Screening of Nonpathogenic Fusarium Species Suppressing Fusarium Crown and Root Rot in Asparagus Using Wheat Bran as...

Fusarium crown and root rot (FCRR), caused by the fungus Fusarium oxysporum f. sp. asparagi, is one of the most destructive diseases affecting asparagus worldwide. Despite evidence of the suppression of FCRR by several nonpathogenic F. oxysporum sensu lato strains in laboratory experiments, biological control trials in FCRR-infested fields have not consistently demonstrated the effectiveness of these strains. Therefore, we screened nonpathogenic Fusarium spp. strains for the biological control of FCRR with the modified inoculation method considering the colonization to soil of biocontrol agents (BCAs). Two strains from different lineages (SM007 and FAoc5), inoculated by irrigating a bud-cell suspension and applying cultured wheat bran medium around the root of the transplants, effectively suppressed FCRR on young asparagus seedlings. These strains also suppressed FCRR on mature second-year plants to some extent by the application of cultured wheat bran medium as an inoculation carrier. Both strains exhibited the capacity to impede chlamydospore germination of the pathogen when glucose was incorporated into soil. Although SM007 sometimes failed to show biocontrol effects, differences in efficiency appeared to be related to the fungal density colonizing wheat bran medium. These results suggest that the screened strains interact with the pathogen and also that the amount of BCAs introduced into soil is closely related to their biocontrol efficacy.