Effect of volatile substances from Streptomyces philanthi RM-1-138 on growth of Rhizoctonia solani on rice leaf

Volatile compounds generated from Streptomyces philanthi RM-1-138 grown on autoclaved wheat seeds for seven or 14 days suppressed the growth of four plant pathogenic fungi (Rhizoctonia solani PTRRC-9, Pyricularia grisea PTRRC-18, Bipolaris oryzae PTRRC-36 and Fusarium fujikuroi PTRRC-16). The inhibition was most pronounced on R. solani PTRRC-9 while the least inhibition was against F. fujikuroi PTRRC-16. The volatile compounds from 14 days old cultures exhibited a stronger inhibitory effect (52.85-100 %) on the four fungal strains than those from the 7 days old cultures (17.03-89.40 %). Identification of the volatile organic compounds produced by Streptomyces philanthi RM-1-138 using gas chromatography-mass spectrometry (GC-MS) revealed 17 and 36 compounds from the seven days old and 14 days old cultures, respectively. They could be chemically grouped into alcohols, alkenes, aromatic hydrocarbons, sulfides, ketones, ester and alkanes, some of which were known antimicrobial agents. Among them, the most abundant volatile component was 3,7-dimethylocta-1,6-dien-3-ol (L-linalool). Effect of the inoculum size and spore concentration of S. philanthi RM-1-138 prepared as a wheat seed inoculum on the suppression of R. solani PTRRC-9 was studied. Total inhibition of growth (100 %) was achieved using an inoculum size of at least 15 g l(-1) and a spore concentration of 1 xs 10(7) spore ml(-1), respectively. Consistent (closed container) transfer of volatile substances from S. philanthi RM-1-138 to healthy tissues of rice leaves effectively reduced the incidence and/or the severity of sheath blight disease caused by mycelium or sclerotia. The cell wall of R. solani PTRRC-9 showed damage as observed by a scanning electron microscope (SEM) and a transmission electron microscope (TEM). The results indicated that the volatile compounds from S. philanthi RM-1-138 could effectively control the rice sheath blight disease caused by R. solani PTRRC-9.