Effectiveness of Trichoderma as a biological agent to control Cylindrocladium causing black root rot in avocado seedlings

Black root rot caused by Cylindrocladium sp. has recently emerged as a serious threat to avocado (Persea americana Mill.) production, leading to severe root decay, stunted growth, and seedling mortality. This study evaluated the antagonistic poten­tial of Trichoderma sp. as a biological control agent against Cylin­drocladium through both in vitro and in vivo experiments. Dual culture assays on potato dextrose agar (PDA) demonstrated that Trichoderma sp. significantly inhibited mycelial growth of Cylindrocladium, with inhibitory power progressively increasing from 21.16 ± 5.0% at day 3 to 59.17 ± 7.3% at day 7. Greenhouse trials were then conducted using avocado seedlings under six treatments: control, only Trichoderma, only Cylindrocla­dium, Trichoderma applied seven days before Cylindrocladium, Cylindrocladium applied seven days before Trichoderma, and simultaneous inoculation. Results revealed that Trichoderma application prior to pathogen inoculation markedly reduced disease occurrence (37.50%) and disease severity (27.50%). Although growth responses were not consistently significant, this treatment showed numerically higher plant height and root dry weight than the pathogen-only treatment. Conversely, treatments where Trichoderma was applied after or simultane­ously with Cylindrocladium were less effective, highlighting the importance of timing in successful biocontrol. Although minor contamination was observed in the control treatment, the over­all findings consistently demonstrated the suppressive effect of Trichoderma against black root rot. This study confirms that pre-application of Trichoderma enhances seedling resistance by colonizing the rhizosphere and reducing pathogen establish­ment, thereby promoting healthier growth. These results pro­vide strong evidence that Trichoderma sp. can be integrated into nursery management practices as an eco-friendly and sustainable strategy for controlling black root rot in avocado seedlings.