First report of inhibitory abilities of dark septate endophytic fungi against white root rot disease on Hevea brasiliensis seedlings in nursery conditions

Background
The dark septate endophytes (DSE) are endophytic and non-mycorrhizal fungi with the ability to impact and control some plant pathogens and promote plant growth. The aim of this study was to investigate the effectiveness of five different DSE fungal isolates in controlling white root rot disease (WRRD) caused by the plant pathogen, Rigidoporus microporus in Hevea brasiliensis in a nursery system. There are no previous reports on the role of DSE in controlling WRRD. In this study, the efficacy of five DSE isolates, including Acrocalymma vagum SBTBMDS 1, Clonostachys chloroleuca TMDS 2.1, Lasiodiplodia theobromae APDS 3.2, Penicillium oxalicum TMDS 3.2, and Fusarium falciforme TBMDS 2.4b, was tested for their ability to reduce the severity of WRRD in vivo.
Results
The results showed that all the DSE isolates were able to inhibit R. microporus, leading to a decrease in the disease severity of WRRD, with percentages ranging from 7.50 to 17.5% and percentage of disease inhibition from 57.67 to 83.33% than the controls, which had a severity percentage of 45%. The TMDS3.2 isolate showed high efficacy in increasing the girth (137%) and height (63.3%) of H. brasiliensis seedlings, while the isolates of P. oxalicum TMDS 3.2 and F. falciforme TMDS 2.4b enhanced the dry weight (123 and 122%, respectively) than the control. Two isolates of P. oxacilum TMDS 3.2 and C. chloroleuca TMDS 2.1 increased the root volume (120 and 107%, respectively) than the control. Gas chromatography–mass spectrometry (GC–MS) analysis showed the ability of three selected DSE isolates, L. theobromae APDS 3.2, F. falciforme TBMDS 2.4b, and P. oxacilum TMDS 3.2, to produce acetic acid butyl methyl-phosphinoylmethyl ester and ethanone, 1-(4-methyl-1H(imidazol-2-yl)—that previously reported as antimicrobials.
Conclusion
This study demonstrated that DSE fungal isolates had the potential to act as a biocontrol agent against R. microporus in H. Brasiliensis seedlings. In the future, the findings of this study could be utilized to prevent WRRD, one of the most serious problems in rubber plantations, in an environmentally friendly way by reducing the usage of fungicides.