Project Number: 5442-21000-033-24
Project Type: Reimbursable

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

Objective:
The objectives of this project are to: 1) transfer new genes for resistance to stem rust Ug99 races from four Thinopyrum species (Th. junceum, Th. bessarabicum, Th. intermedium, and Th. ponticum) and Aegilops caudata into wheat and 2) develop doubled haploid (DH) or recombinant inbred (RI) populations for mapping novel sources of resistance to Ug99 in tetraploid wheat.

Approach:
A recent evaluation showed that four wheat-alien species addition lines Z6 (wheat-Th. intermedium), W5336 (wheat-Th. bessarabicum), HD3505 (wheat-Th. junceum), and AII (Alcedo/Ae. caudata) as well as 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 the four addition lines into wheat, we will utilize Chinese Spring (CS) monosomics or Ph1 inhibitor to induce primary translocations between wheat chromosomes and their alien homoeologs carrying the resistance genes. The four addition lines will be crossed with CS monosomics or Ph1 inhibitor. About 500 F2 plants from each of the crosses will be tested with stem rust. The resistant plants will be analyzed using molecular markers and fluorescent genomic in situ hybridization (GISH) to identify the plants with translocations. After primary 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 primary translocations developed above. At least 50 BC1 plants will be evaluated with stem rust 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. For development of DH or RI populations in tetraploid wheat, five Ug99-resistant tetraploid wheat accessions, including T. carthlicum PI 387696, T. dicoccoides PI 466979, T. dicoccum PI 193883, T. polonicum CItr 14803, and T. turgidum PI 387336, will be crossed to Rusty, a durum wheat (T. durum) line that is a near universally susceptible to stem rust. The F1 hybrids from these crosses will be used to develop DH or RI populations. At least 200 DH or RI lines will be developed from each of the crosses using wheat-maize hybridization or single seed descent, respectively.