Suppression of rice sheath blight disease using a heat stable culture filtrate from Streptomyces philanthi RM-1-138

•Streptomyces philanthi inhibited the growth of seven phytopathogenic fungi.•Inhibitory culture filtrates of S. philanthi were mostly heat stable.•The autoclaved culture filtrate also inhibited Rhizoctonia solani.•Autoclaved culture filtrates suppressed rice sheath blight disease in greenhouse experiments.

Streptomyces philanthi RM-1-138, isolated from the rhizosphere soil of chili pepper in southern Thailand, was investigated for its antagonistic activity against phytopathogenic fungi. In dual culture on glucose yeast-malt extract (GYM) agar plates, this strain suppressed the mycelial growth of all seven plant pathogenic fungi tested (Rhizoctonia solani PTRRC-9, Pyricularia grisea PTRRC-18, Colletotrichum gloeosporioides NBCRSR-3, Colletotrichum capcisi NBCRSR-15, Ganoderma boninense NBCRSR-26, Fusarium fujikuroi PTRRC-16 and Bipolaris oryzae PTRRC-36) with an 82.2–89.2% inhibition and that was most pronounced on R. solani PTRRC-9. Heat treatment of the culture filtrate from growing R. solani PTRRC-9 at 40 °C, 60 °C, 80 °C, and 100 °C for 30 min and 121 °C for 15 min had no negative effect on the inhibitory activity against R. solani PTRRC-9 tested on both solid and liquid culture. The effective dose (>80% inhibition) of culture filtrate in liquid culture was at 5.0% (v/v) while it was at 10% (v/v) on the solid medium. This effectiveness was similar to those of the four chemical fungicides tested. The effect of S. philanthi RM-1-138 against R. solani PTRRC-9 was investigated using SEM and TEM. The compounds produced by S. philanthi RM-1-138 induced alterations to the cell-wall structure of R. solani PTRRC-9, that resulted in the loss of cytoplasm materials by partial lysis. The greenhouse experiment revealed that using either the culture filtrate or the autoclaved culture filtrate from S. philanthi RM-1-138 effectively suppressed rice sheath blight disease by up to 65.6 and 60.8%, respectively.

Graphical abstractEffect of culture filtrate of Streptomyces philanthi RM-1-138 on destruction of Rhizoctonia solani PTRRC-9 (that caused rice sheath blight disease) was observed under SEM and TEM. The control showed normal growth of R. solani PTRRC-9 (A) and the damaged R. solani PTRRC-9 after treated with culture filtrate of S. philanthi RM-1-138 (B).Figure optionsDownload full-size imageDownload as PowerPoint slide