A fine line – endophytes or pathogens in Arabidopsis thaliana

Fungal endophytes were isolated in 2007 and 2008 from healthy Arabidopsis thaliana, growing in its natural environment in Braunschweig, Germany. In 2007, the predominant isolate was Leptosphaeria maculans. In 2008, the assemblages of isolates differed, with not even one isolate of L. maculans. Greater amounts of precipitation may explain the abundance of L. maculans in 2007, since its infection requires rainfall. In 2008, the main genera isolated were Phomopsis, Phoma and Coniothyrium. Following inoculation into axenically cultured A. thaliana on agar medium – conditions stressful for the host, but favorable for the endophytes – only three of eight isolates colonized asymptomatically: Plectosphaerella cucumerina and two Coniothyrium spp., emphasizing the delicate balance between fungal virulence and host defense. L. maculans, P. cucumerina and the Coniothyrium spp. could be used for investigating the molecular basis of interactions between A. thaliana and fungal endophytes that colonize A. thaliana in its natural environment.

► Endophytic fungi were isolated from Arabidopsis thaliana growing in its natural environment.
► In one year, Leptosphaeria maculans was the most common isolate.
► Inoculation of some of the endophytes into axenically cultured Arabidopsis thaliana led to disease.