Allelopathy of invasive Tithonia diversifolia (Hemsl) A. Gray on Pisum sativum L. and its linkage with canopy openness in a global biodiversity hotspot

Allelochemicals are the secondary metabolites present in the leaves or other parts of the invasive alien plants that can either stimulate or inhibit the development of the native plants. To this end, an emerging invasive plant, i.e., Tithonia diversifolia from Asteraceae is inadequately explored in terms of allelopathy, especially in relation to its influence on the germination and growth of edible crops. Thus, the present study aims to study its allelopathic effect on common bioassay crop i.e., Pisum sativum, grown in Mizoram to help validate the ‘novel weapon hypothesis (NWH). In addition, the ecological investigation was performed with respect to the canopy openness, leaf area index (LAI) and photosynthetically active radiation (PAR) as they can be inextricably linked with invasive spread and modulation of allelopathy. Results showed that with increase in the concentration of T. diversifolia derived fresh leaves aqueous extracts (FLE), the growth parameters (rate of seed germination, seed radicle, seed plumule and biomass) of P. sativum decreases, which may be ascribed to the inhibitory effect of allelochemicals. Last, the study also observed that the higher canopy openness facilitates the spread of T. diversifolia due to high light availability, while the lower canopy gaps restrict the growth of T. diversifolia. Henceforth, in control/containment perspective, the sustenance of intact canopy can sustainably manage and reduce the T. diversifolia infestation in agriculture systems by alleviating its field allelopathic effects on edible crops, thereby help maintain crop yield and food security.