Diversity of wheat phyllosphere fungi in different agricultural production systems

Fusarium head blight (FHB) is a disease affecting cereals world-wide caused by Fusarium fungi. The disease is of great economic importance especially since it is associated with contamination by harmful mycotoxins produced by Fusarium spp. In recent years, several studies have reported lower mycotoxin contamination of organically produced cereals compared with those produced conventionally. An unexplored factor is differences in the microbial communities on cereal crops between the organic and conventional systems, which may exert a biocontrol effect on FHB. The aim of this thesis was to investigate the effect of different environmental and agricultural factors on Fusarium communities and fungal phyllosphere communities in wheat in different agricultural production systems. New primers for amplifying Fusarium communities, in conjunction with 454 se-quencing, were evaluated, and Fusarium communities associated with soil and wheat kernels were successfully characterised. Comparison of fungicide-treated and untreated wheat leaves from 18 fields in Sweden in 2011 revealed that fungicide use was associ-ated with decreased evenness of fungal communities. Furthermore, organic farming was associated with increased fungal species richness on wheat leaves when pairs of 22 organically and conventionally managed fields in Sweden were compared in 2012. There was no difference in the abundance of leaf pathogens between cropping systems. Several fungal species were consistently found regardless of geographical location, year and cropping system, while fungal abundance was highly variable between fields. Both Fusarium and fungal communities were affected by agricultural intensity. How-ever, there was no difference in Fusarium community composition in wheat kernels from organically and conventionally managed fields. The method evaluated in this thesis can be used to monitor Fusarium communities in the field, which is important in order to develop strategies for limiting FHB and mycotoxin contamination. The present thesis demonstrates that fungicide use and organic farming are associated with differen-tial fungal communities in the wheat phyllosphere. This indicates that there is an oppor-tunity for the farmer to manage these communities with the aim of enhancing their biocontrol potential against plant pathogens such as Fusarium