Piriformospora indica promotes the growth and enhances the root rot disease resistance of gerbera

Piriformospora indica, a root endophytic fungus with growth-promoting and resistance-enhancing effects on host plants, has been successfully applied as natural biofertilizer and biological control agent. In this study, the effects of P. indica on the growth and root rot disease resistance of gerbera plants were investigated. Results showed that P. indica significantly increased the transplanting survival rate of tissue cultured seedlings, and improved the aboveground fresh weight, underground fresh weight, Fv/Fm and Y(II) values and chlorophyll content of P. indica colonized transplanted seedlings (PI). Although P. indica showed no obvious antagonistic effect on Phytophthora cryptogea, P. cryptogea inoculated PI seedlings (PP) showed much milder diseased symptoms compared with the P. cryptogea inoculated seedlings (PC). The P. indica colonization significantly increased the activities of SOD, CAT, POD and PAL, but greatly suppressed the MDA and H₂O₂ accumulations in gerbera root. The contents of some growth promoting phytohormones, such as IAA and GA, were induced by P. indica, while the ABA and JA contents was significantly inhibited. After P. cryptogea inoculation, the SOD, POD, CAT and PAL activities and IAA and GA contents decreased in PC but increased in PP. Besides, ABA and JA contents in PP were significantly lower than in PC. Our results indicated that P. indica improved the gerbera growth by increasing chlorophyll content, photosynthetic characteristics and growth-beneficial phytohormones' accumulations. Moreover, it appeared to confer gerbera with root rot resistance through increasing POD, CAT and SOD activities, stimulating IAA and GA accumulations, and suppressing ABA and JA biosynthesis.