Einfluss von Landschaftsstruktur und landwirtschaftlicher Nutzung auf das Auftreten blattpathogener Pilze an Weizen und die genetische Diversität von Mycosphaerella graminicola (Anamorph Septoria tritici)

Abstract

This study was part of the interdisciplinary Project BIOPLEX on the evaluation of biodiversity of organisms in different agricultural landscapes. The investigations aimed at determining the influence of different landscape structures in the regions around Goettingen and Giessen on the epidemic of fungal plant pathogens such as Septoria tritici, Septoria nodorum, Blumeria graminis f. sp. tritici, Drechslera tritici-repentis, Puccinia striiformis and Puccinia recondita. Additionally, aggressiveness and genetic diversity of Septoria tritici depending on landscape diversity was analysed.Results from the field showed a generally wider spectrum of leaf pathogenic fungi in the region around Giessen than in the region of Goettingen. Furthermore, the diversity of pathogen species in complex structured landscapes was higher and the disease severity lower than in less structured landscapes. In both years Septoria tritici was the most dominant pathogen on each investigated field. The landscape effect on the epidemiology of S. tritici must be considered as marginal, although there seemed to be a relation between landscape diversity and disease severity of this fungus. Nevertheless, the intensity of cropping practices was considerably more important in the region around Goettingen than in the region around Giessen. This is due to the fact that most farmers around Giessen consider agriculture as a sideline job. Therefore, the differences evaluated in this study result rather from different cropping intensities than from different landscape structures.Variability in aggressiveness of Septoria tritici isolates within site-specific populations was high. However, a direct influence of landscape diversity on the aggressiveness of S. tritici isolates was not found. Genetic analysis of Septoria tritici populations revealed 79 different genotypes among 290 tested isolates, representing 73 percent of all possible genotypes out of 108 possible combinations of the three or four alleles of the three applied markers. Furthermore, more than 2/3 of the total genetic variability of S. tritici was found within one field population or even within one square metre. These results lead to the conclusion that the investigated fungal populations did not evolve due to different landscape structures. Septoria tritici appears to exist as highly mixed worldwide population which is represented on any spot.