Interactions between fungal plant pathogens on leaves. Especially simultaneous development of Rhynchosporium secalis and Drechslera teres on barley

Summary in the original language of the document

Disease causing fungi are a major potential threat to yield in both organic and conventional cereal production, and generally several different species of pathogenic fungi are found together on the same plants in the field. This PhD thesis concludes that interaction between different fungal species may influence total disease levels and often via negative effects, such that less disease is observed where several diseases occur together relative where they are found individually.
Such potential interaction effects have often been ignored in the past, as plant diseases have traditionally been studied as single independent events. The thesis provides an important review of available literature on the subject; which considers the theoretical background for analysing foliar disease interactions as well as previously published data on disease interactions. Difficulties in distinguishing different types of interaction, mainly different types of competition are emphasized. In a specific study, the thesis considers the barley diseases scald (caused by Rhynchosporium secalis) and net blotch (caused by Drechslera teres).
Aiming to understand how diseases interact in the field, it is further concluded that increased focus should be placed on considering the dynamics of the plant growth along with the epidemiological development. This is pointed out by observations of antagonism between scald and net blotch on individual leaves and further via a simulation model. The model shows that differences in pathogen dispersal rates between vertical leaf layers of the plant and the overlap of leaf layers over time are important for competitive outcome from two fungal competitors.
Detailed disease observations on individual leaves provide insight into understanding interplay between disease severity and plant senescence. This level of detail does not, though, give a better description of yield loss from disease, relative to the generally used plot assessment, where disease severities are determined as averages over the crop.
The work presented in the PhD thesis is relevant for all who work with foliar pathogens. Optimal disease control and plant breeding is based on knowledge of factors determining epidemic development and hence interactions between simultaneously developing pathogens must be considered