Bioherbicidal activity and host range of Teratoramularia rumicicola strain TR4 isolated from Rumex crispus in Japan

Rumex species, including R. crispus , R. obtusifolius , and R. japonicus , are problematic weeds that reduce forage production and hinder effective land use in Japanese pasture systems. This study aimed to identify a bioherbicide candidate that selectively targets Rumex weeds while remaining safe for forage crops. To this end, we isolated a fungal pathogen from a naturally infected R. crispus leaf collected in Japan and conducted morphological and molecular identification and host range evaluations. The isolate, designated TR4, was identified as Teratoramularia rumicicola based on its morphological characteristics and phylogenetic analysis of concatenated internal transcribed spacer (ITS) and large subunit (LSU) rDNA sequences. Host range studies revealed that TR4 caused visible symptoms and significantly reduced shoot biomass in all three Rumex species, while no disease symptoms were observed in any of the five forage crops tested. This study reports T. rumicicola for the first time in Japan, extending its known distribution beyond South Korea. The host specificity and liquid culture compatibility of TR4 suggest its potential as a locally adapted microbial herbicide for selective Rumex control in pasture systems.