Characteristics of leaf rust fungi of temperate cereals and their host relationships

Abstract

This thesis describes work carried out mainly on the uredinial stage of the leaf rust fungi of temperate cereals, comprising the brown rusts of barley, rye and wheat as well as oat crown rust and the wheat and barley yellow rusts.

The taxonomic position of these pathogens was investigated in colony growth studies carried out under controlled conditions, with an emphasis on characters which were independant of cereal host factors. A clear morphological distinction could be made between oat crown rust, wheat brown rust, barley brown rust, rye brown rust and the yellow rusts of wheat and barley. However, no distinction apart from the host range could be made between wheat and barley yellow rust.

In culture experiments the isolates were tested for their ability to grow on detached leaves of their host plants, and some of the isolates were used in axenic culture studies. All the isolates showed identical virulence patterns on detached leaves as on whole host plants. None of the isolates tested could be maintained in axenic culture.

Cytogenetical characteristics were studied in some of the rust isolates. The dikaryotic binucleate condition prevailed in all isolates up to the stage of stomatal penetration. Attempts to obtain hybridisation between different races of wheat yellow rust failed.

Quantitative aspects of colony growth and development were investigated in a series of studies in controlled conditions.Differences in response to inoculum density were observed in experiments with barley brown rust and yellow rust and were related to the different patterns of epidemic development of these two species. The colony growth patterns of the cereal leaf rusts in host and non-host relationships showed strong host preference. However, unexpected colony development occurred in some of the pathogen/non-host combinations.