Conidia production of Exserohilum rostratum, a biocontrol agent against red sprangletop, by a two-phase system using sponge matrix

Bioherbicides have been developed as biological agents to offer non-chemical alternatives to reduce chemical discharge into the environment and are applied in a similar manner to chemical herbicides to control noxious weeds. The most common microorganism used as the active ingredient is a plant pathogenic fungus and its propagules are conidia or mycelial fragments. The fungal isolate MKY3010, Exserohilum rostratum (a synonym of Setospharia rostrata in telemorph , showing potential efficacy as a bioherbicide against red sprangletop (Leptochloa chinensis were obtained in Kyushu, Japan. However, this fungus did not produce any conidia in liquid culture. Mycelia of E. rostratum grew well in sponge matrix submerged in liquid culture (the first phase . Consequently conidia were abundantly produced from the mycelia when the sponge matrix was exposed to the air (the second phase . This two-phase system consistently produced over 5 x 10 8 conidia L -1 within 5 days. In addition, the conidia obtained were more uniform in size and achieved higher percentages of germination and appressoria formation compared with those produced on agar media. These results showed that a two-phase system using sponge matrix could be a promising tool for providing the conidia of E. rostratum to develop a bioherbicide against red sprangletop, an emerging weed in agro-ecosystem.