1a. Objectives (from AD-416)
Investigate the genetic mechanisms by which the plant hormones abscisic acid (ABA) and gibberellin (GA) control pre-harvest sprouting stand establishment, and drought and cold tolerance in wheat and model organisms. Develop and utilize molecular markers for the western region wheat and barley breeding programs for resistance to stem rust, other biotic and abiotic stresses, and end-use quality. Develop wheat cultivars with durable resistance to stripe rust, stem rust, soilborne diseases, cold and drought, and improved end-use quality for Western Region cropping systems using wheat germplasm resources from the USDA-ARS National Small Grains Germplasm Collection (NSGC) and other national and international sources.
1b. Approach (from AD-416)
Determine whether ABA sensitivity controls grain dormancy and tolerance to preharvest sprouting. Determine whether degree of drought tolerance and cold tolerance tend to correlate with each other and depend upon ABA sensitivity. Determine how GA signaling controls seed dormancy and plant height. Identify and use new and existing molecular markers linked to genes for biotic stress resistance, specifically for stripe rust resistance. Identify and use new molecular markers for genes linked to abiotic and end-user quality. Establish and use high-throughput molecular marker analysis systems to track the segregation of important genes in wheat and barley breeding programs. Characterize core wheat germplasm sets for use in identifying haplotypes important in Western Regional germplasm adaptation. Use molecular markers to link genotypes to phenotypes while maintaining critical haplotypes for enhancement, disease resistance and end-use quality in Western Region wheat breeding programs. Identify new sources of genes giving superior end-use quality, disease resistance, and resistance to cold and drought. FY09 Program increase. Add 0.00 SY.
3. Progress Report
Objective 1A addresses whether the plant hormone ABA controls wheat grain dormancy and preharvest sprouting tolerance. ABA hypersensitive mutants in wheat with both white and red kernels showed increased dormancy and required more time to break dormancy when dry. This phenotype correlated with decreased sprouting in the first year of testing. Objective 1B examined whether ABA controls wheat resistance to drought and cold stress. Preliminary tests failed to detect increased cold tolerance in ABA hypersensitive wheat. However, ABA hypersensitive mutants Warm3 and Warm4 show less water loss through leaf transpiration in drying soil suggesting increased drought tolerance. Objective 1C examines how the hormone GA controls seed germination and plant height. The DELLA gene RGL2 was identified as a key gene blocking seed germination. GA stimulates germination via DELLA destruction mainly by F-box gene SLY1, but another gene SNE can also serve this function. DELLA can also be deactivated by GA receptor GID1 without destruction. Objective 2A. Identify and use molecular markers for biotic stress resistance, abiotic stress and end-use quality. Most MAS work submitted to the lab from CA, ID, MT, OR, and WA scored for disease resistance; 62% were for rust resistance. Traits scored include: disease resistance to Fusarium Head Blight, Hessian Fly, Septoria Tritici Blotch, and Strawbreaker Foot Rot; baking quality traits include glutenins, grain protein, hardness; and agronomic genes controlling flowering, plant height, and drought tolerance. The genotyping lab generated 4 genetic maps; Stem Rust, Vernalization, Strawbreaker Foot Rot and agronomic performance. Objective 2.B. 352,068 datapoints were scored in order to use molecular marker analysis systems to track the segregation of important genes in breeding programs. Objective 2.C. To characterize core wheat germplasm for use in identifying haplotypes important in Western Regional germplasm, the lab coordinated the PNW SNP project. 1536 PNW lines will be genotyped with 9,000 SNP per line this year. Objective 3 is to develop wheat germplasm and cultivars adapted to Western Region cropping systems with durable resistance to stripe rust, soilborne disease, cold and drought, and with improved end-use quality. Cara club wheat released in 2007 was made available to growers in 2009. Club wheat ARS970164-3C was identified for breeder seed increase based on stripe rust and soil borne disease resistance, increased yield, and improved grain quality and grading characteristics. This new cultivar will reduce production risk and improve quality. Recurrent selection populations for resistance to the soilborne diseases Fusarium crown rot and lesion nematodes were derived from crosses to diverse international germplasm. The number and location of Fusarium crown rot resistance loci were identified in Sunco. Molecular markers increase the efficiency of trait analysis by pre-selecting lines with favorable alleles for re-test. Lines with resistance to eyespot, barley yellow dwarf virus, preharvest sprouting and Hessian fly were selected by assaying molecular markers. Cold tolerance was assayed on two mapping populations.
1. The hormone ABA triggers wheat grain dormancy. Wheat varieties sometimes lack seed dormancy leading to a tendency for mature grain to germinate on the mother plant before harvest. This preharvest sprouting causes financial hardship for farmers because the grain must be used for feed. ARS Scientists in Pullman, WA, developed a technique to identify ABA hypersensitive mutations in wheat resulting in increased grain dormancy which should provide increased resistance to preharvest sprouting. The increase in ABA-hormone response caused grain to lose dormancy more slowly after maturity, but did not eliminate the capacity to lose dormancy by after-ripening. This research provides knowledge and new wheat lines (Warm1 and Warm4) that can be used to breed for resistance to preharvest sprouting.
2. Identification of stripe rust resistance loci in the Kansas wheat cultivar, Jagger. It is unknown what gene or genes were conditioning resistance to stripe rust in wheat line Jagger, which has remained resistant to major races of stripe rust from its release until 2009. ARS Scientists in Pullman, WA, in collaboration with researchers in OK, KS, and China, used analysis of Quantitative Trait loci in a Jagger by OK2174 mapping population that was planted and evaluated for reaction to stripe rust at Pullman and Central Ferry WA, in KS, and in China and genotyped in OK. The results indicated that the major gene for resistance in Jagger is on chromosome 2AS and is likely the gene YR17 derived from VPM or an allele and that a second locus on chromosome 5 was also responsible for resistance in China. This research provides molecular markers to select for the Jagger stripe rust resistance and provides epidemiological data that is critical to strategies for maintaining durable resistance to new races of stripe rust that overcome Yr17 in the United States.
3. Development of new wheat cultivars with resistance to multiple diseases that will enhance the quality of the wheat export crop. The problem was that the current club wheat cultivar Bruehl, which occupies the most acreage in WA, does not possess resistance to eyespot and does not reliably grade club in the grain grading sector. ARS Researchers in Pullman, WA, used marker assisted selection for resistance to eyespot and stripe rust, combined with greenhouse and field based evaluation for disease resistance and grain production traits, as well as laboratory based quality analysis to develop a new wheat breeding line which will be proposed for release this year. ARS970163-4C soft white club wheat will undergo initial seed increase in the fall of 2010. This line meets the highest quality standards for the western soft wheat and club wheat crop, is agronomically competitive with current wheat cultivars, and requires no fungicide for disease control.
4. DELLA destruction stimulates seed germination and growth. It is unknown how the hormone GA controls seed germination and stem elongation. Research conducted by ARS Scientists in Pullman, WA, showed that GA can stimulate plant growth and seed germination by destroying DELLA repressors of plant growth and seed germination. This destruction occurs mainly through action of the gene SLEEPY1 and to a lesser extent a similar gene called SNEEZY. This research provides new gene targets for control of plant height and seed germination which will be used in strategies to prevent preharvest sprouting and to obtain good seedling emergence and stand establishment in wheat.
Schramm, E.C., Abellera, J.C., Strader, L., Garland Campbell, K.A., Steber, C.M. 2010. Isolation of ABA-responsive mutants in allohexaploid bread wheat (Triticum aestivum L.): Drawing connections to grain dormancy, preharvest sprouting, and drought tolerance. Plant Science. 179:620-629.