Significant in vitro antagonism of the laurel wilt pathogen by endophytic fungi from the xylem of avocado does not predict their ability to control the disease

Abstract

The ascomycete Raffaelea lauricola causes laurel wilt, a lethal vascular disease of avocado, Persea americana, and other members of the Lauraceae plant family. Few effective control measures for laurel wilt exist and new measures are needed. In this study, biological control of the disease with endophytic fungi from avocado was examined. Thirty‐two endophytes (24 operational taxonomic units or OTUs) isolated from the xylem of healthy trees (the infection court of R. lauricola) were evaluated against R. lauricola with in vitro dual‐culture assays. Nine OTUs that showed strong in vitro antagonism of the pathogen were tested in planta against laurel wilt. In three greenhouse experiments, grafted avocado plants of Simmonds or Russell cultivars, which are both susceptible to laurel wilt, were inoculated with endophytes and, after 10–16 days, inoculated with the same isolate of R. lauricola that was used in the in vitro assays. Within 14 days of inoculation with R. lauricola, laurel wilt developed in plants that were not treated with endophytes (positive controls) but also developed in endophyte‐treated plants to the extent observed in the positive controls (P = 0.05). The pathogen colonized plants rapidly and systemically, but endophytes generally did not colonize xylem more than 2 cm above the point at which plants were inoculated. Although the tested endophytes strongly antagonized the pathogen in vitro, this did not translate to an ability to reduce development of laurel wilt. The management of laurel wilt and other plant diseases with fungal endophytes is discussed.