Suppression of Magnaporthe oryzae by culture filtrates of Streptomyces globisporus JK-1

An isolate, JK-1, was obtained as a contaminant from a fungal culture, and identified as Streptomyces globisporus. In dual cultures on solid media, this strain suppressed mycelial growth of numerous plant pathogenic fungi, especially that of Magnaporthe oryzae, Bipolaris maydis and Cryphonectria parasitica. Culture filtrates of JK-1 inhibited mycelial growth of M. oryzae, and histological investigations showed that conidial germination and appressorial formation of M. oryzae were suppressed on detached rice leaves. When applied at 15 mu l per 5-cm-long detached leaf, washed cells of JK-1 at 10(8) CFU/ml could suppress disease incidence of rice blast caused by M. oryzae co-inoculated at 5 x 10(5) spores/ml, but disease incidence was not reduced when washed cells of JK-1 were used at 10(6) or 10(7) CFU/ml. Applying the culture filtrate on rice seedlings in the greenhouse at 2 h post inoculation (HPI) with M. oryzae showed 88.3% disease reduction of rice blast, while culture filtrate application before pathogen inoculation showed even higher rates of disease reduction. Suppression of the infection process of M. oryzae on detached rice leaves was observed by light and scanning electron microscopy, showing inhibited conidial germination and reduced appressorial formation on rice leaves sprayed with culture filtrate before 3 HPI. Application of JK-1 as cells or culture filtrates to plant tissues did not cause any noticeable negative effects. These results indicate that the antifungal substance(s) in the culture filtrate of S. globisporus JK-1 can exhibit an inhibitory effect on M. oryzae and a suppressive effect on rice blast disease. Crown Copyright (C) 2011 Published by Elsevier Inc. All rights reserved.