Effects of Autotoxicity and Allelopathy on Seedling Growth in Cashew (Anacardium occidentale L.)

Cashew (Anacardium occidentale L.), a vital tropical cash crop, may face yield declines in old plantations due to unexplored risks of autotoxicity. This study investigated the allelopathic and autotoxic potential of cashew plant under laboratory and greenhouse conditions. The laboratory bioassays with leaf and stem bark (10–200 mg) demonstrated a strong allelopathic effect, reducing lettuce radicle elongation to 7–46.0% and 9–79% of the control, respectively. Aqueous leaf extract (50 mg/mL) completely inhibited (0%) lettuce seed germination and reduced pepper germination to 42%. However, the root exudate of cashew seedlings did not have any inhibitory effect on the test plants. Greenhouse experiments simulating field litter fall revealed significant autotoxicity in cashew. Cashew seedlings grown in growth media amended with 10% cashew leaf powder exhibited severe growth suppression after 13 weeks, including a reduction in plant height by 58.2% compared to controls. Chlorophyll content, stem girth, and leaf number were also significantly reduced. This study concludes that cashew possesses significant allelopathic properties and a clear potential for autotoxicity, as directly evidenced by the suppressed growth of its own seedlings following the incorporation of leaf powder. These findings identify autotoxicity, mediated through leaf litter decomposition, as a critical risk factor for the replanting success and long-term sustainability of cashew orchards, necessitating further investigation into management strategies.