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United States Department of Agriculture

Agricultural Research Service

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Location: Cereal Crops Research

2012 Annual Report

1a. Objectives (from AD-416):
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.

1b. Approach (from AD-416):
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.

3. Progress Report:
Development of five new DH and/or RI populations for mapping novel sources of resistance in tetraploid wheats. The F1 hybrids from crosses of durum Rusty with T. carthlicum PI 387696, T. dicoccum PI 193883, T. dicoccoides PI 466979, T. polonicum CItr 14803, and T. turgidum PI 387336 were previously produced. The F1 plants of three hybrids (Rusty/ PI 387696, Rusty/CItr 14803, and Rusty/PI 387336) were initially used to develop DH populations using wheat-maize hybridization. However, DH population development was unsuccessful due to the low frequency of hybrid embryo formation. Thus, the F1 plants of the hybrids were used to produce F2 seed, which are being used to develop RI populations. Approximately 1,200 F2 individuals (~300 plants/hybrids) have been grown to produce F3 seed for four of the hybrids except for Rusty/CItr 14803 hybrid, which was highly sterile. Development and characterization of chromosome addition and introgression lines for new resistance genes from existing Thinopyrum species partial amphiploids. The BC1 population from backcrossing Xiaoyan 784 with CS has been developed and selection of the monosomic additions with stem rust resistance will be conducted in the coming season. Zhong 4 has been crossed to LMPG6, and BC1population will be produced in the coming season. In addition, a BC1 population from backcrossing Langdon/Ae. speltoides PI369581 with Rusty was developed as a backup for this work and 157 BC1 plants were tested with race TMLKC. One resistant BC1 plants having 29 chromosomes have been identified and crossed to Rusty 5D(5B) substitution lines. Molecular-cytogenetic manipulation of new sources of resistance gene derived from Thinopyrum and Aegilops species. New Sr genes were initially planned to be transferred from four wheat-alien species disomic addition line Z6, AII (C), HD3505, and W5336 to wheat genome. As a backup for this work, the Sr genes from wheat-Th. intermedium addition lines Z5 and TAI27 and Alcedo/Ae. caudata disomic addition lines AIII (D) are also being transferring. The initial crosses between Ph1 inhibitor or monosomics and the seven addition lines have been made. The F2 populations from crosses of HD3505 with Ph1 inhibitor were tested with stem rust and 38, 90, and 711 plants with resistant, intermediate, and susceptible reactions, respectively, were obseved. The hybrids of Z5, Z6, and TAI27 with Ph1 inhibitor were also backcrossed to CS or Ph1 inhibitor and about 200 BC1 plants from each backcross were tested with stem rust. Selection of the resistant BC1 plants with 42 chromosomes is currently underway. So far, 10 resistant plants (2n = 42) carrying the translocation chromosome with the short-telomeric Th. intermedium chromatin have been identified based on GISH analysis.

4. Accomplishments

Last Modified: 06/28/2017
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