Location: Forage Seed and Cereal Research2013 Annual Report
1a. Objectives (from AD-416):
Objective 1. Discover and test germplasm that has genetic resistance to principal or emerging diseases in forage seed and wheat production. Subobjective 1.A. Develop an approach for evaluation of orchardgrass germplasm for resistance to choke disease. Subobjective 1.B. Identify germplasm of Lolium with resistance to rust diseases. Subobjective 1.C. Identify germplasm and increase seed for wheat and barley lines with resistance to stem rust Ug99. Subobjective 1.D. Identify genomic sequences in Brachypodium associated with non-host resistance to the wheat stem rust pathogen. Objective 2. Develop plant disease modeling tools to protect food supply and implement biosecurity strategies against rusts and other diseases of grass and wheat. Subobjective 2.A. Develop a model for timing of application of fungicides for control of ergot in Kentucky bluegrass. Subobjective 2.B. Determine the role of aphids in infection of orchardgrass by Epichloe typhina. Subobjective 2.C. Implement weather-based epidemiological model for stem rust of perennial ryegrass. Subobjective 2.D. Adapt ryegrass stem rust models to wheat stem rust.
1b. Approach (from AD-416):
Genetic resistance to stem rust will be investigated in cereal crops by selection, breeding and field evaluations, and in grasses by genetic mapping, quantitative trait loci analysis and transcriptome analysis. Molecular markers for stem rust resistance in Lolium will be chosen and validated. Genetic sequences associated with initial response of Brachypodium to the stem rust pathogen will be determined. Greenhouse and field experiments will be used to detect genetic resistance to the choke pathogen in grasses, and to determine whether aphids play a role in the infection process for this pathogen. An epidemic model for stem rust in grasses will be validated and expanded to include overwintering phenomena, and the grass stem rust model will be applied to wheat stem rust by experimental determination of critical parameters in greenhouse and field tests. Field experiments will be used to create a predictive model for infection by the ergot pathogen.
3. Progress Report:
Research to discover and test disease-resistant germplasm for grasses has been initiated with orchardgrass choke disease, for which a seedling inoculation method has been developed, and with stem rust, for which research on several grass crop species is in progress. In perennial ryegrass, rust-resistant selections have been crossed with susceptible turf-type lines and the progeny have been tested and selected for the next breeding cycle; some resulting materials have been shared (through an MTA) with a major university breeding program. Collaborative work with barley has produced candidates for Ug99-resistant lines adapted to Western and Northwest US production. Rust resistance reactions in the genomic model grass Brachypodium were characterized at the microscopic and molecular level, and genomic data on a useful genotype of this grass was shared with a larger ARS Brachypodium genomics project. In epidemiological research, methods were established for examining the importance of aphids in the infection process for orchardgrass choke. The epidemiological model for a ryegrass stem rust decision support aid was tested with data from 5 different years. Key biological processes to be incorporated into a wheat stem rust model were quantified in experiments with wheat.
1. Stem rust in the model grass Brachypodium. Stem rust is of ongoing concern in grasses, and represents a renewed threat to wheat and barley with the emergence of UG99 and related novel pathogen strains. Fundamental understanding of genetic resistance genetics and mechanisms is needed to protect the US grain crop, but is difficult to attain in wheat and many grasses due to their genetic complexity. We characterized response of the model grass Brachypodium to the wheat stem rust pathogen and to other slightly more compatible stem rust strains. Researchers in Corvallis, Oregon, documented through microscopy the time course of very early infection events, and produced the first collection of genetic messages produced by the plant at the critical early phase of the host-pathogen interaction. Decoding these messages will produce essential time-course information for stem rust resistance research, and provide extensive data for hypothesis generation and testing about early events in wheat stem rust resistance.
2. E. typhina infection biology. Epichloë typhina is an important fungal pathogen responsible for significant yield loss in orchardgrass (Dactylis glomerata L.) seed production fields. Although infections are presumed to occur through leaves and stems, details of the infection process and conditions that favor leaf infection are not well understood. Researchers in Corvallis, Oregon, determined that spore germination and growth are optimal at warm temperatures and prevented by temperatures below 41F or above 95F. They discovered that spores can survive periods of dry weather with little loss of viability, and that leaf wounds created mechanically or by an insect can stimulate growth of the pathogen within and across leaf surfaces. These results will be helpful in devising disease control strategies, as they indicate that the optimal time for fungicide control may be just after seed harvest, when leaf wounds, temperatures, and abundant spores are optimal for infection.
3. Wheat stem rust epidemiology. Wheat stem rust is a very destructive disease that has been held in check by host genetic resistance, but such defense is threatened by the emergence of new virulent strains of the pathogen. Information is now urgently needed about the dynamics of epidemic development so that other management procedures can be used effectively until new resistance is found. The speed of an epidemic depends critically on the length of time between infection and the production of the next generation of spores (the latent period). Researchers in Corvallis, Oregon, developed a mathematical equation to predict the duration of the latent period for wheat stem rust based on ambient temperature. This equation will be used in predicting epidemic development, and as a benchmark to assess the epidemiological of new, virulent strains of stem rust.
Figueroa, M., Alderman, S.C., Garvin, D.F., Pfender, W.F. 2013. Infection of Brachypodium distachyon by formae speciales of Puccinia graminis: early infection events and host-pathogen incompatibility. PLoS One. 8(2):e56857.