ALLELOPATHIC EFFECTS OF PARTHENIUM HYSTEROPHORUS L. ON EARLY CROP ESTABLISHMENT A CONCENTRATION-RESPONSE STUDY IN RICE, GREEN GRAM, AND MAIZE

Abstract

Parthenium hysterophorus L. is an invasive weed with a chemically mediated competitive advantage that may suppress crop establishment through allelopathy. This study quantified the effects of aqueous Parthenium leaf extract on seed germination and early seedling growth of rice (Oryza sativa L.), green gram (Vigna radiata L.), and maize (Zea mays L.). Leaves collected before flowering were shade dried, extracted at 10 g 100 mL⁻¹ for 24 h, and diluted to 2, 4, 6, 8, and 10%; distilled water served as the control. Ten seeds per Petri dish were evaluated in a completely randomized design with four replicates. Germination, plumule and radicle length, dry matter, and vigour index were measured. The response was strongly concentration dependent. At the final observation, rice germination declined from 100% in the control to 46.5% at 6% extract and 0% at 8–10%; green gram declined to 47.5%, 20%, and 0% at 6, 8, and 10%, respectively; and maize declined to 60%, 35.5%, and 20% at the same concentrations. Radicles were more sensitive than plumules. At 6% extract, vigour index fell to 57.6 in rice, 213 in green gram, and 328 in maize, compared with untreated values of 1263.7, 2082, and 3160. At 10%, rice and green gram had no measurable seedling growth, while maize retained only 0.48 cm plumule and 0.03 cm radicle growth. The findings demonstrate that Parthenium leaf residues can impose severe establishment risk at concentrations likely to occur near decomposing biomass, and that germination alone underestimates injury because root elongation and vigour decline earlier. Crop-safe residue management should therefore prevent direct contact between fresh or incompletely decomposed Parthenium biomass and germinating seed.