be tested with stem rust. The resistant plants will be analyzed using molecular markers to identify the plants with putative translocations. Fluorescent genomic in situ hybridization (GISH) will be further used to confirm compensating centromeric translocations (Robertsonian). The homoeologous group of the alien chromosome in Z5 has not been determined, thus CS Ph1 inhibitor will be used to induce primary translocations from Z5 using the similar procedure described above. After compensating translocations are identified, a second round of chromosome engineering using ph1b-induced homoeologous recombination will further reduce the size of the alien chromosome segment. The CS ph1bph1b plants will be crossed and backcrossed to the Robertsonian translocations developed above. At least 50 BC1 plants will be evaluated with stem rust test and analyzed with the molecular markers used to detect Ph1. The resistant BC1 plants that are homozygous for ph1b and heterozygous for the translocated alien segment will be backcrossed to CS. About 1000 to 2000 crossed seeds should be produced. These hybrids will be tested with stem rust. The resistant hybrid plants will be tested with 8-10 molecular markers for the chromosome of interest. After identifying lines with reduced alien segments, each line will be examined by GISH to determine the size of the alien segment. To transfer the resistance genes from the partial amphiploids Zhong 4 and Xiaoyan 784 to wheat, we will initially develop chromosome addition lines in a CS background. Zhong 4 and Xiaoyan 784 will be crossed and backcrossed with CS. The BC1 plants will be tested with stem rust. The resistant plants will be cytologically studied for identification of plants with 2n = 43 chromosomes. The plants with 2n = 43 will be self-pollinated and their progenies will be cytologically examined for selection of disomic addition lines (2n = 44). The disomic addition lines will be tested with the multiple races. The chromosome addition lines developed in this work will be used for further introgression of the genes for stem rust resistance through chromosome engineering described above.