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United States Department of Agriculture

Agricultural Research Service

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Location: Cereal Crops Research

2013 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. Four populations derived from crosses of durum Rusty with T. carthlicum PI 387696, T. dicoccum PI 193883, T. dicoccoides PI 466979, and T. turgidum PI 387336 have been advanced to F5:6 generations in 2013. Because the hybrid from the cross Rusty/T. polonicum CItr 14803 was highly sterile, we crossed CItr 14803 to durum wheat line 47-1 and durum cultivar Divide. The new hybrid will be used to develop RI populations. Molecular and cytogenetic manipulations of new sources of resistance genes derived from Thinopyrum and Aegilops species. Two wheat-Thinopyrum species partial amphiploids, Xiaoyan 784 and Zhong 4, were previously backcrossed to CS and LMPG6, respectively. From the backcross Xiaoyan 784/2*CS, seven resistant BC2F1 plants with 45 chromosomes were identified from 191 BC2F1 plants, and they were further backcrossed with CS to produce approximately 150 BC3F1 seeds. One resistant BC1F1 plant having 29 chromosomes was previously identified from backcrossing the Langdon/Ae. speltoides PI369581 amphidiploid with Rusty. Twelve resistant BC1F2 plants were recovered from 90 BC1F2 seeds derived from the resistant BC1F1 plants. Wheat-Th. junceum addition line HD3505 and two Alcedo/Ae. caudata addition lines, AII(C) and AIII(D), were characterized using DNA markers and GISH. HD3505 was identified to carry a pair of Th. junceum group 4 chromosomes and AII(C) and AIII(D) carry a pair of Ae. caudata chromosomes, 5C and 6C, respectively. They were crossed to CS monosomics 4D, 5A, and 6B, respectively. Three Robertsonian translocations have been identified among F2 plants from Mono 4D/HD3505, Mono 5A/AII(C), and Mono 6B/AIII(D) based on stem rust testing and GISH analysis. The three Robertsonian translocation lines have been backcrossed to the CS ph1b mutant to further reduce the alien chromatin. Introgression and characterization of Sr genes from wheat-Th. intermedium disomic addition lines Z5, Z6, and Tai 27. Previous studies showed that Z5 carries a pair of translocation chromosomes in which a Th. intermedium chromosome segment is located at the distal region of the long arm. Z5 was previously backcrossed to the CS Ph1 inhibitor. Eight resistant BC2F2 plants (2n = 42) carrying a pair of homozygous translocation chromosomes were identified from 163 BC2F2 plants. For the Zhong 5-derived line Z6, a stem rust gene was located to a short alien translocation on 1BS. However, stem rust reactions, molecular analysis, and GISH analysis indicated that the short alien translocation was actually the 1BS/1RS translocation carrying Sr31. The Th. intermedium alien addition line Tai27 has been crossed to the Chinese Spring Ph1 inhibitor and an F2 population produced for screening with stem rust.

4. Accomplishments

Last Modified: 06/27/2017
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