Potential of Trichoderma harzianum and T. atroviride to Control Botryosphaeria berengeriana f. sp. piricola, the Cause of Apple Ring Rot

Abstract Trichoderma harzianum T88 and T. atroviride T95 were tested for their efficacy in controlling apple ring rot (caused by Botryosphaeria berengeriana f. sp. piricola) in vitro and in the field. Isolates of T88 and T95 produced both volatile and non‐volatile antibiotics that suppressed mycelial growth of the pathogen. Light and scanning electron microscopy showed that mycoparasitism by Trichoderma spp. of B. berengeriana f. sp. piricola resulted in penetration and disruption of hyphal cells, and thinning of cytoplasm of the pathogen. The culture filtrates of T88 and T95 in Czapek's liquid medium suppressed conidial germination of the pathogen, and the germination level was negatively correlated with the duration of culture of Trichoderma. In inoculation tests, 32 days after simultaneous inoculation or preinoculation with B. berengeriana f. sp. piricola and Trichoderma spp., the incidence of infected apple shoots was reduced, respectively, by 65.3–76.4% and 62.5–76.4%, and the index of infection reduced by 36.9–38.9 and 40.7–44.4, The effect of inoculating B. berengeriana f. sp. piricola 3 days after the antagonists were inoculated was greater (81.4–88.8%) than simultaneous inoculation (72.2–77.8%). Re‐isolation from inoculated apple shoots demonstrated that the pathogen had been suppressed by Trichoderma. The ability to re‐isolate the pathogen from apple after co‐inoculation and pre‐inoculation with Trichoderma spp. was reduced by 27.0–42.3% and 22.2–47.1%, respectively. The biocontrol field trial suggested that the B. berengeriana f. sp. piricola canker on apple shoots and stems and rotting fruit had been efficiently controlled by the application of spore suspensions of T. harzianum T88 and T. atroviride T95. The efficacy of control by Trichoderma is thus similar to that of routine chemical control.