Biological Characteristics and Antimicrobial Activity of Endophytic sp. TQR12-4 Isolated from Elite Cultivar Ham Yen of Vietnam.

Ham Yen orange ( Lour) is the highly valuable commercial fruit of Vietnam. With the blooming of fruit production and farming area, this specialty crop is facing threats from several serious diseases; therefore the search for new effective biocontrollers is required to prevent the existing excessive use of fertilizers and plant protection chemicals. Endophytic actinomycetes are of great scientific interest due to their high potential of application in agriculture and pharmaceutical research. In this work, endophytic actinomycetes were isolated from a native orange species of Northeast mountainous province Tuyen Quang. Among 49 isolates obtained, the isolate TQR12-4 strongly inhibited test pathogens , , , and . This isolate gave comparatively high biomass yields on different substrates, for example, carboxy methyl cellulose, starch, protein, and chitin, within a wide range of temperature from 15 to 45°C and pH from 4 to 10. Sequence analysis of 16S rDNA gene showed that TQR12-4 shared 99% similarity to ; however, it slightly differed from the latter in spore morphology and hence was named as sp. TQR12-4. A thermostable antifungal substance of nonpeptide nature produced by sp. TQR12-4 had MIC against of 100 g/mL and 400 g/mL respective to extract fractions and .