Evaluation of the Allelopathic Activity of Aqueous and Methanol Extracts of <i>Heliotropium indicum</i> Leaves and Roots on Eight Cucurbit Crops

Allelopathy, a biological phenomenon where plants release chemicals that influence the growth and development of neighboring flora, offers potential natural alternatives for weed management in agriculture. This study investigated the allelopathic effects of <i>Heliotropium indicum</i> leaf and root extracts on the germination, growth, and biochemical parameters of eight cucurbit crops. Results demonstrated that <i>H</i>. <i>indicum</i> extracts generally inhibited seed germination across all cucurbit species, with aqueous extracts showing a stronger effect than methanol extracts in <i>Lagenaria siceraria</i> at 10.66 ± 0.46% (<i>p</i> < 0.001). The treatment also variably affected shoot and root growth, indicating both inhibitory and stimulatory actions, depending on the crop species and extract type. For instance, in methanol extract treatments, <i>Benincasa hispida’s</i> shoot length was significantly reduced, compared to the control, at 2.1 ± 0.14 cm (<i>p</i> < 0.001). Notably, aqueous leaf extracts enhanced chlorophyll content more effectively than root extracts, suggesting a potential application as a biostimulant, to improve photosynthetic efficiency in certain species, for example, <i>Momordica charantia</i> (<i>p</i> < 0.05). The study further explored the antioxidative potential of the extracts by measuring MDA levels, a biomarker for oxidative stress. MDA levels increased significantly across all species in response to both types of extracts, indicating oxidative stress (<i>L. siceraria p</i> < 0.05). These findings suggest the potential of <i>H. indicum</i> extracts as natural herbicides and biostimulants, though their effects are species-specific and dependent on concentration. This research contributes to understanding the complex interactions in plant allelopathy, and highlights the potential of plant-derived extracts in sustainable agriculture.