A detached leaf method for propagating Puccinia coronata races and assessing crown rust resistance in oat (Avena sativa L.)

Authors: Jackson, Eric; Obert, Donald; CHONG, JAMES - AG & AGRI FOOD, WINNIPEG; AVANT, JANA - FORMER USDA ARS ABERDEEN; Bonman, John

Submitted to: Plant Pathology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 6/1/2008
Publication Date: 10/1/2008
Citation: Jackson, E.W., Obert, D.E., Chong, J., Avant, J., Bonman, J.M. A detached leaf method for propagating Puccinia coronata races and assessing crown rust resistance in oat (Avena sativa L.). Plant Pathology 92:1400-1406

Interpretive Summary: Crown rust is the most devastating disease of oat. To combat the disease, producers rely on cultivars released by plant breeders with genetic resistance. One major obstacle in producing oat cultivars with lasting resistance is the ability to clearly understand the genes responsible. Recently, researchers from the United States Department of Agriculture-Agricultural Research Service in Aberdeen, ID have published findings that showed how precisely controlled experiments using specific isolates of the pathogen can improve studies aimed at understanding the crown rust resistance mechanisms. One challenge for this type of work is maintaining the specific isolates without contamination from other strains of the same pathogen. In addition, in typical screening experiments much space is required to study large plant populations. Therefore, the USDA-ARS scientists at Aberdeen, ID collaborated with a scientist from Agriculture & Agri-Food Canada, Winnipeg, MB, Canada to develop a method to generate and maintain the crown rust pathogen on detached oat leaves in the laboratory. Using the method, the scientists were able to produce spores and maintain uncontaminated isolates for important genetic tests. In addition, the method was used to identify oat lines with both simple and complex resistance using very little space. Overall, this work provides a key tool scientist need to study resistance mechanisms controlling crown rust, which should aid in efforts to develop new cultivars with resistance.

Technical Abstract: The crown rust pathogen Puccinia coronata is an obligate biotroph with wind disseminated propagules and numerous races. These characteristics make propagation of single-race cultures difficult. Additionally, genetic studies using single-races in field and greenhouse environments are also difficult because pure cultures can easily become contaminated. In this study we developed an isolated propagation system for P. coronata and tested the resulting system for its ability to assess host resistance. Ten centimeter oat leaf sections were harvested, disinfested, and suspended in sterile plastic boxes by enclosing 3.5 cm sections of each leaf end between 4% agar blocks amended with various chemical constituents. The exposed sections (approx. 4-cm) were inoculated with P. coronata urediniospores suspended in water. Boxes were sealed and incubated in a lighted growth cabinet until sporulation. Viable spores were produced on leaves in all treatments, while 6-benzylaminopurine (BAP) and Kinetin treatments sustained the leaves longer and yielded the most viable spores. Based on this data, the BAP treatment was adopted and used for additional studies. Detached leaves of 16 differential oat cultivars showed the same reactions as whole plants screened under standard conditions in a growth chamber. In addition, values for diseased leaf area and pustule density on detached leaves of eight oat lines from the USDA ARS Aberdeen breeding program were significantly correlated with measurements on intact plants. The proposed detached leaf system should be useful for the propagation of numerous single-race P. coronata cultures as well as evaluation of complete and partial host resistance under highly controlled conditions.