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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

2013 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:

Development and characterization of chromosome addition and introgression lines for new resistance genes from existing 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 screened with race TMLKC. The seven resistant BC2F1 plants were backcrossed with CS and approximately 150 BC3F1 seeds were obtained. For the Zhong 4-derived backcross population, 139 BC1 seeds of the cross LMPG6/Zhong 4//LMPG6 were produced. This population will be screened this fall for stem rust resistance to initiate selection of a disomic addition line carrying the stem rust resistance gene from Zhong 4.

Introgression of a new Sr gene from Langdon/Ae. speltoides PI369581 amphidiploid into durum wheat. One resistant BC1F1 plant having 29 chromosomes was previously identified from backcrossing a Langdon/Ae. speltoides PI369581 amphidiploid with durum line Rusty. Twelve BC1F2 plants with a high level of resistance to TMLKC were recovered from 90 BC1F2 seeds derived from the resistant BC1F1 plants. These plants have been crossed with the Rusty 5D(5B) disomic substitution line and 321 hybrid seeds have been produced.

Introgression and characterization of a new Sr gene from wheat-Th. intermedium disomic addition line Z5. Previous study showed that Z5 carries one pair of translocation chromosomes in which a Th. intermedium chromosome segment was located at the distal region of the long arm. Z5 was previously backcrossed to the CS Ph1 inhibitor. From 169 BC1F1 plants tested with race TMLKC, three plants with 42 chromosomes were identified. Eight resistant BC2F2 plants carrying a pair of homozygous translocation chromosome were identified by evaluating 163 BC2F2 plants derived from one of the three BC1F1 plants with resistance to TMLKC.

Introgression of the Ug99-effective Sr genes from wheat-Th. intermedium addition line TAI27. TAI27 was previously crossed to the CS Ph1 inhibitor, and then backcrossed to CS. All BC1 plants were susceptible to stem rust, indicating that either the gene in TAI27 is recessive, that inheritance is complex, or that a different race of stem rust is needed to differentiate the gene. Additional stem rust races and F2 progeny will be studied to determine how to most efficiently detect the gene.


Last Modified: 12/24/2014
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