The Dark Septate Endophyte, Phialocephala fortinii J2PC4, Mitigating Southern Rice Black-Streaked Dwarf Disease and Lethal to White Back Planthopper

• Southern rice black-streaked dwarf disease is a severe threat that causes huge losses. • Southern rice black-streaked dwarf virus is transmitted by the white-backed planthopper. • Dark septate endophytes have been used to combat disease as biocontrol agents. • Phialocephala fortinii J2PC4 promoted the growth and had some biocontrol effect. Southern rice black-streaked dwarf disease (SRBSDD), caused by the southern rice black-streaked dwarf virus (SRBSDV) which is transmitted by the white-backed planthopper (WBPH), is a severe disease that causes huge production losses in Southeast Asia, including China. This study aimed to explore a better control technology of the dark septate endophyte (DSE) fungi against SRBSDD and WBPH to develop an efficient approach for plant health and fitness improvement. Phialocephala fortinii J2PC4 as one promising fungal isolate was selected based on its excellent performance in symbiosis with rice. Phialocephala fortinii J2PC4 can significantly promote the growth of the rice with plant height (14.8%), fresh weight (59.5%), and dry weight (60.5%) much higher than the control. Notably, our results revealed that this isolate also possessed superior growth promotion activities as well as disease and pest suppression by significantly increase plant height（22.4%）, fresh weight (74.0%) , and dry mass (32.4%). After being infested with pests for 48 hours, the WBPH mortality rate in the P . fortinii J2PC4 treatment was greater (8.2%) than the control (1.5%). The disease incidence of SRBSDD in the Phialocephala fortinii J2PC4 treatment was significantly lower than the control, and the suppressive efficiency was 28.5%. Phialocephala fortinii J2PC4 colonization of rice seedlings decreased the malondialdehyde (MDA) content, increased the superoxide dismutase (SOD) and peroxidase (POD) activity of rice leaves; and led to resistance-related genes AOS , PR1a, and PR1b significant up-regulation expression, while POX1 and OsSAUR2 down-regulated expression. Furthermore, WBPHs spawning scale in the P . fortinii J2PC4 treatment was 24.7% lower than the control. Our results provide new insights in the application of DSE fungus P . fortinii J2PC4 as a biofertilizer and biocontrol agent can potentially be applied in the development of new, safe and effective treatments as an alternative to chemical fertilizers and fungicides for sustainable crop protection.