Abstract
Root disease suppression by ectomycorrhizal(ECM) fungi, Pisolithus tinctorius, Rhizopogon rubescens, Hebeloma cylindrosporum, and Suillus bovinus, was investigated by in vitro examination and in vivo co-inoculation of both ECM fungi and root pathogenic fungus, Fusarium oxysporum, to the ectomycorrhizal-free Pinus densiflora seedlings. Mycelial growth and sporulation of F. oxysporum were inhibited on PDA containing culture filtrates of ECM fungi from 9.3 to 18.6% and from 20.1 to 58.9%, respectively, as compared with mycelial growth and sporulation on the control medium. Spore germination was also strongly inhibited by the culture filtrates of R. rubescens for 90 days upto 81.8%. Pre- or simultaneous inoculation of P. densiflora seedlings with ECM fungi resulted in resistance of seedling roots to the infection by root pathogenic fungus, F. oxysporum, as compared with the control seedlings. The survival rate of the seedlings inoculated with F. oxysporum, and subsequently with ECM fungi was averaged by 52%, but pre- or simultaneous inoculation of ECM fungi completely protected P. densiflora seedlings against root infection by F. oxysporum. Disease suppression by ECM fungi in P. densiflora is, therefore, associated with the increase of fungitoxic or fungistatic metabolites excreted by symbiotic ECM fungi to the rhizosphere of seedlings as well as mechanical barriers, i.e., fungal mantle and Hartig net.
