Trichoderma combined with palm kernel shell biochar promotes root health and rhizosphere biodiversity in young oil palm seedlings infected with Ganoderma boninense

Oil palm (<i>Elaeis guineensis</i>) contributes up to 3% of gross domestic product (GDP) in Malaysia. Long-term monoculture production reduced natural biodiversity and increased severe threat by <i>Ganoderma boninense</i>, a causal agent of basal stem rot (BSR) disease. BSR recorded projections of 860,610 hectares of plantations to be devastated by BSR by 2040. While disease management has prioritised good sanitation practices, <i>Trichoderma</i> spp. is a potential solution to combatting <i>G. boninense</i>. In this study, we determined the efficacy of <i>Trichoderma</i> spp. isolate 4A added to palm kernel shell (PKS) biochar (T-mix) to improve oil palm root health. Three-month-old seedlings were observed in control treatments, T1 to T4 and <i>Trichoderma</i> sp. treatments, T5 to 12 with Ganoderma added in T7,8, 11 and 12. Root development parameters such as root architecture, length, diameter, and surface area were observed every two months for six months. Root length of T5 (3.3 m) and T9 (4.4 m) was higher than no-treatment control, T1 (2.5 m) indicating <i>Trichoderma</i> sp. support of root health. T9 (T-mix) has significantly improved root architecture in root scan with denser and multiple root branches as while all other diseased oil palms exhibit stunted roots. The diameter of roots shows similar trend to root length of T9 roots with the highest reading at 5.4 mm. T11 showed the overall improved fungal biodiversity at 6 months post inoculation with potential disease suppressive effects against other common pathogens such as <i>Fusarium</i> sp. This study highlights a new perspective of <i>Trichoderma</i> spp. treatment with biochar to provide protection to growing young oil palm root health, beyond disease control, indicating a beneficial role for early application at seedling stage. For long term application, <i>Trichoderma</i> spp. combined with biochar support healthy fungal dynamics without over-dominating indigenous fungal inhabitants. This is the first study to highlight the role of combined <i>Trichoderma</i> spp. and biochar in influencing the root architecture and rhizosphere dynamics of a perennial oil palm at the seedling stage. Overall, this study presents an exciting opportunity to use a new <i>Trichoderma</i> sp.-biochar solution in the battle against <i>G. boninense</i>.