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United States Department of Agriculture

Agricultural Research Service

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Research Project: Introgression of New Stem Rust Resistance Genes from Thinopyrum Species into Wheat

Location: Cereal Crops Research

2012 Annual Report

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

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

3.Progress Report:

For developing chromosome addition lines with new Sr genes from existing wheat-Thinopyrum species partial amphiploids, Xiaoyan 784 (wheat-Th. ponticum) and Zhong 4 (wheat-Th. intermedium) have been crossed to CS and LMPG6, respectively. The BC1 population from backcrossing Xiaoyan 784 (wheat-Th. ponticum) with CS has been developed and selection of the monosomic additions with stem rust resistance will be conducted in the coming season.

New Sr genes were originally planned to be transferred from wheat-Th. intermedium disomic addition line Z5 and wheat-Th.bessarabicum chromosome 7J disomic addition line W5336 to wheat genome. Line Z5 was characterized by GISH and determined to carry one pair of translocation chromosome in which a Th. intermedium chromosome segment was located at the distal region of the long arm. Line Z5 was crossed to the CS Ph1 inhibitor, and then backcrossed to CS Ph1 inhibitor and CS, respectively. The 169 BC1 plants were tested with stem rust race TMLKC and segregation of 75 susceptible and 94 resistant plants was observed. Selection and characterization of the resistant plants with 42 chromosomes are currently underway.

The CS/Th. bessarabicum//Genaro 7J disomic addition line W5336 was crossed to CS monosomics for chromosomes 7A, 7B and 7D for developing Robertsonian translocations. W5336 and its wheat parent Genaro have been evaluated for reactions to seven local stem rust races (TMLKC, TPMKC, TPPKC, QFCSC, QTHJC, QCCJB, and MCCFC). Because we didn’t find any local races that can differentiate W5336 from Genaro, we discontinued further work on the Th. bessarabicum 7J addition line. As a backup for this project, we initiated the introgression of the Ug99-effective Sr genes from the wheat-Th. intermedium addition line TAI27 and one Langdon-Ae. speltoides (LDN/PI369581) amphidiploid. TAI27 was crossed to the CS Ph inhibitor, and then backcrossed to CS. The Langdon-Ae. speltoides amphidiploid was crossed and backcrossed with the durum Rusty and 157 BC1 plants were tested with race TMLKC. One resistant BC1 plant having 29 chromosomes derived from Langdon/PI 369581 has been identified and crossed to the Rusty 5D(5B) substitution line.

Last Modified: 4/24/2014
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