Location: Hard Winter Wheat Genetics Research2010 Annual Report
1a. Objectives (from AD-416)
Objective 1: Develop adapted hard red or white wheat germplasm lines with improved resistance to emerging or intractable problems in wheat production and marketing. Objective 2: Increase understanding of the molecular basis of parasite virulence, host resistance, and stress tolerance for these problems. Objective 3: Develop and apply phenotypic and genotypic selection technology for these traits to hard red or white winter wheat germplasm or cultivar development.
1b. Approach (from AD-416)
Production of high quality hard red or white winter wheat is limited by recurring intractable problems such as leaf rust, Fusarium head blight, Hessian fly, and heat stress during the grain filling period. In addition, new emerging problems such as stripe rust, stem rust, and Karnal bunt threaten the production or marketing of high quality grain. The first objective of this project is to develop adapted hard red or white wheat germplasm lines with improved resistance or tolerance to these problems. We will utilize existing sources and identify new sources of resistance, introgress them into desirable backgrounds, and then release them for use as parents of commercial cultivars. The second objective is to increase our understanding of the molecular basis of parasite virulence, host resistance, and stress tolerance to support strategic development and deployment of genetic resistance. Greater understanding of secreted virulence/avirulence effectors in the Hessian fly and the leaf rust pathogen may lead to better strategies for durability. Greater understanding of the mechanisms of durable rust resistance and heat tolerance may lead to discovery of new genes or alleles with complementary mechanisms and to optimized gene combinations in new cultivars. The third objective is to develop and apply phenotypic and genotypic selection technology for these traits to hard red or white winter wheat germplasm and cultivar development. This is an essential component of the technology transfer effort. Large-scale phenotypic screening data for Hessian fly and Karnal bunt resistance and genotypic marker data will be provided to cooperators.
3. Progress Report
In 2010, we analyzed 10,000 wheat breeding samples from 5 public breeding programs and 3 private breeding programs for molecular markers. All of the samples were screened with either simple sequence repeat (SSR) or single nucleotide polymorphism (SNP) markers as requested by breeders and the data were sent to breeders in time for selection. We also analyzed two regional nurseries with 30 published markers linked to important traits of interest to breeders. The data have been sent to wheat researchers in the hard winter wheat (HWW) region. We assembled an association mapping population with 213 US hard and soft wheat breeding lines and cultivars. This population has been genotyped with 250 SSR markers. This population has been evaluated for aluminum tolerance in acidic soils in Enid, OK and for root aluminum ion uptake in a lab experiment. The results indicated that some lines showed good resistance in acid soils, but were susceptible in lab tests. Two F7 recombinant inbred line (RIL) populations from the crosses between two Chinese landraces, Haiyanzhong and Huangfangzhu, and Wheaton (a highly susceptible parent) were evaluated for Fusarium head blight (FHB) resistance. The data were analyzed and quantitative trait locus (QTL) analysis showed that Haiyanzhong has a major QTL on chromosome 7D and it explained about 22-30% of phenotypic variation for percentage of scabbed spikes. In Huangfangzhu, two QTL with major effects on percentage of scabbed spikes were mapped on chromosome 3BS (location of Fhb1) and 7AL. The manuscripts for the mapping work are in preparation. About 109 backcross progenies with resistance gene Fhb1 in a Wesley background were tested in the field at Manhattan KS. The lines containing Fhb1 showed low FHB severity after inoculation. In another marker-assisted selection (MAS) project, Fhb1 and several other FHB resistance QTLs were transferred into hard winter wheat Jagger (KS), Overland (NE) and Overley (KS). About 200 backcrosses were made between marker-assisted selected plants and recurrent parents. A system has been developed using biolistics to test the function of genes from the leaf rust pathogen, P. triticina, as candidates for avirulence factors. The technique involves using the gene gun and co-bombarding two plasmids into the wheat seedlings. One plasmid contains the reporter gene and the other contains the avirulence gene candidate. The plasmids are shot into seedling leaf tissue of wheat isolines that contain different resistance genes. The level of expression of the reporter gene is measured. A reduction of the reporter gene expression is correlated with the induction of the hypersensitive disease resistance response. A positive reaction indicates that the gene may function as an avirulence factor in the host/parasite interaction. A wheat stripe rust screening nursery was established at Rossville, KS in 2009/2010. It included three mapping populations, three regional performance nurseries, and 160-240 entries from each of eleven wheat breeding programs. A stem rust screening nursery was established at Manhattan, KS in 2009/2010.
1. Development of an improved version of the H21 wheat resistance gene for Hessian fly. Hessian fly is a serious pest of wheat and the use of resistance genes is the most effective and cost efficient means of control. H21 is one of the few resistance genes that is still highly effective against Hessian fly populations in the field. However, the usefulness of H21 in wheat breeding is limited due to unfavorable agronomic traits associated with the rye chromosomal arm that contains H21. ARS scientists working with research collaborators at Kansas State University (KSU) have identified resistant wheat lines with shortened rye chromosomal segments that reduce or eliminate undesirable agronomic traits associated with the rye chromosome. Wheat lines containing the improved version of H21 are being used by wheat breeders to improve resistance to Hessian fly.
2. Analysis of genes expressed in the gut tissue of Hessian fly could lead to a better understanding of resistance mechanisms in wheat. Hessian fly is a serious pest of wheat and a model for the study of gall midge/plant interactions. The insect pest is controlled mainly through deploying resistant wheat varieties. However, the resistance in host plants is often short-lived, lasting for only 6-8 years for a specific resistance gene before the fly overcomes it. This research systematically analyzed the genes expressed in the gut tissue of Hessian fly larvae. This research provided a foundation for further research on the function of individual fly genes and for identification of potentially useful targets for novel control strategies using genetic engineering.
3. Reactive oxygen molecules correlate with resistance to Hessian fly. Host plant resistance is the most effective and cost efficient means to control Hessian fly, a serious pest of wheat. However, the rapid development of new biotypes has made resistance in host plants short-lived. A better understanding of plant resistance mechanisms is needed to develop more durable resistant wheat. This research investigated the potential role of reactive oxygen species (ROS) in plant defense against Hessian fly. ARS scientists and research collaborators from KSU found that hydrogen peroxide, a major form of ROS, accumulated to high levels at the feeding site in resistant wheat and in non-host rice plants following Hessian fly attack. Hydrogen peroxide was very toxic to fruit fly larvae, a related insect that belongs to the same order as Hessian fly. This research broadened our understanding of plant defense against different herbivores and provided a foundation for future research that may lead to more effective host plant resistance.
4. Mapping of leaf rust resistance gene Lr12. Leaf rust is the most important disease of wheat worldwide. Wheat leaf rust resistance gene Lr12 is effective in adult plants, but not in seedlings. However, this gene can be effective in seedlings when the complementary gene Lr27 is also present. Our long term goal is to understand how Lr27 increases the effectiveness of Lr12. ARS and KSU scientists at Manhattan, KS determined the chromosome location of Lr12 and identified molecular markers that flank the gene. These will be useful for further fine mapping studies that could eventually lead to isolating the gene.
5. Mapping genes that affect quality of wheat. Wheat quality factors are important in determining the suitability of wheat for end-use products and economic value, and they are major targets for marker-assisted breeding. Progeny from a cross between the Chinese hard red wheat Ning7840 and the US soft red winter wheat Clark were evaluated for quality traits including grain protein content (GPC), test weight (TW), kernel weight (KW), and kernel diameter (KD), and hardness index (HI) at three Oklahoma locations from 2001 to 2003. A genetic map was constructed to identify quantitative trait loci (QTLs) responsible for these traits. Eight QTLs for TW, seven for KW, six for KD, two each for GPC and the HI measured by near-infrared reflectance (NIR) spectroscopy, and four for the HI measured by the single kernel characterization system. A QTL for HI was located at the Pinb-D1 gene for hardness on chromosome 5DS. This research identified numerous loci that affect grain quality and marker-assisted selection has potential for improving wheat quality.
6. Identification of a new resistance gene for Fusarium head blight. Wheat cultivar Sumai 3 is one of the best resistance sources for Fusarium head blight (FHB). Its resistance was reported to be derived from each of its parents. However, the resistance gene from one of its parents, Funo, has never been identified. A new resistance gene on chromosome 7A of Sumai 3 was identified which explains 22% of phenotypic variation for resistance. Molecular genetic analysis revealed that the gene originated from Funo, thus solving an old mystery. This gene and the associated molecular markers will be useful in breeding for FHB resistance.
7. Adapted hard winter wheat parental lines with new stem rust resistance genes were distributed to wheat breeders. Ug99 and related strains are African races of wheat stem rust that are virulent on most wheat varieties in the US and elsewhere. To increase resistance to African races of stem rust, five new stem rust resistance genes (Sr22, Sr32, Sr35, Sr39, Sr40) were introduced into five commercial wheat cultivars. These lines are being used by wheat breeders to develop elite new cultivars with resistance to Ug99.
8. New diagnostic test for Wheat Streak Mosaic Virus and Triticum Mosaic Virus. Wheat streak mosaic virus (WSMV) and Triticum mosaic virus (TriMV) are widespread throughout the southwestern Great Plains states. Both viruses have similar symptoms which makes visual identification almost impossible. ELISA methods for detection of the viruses in plant samples can be insensitive to low concentrations and depend on having high quality antiserum. Polymerase chain reaction (PCR) methods can be more sensitive and do not depend on antiserum. In both cases, only one of the viruses can be tested for per assay. ARS scientists and university collaborators developed a new multiplex method to test for both viruses at the same time in the same assay. Our new method has higher sensitivity and can be used to more rapidly and more accurately diagnose these viruses.
Sood, S., Kuraparthy, V., Bai, G., Gill, B.S. 2009. The Major Threshability Genes Soft Glume (sog) and Tenacious Glume (Tg), of Diploid and Polyploid Wheat, Trace Their Origin to Independent Mutations at Non-Orthogous Loci. Theoretical and Applied Genetics. 119:341-351