Rhexocercosporidium matricariae sp. nov.: A New Pathogen on the Medicinal Plant Matricaria recutita

A new disease was observed on chamomile plants (Matricaria recutita) in various commercially cultivated fields in 2016 and 2017 in Germany. From symptomatic stems and leaves, the fungal species described here was isolated repeatedly. Kochʼs postulates using in planta experiments were fulfilled by inoculation of chamomile plants proving the fungus to be the causal agent of the disease. Morphological studies and phylogenetic analyses using internal transcribed spacer, large subunit, and translation elongation factor-1a sequences suggested that the fungus represents a new species within the genus Rhexocercosporidium (Helotiales). The data are presented together with a description of the growth parameters and comprehensive illustrations of the new species, Rhexocercosporidium matricariae. All species so far assigned to Rhexocercosporidium are compared and discussed. The combination Rhexocercosporidium microsporum is validated.