Location: Plant Science Research2008 Annual Report
1a. Objectives (from AD-416)
This project will address in oat, one of our important cereals, the needs for an understanding of the molecular/structural organization of its large complex genome, means to effectively identify and manipulate more durable race non-specific quantitative resistance to its major disease, crown rust, and the development of new biotic and abiotic stress resistance germplasm in elite agronomic backgrounds through the following objectives: Objective 1: Characterize the complex segmental homoeologous structure of allohexaploid cultivated oat through molecular marker analysis of monosomic and nullisomic chromosome-deficient stocks. Objective 2: Identify and map key genes (quantitative trait loci or QTLs) for important traits, particularly race non-specific crown rust resistance, by developing and phenotyping mapping populations and employing new molecular markers (EST-SSR and DArT). Objective 3: Develop cultivated oat germplasm with introduced biotic and abiotic stress resistance and high-value traits through introgressing crown rust resistance from wild oat species, exploring heat stress and disease resistance from genes introduced by crosses with corn, and evaluating high-value trait sources through coordination of regional spring oat nurseries.
1b. Approach (from AD-416)
Monosomic (single chromosome deficient) oat plants needed to complete a full series of 21 lines each deficient for a different oat chromosome will be identified cytologically and with molecular markers among derivatives of oat x corn crosses. Molecular marker linkage groups will be assigned to chromosome using these monosomic lines to develop a comprehensive genomic map for cultivated oat. The QTL identification of race non-specific (partial) crown rust in oat germplasm MN841801-1 will be enhanced with additional field and molecular marker data including the use of new DArT markers, and the effectiveness of marker-assisted selection will be tested for efficiency and effectiveness in transfer of the resistance QTLs into other oat backgrounds. New oat crown rust resistance genes will be introgressed into cultivated oat from wild oat species. Previously produced oat lines containing segments of corn chromosomes will be further developed and evaluated for possible enhanced heat tolerance and disease resistance. Coordination of cooperative regional spring oat performance nurseries will be used to identify optimal current oat genotypes for use as parents in crosses for introgressions and germplasm enhancement.
3. Progress Report
Participation in an international cooperative project to develop diversity array technology (DArT) molecular markers for oat produced approximately 2,700 potentially polymorphic DArT markers with 1,010 of these mapped on the Kanota x Ogle core genetic linkage map for oat. Toward being able to integrate the molecular marker linkage map with a physical chromosomal map in oat, DNA samples were extracted from oat cytogenetic stocks that are each deficient for a member of one pair of the 21 pairs of chromosomes of oat. These DNA samples were submitted to test if the DArT assay system can detect reduced dosage of markers located on the chromosome pair missing a member, and thus allow assignment of molecular marker linkage group to physical chromosome. Tetraploid wild oat species, Avena murphyi and Avena barbata, were evaluated as sources of new genes for resistance to crown rust of oat as all the known major resistance genes of hexaploid cultivated oat Avena sativa and later those introduced from hexaploid wild oat Avena sterilis have within a few years after development become ineffective due to virulence shifts in the rust population. Five accessions of tetraploid Avena murphyi were found to have resistance to current rust races; however, the resistance was inhibited or suppressed in all cases when these accessions were crossed to hexaploid cultivated oat. This suppression occurred even with the use of different cultivated oat lines, and the resistance could not be recovered among segregating progeny. In contrast, 3 lines tested of the 48 resistant accessions identified among a total of 359 Avena barbata accessions screened in collaborative efforts with the Cereal Disease Lab maintained their resistance when hybridized with cultivated oat. These selections show promise as useful new sources of crown rust resistance in oat improvement. Novel oat lines, produced earlier each with individual segments of corn chromosomes incorporated into them either as additions or as translocations onto oat chromosomes, were screened to identify ones with specific segments of corn chromosomes carrying genes for two key enzymes involved in C4-type photosynthesis. A line with a segment of chromosome 6 carried the gene for pyruvate orthophosphate dikinase (PPDK) and one with a segment of chromosome 9 the gene for phosphoenolpyruvate carboxylase (PEPc). These translocation lines, unlike simple alien chromosome addition lines, will transmit the corn segments through both the male and female gametes. Thus, the two translocation lines were crossed to produce progeny that would include ones disomic for the translocations and have two copies of each of these corn genes in attempts to transfer the C4 photosynthesis trait from corn to oat. (Relates to NP 301, Components 2 and 3, by providing new genetic information and materials.)
5. Significant Activities that Support Special Target Populations
Kowles, R.V., Walch, M.D., Minnerath, J.M., Bernacchi, C.J., Stec, A.O., Rines, H.W., Phillips, R.L. 2008. Expression of C4 photosynthetic enzymes in oat-maize chromosome addition lines. Maydica. 53:69-78.