Allelopathy Journal

Parthenium (Parthenium hysterophorus L.), an annual invasive weed native to tropical America, is rapidly spreading in many parts of the world. We studied the allelopathic potential of rice (Oryza sativa L.) to manage this weed. In laboratory bioassay, effects of aqueous, methanol and n-hexane shoot extracts (0,2,4,6,8,10% concentrations) of 3 rice varieties (Basmati-385, Basmati-386 and Basmati Super) were determined on the germination and seedling growth of parthenium. Aqueous and methanol extracts proved toxic against this weed. Generally, extracts of higher concentrations (6–10%) significantly decreased the germination, shoot length and total plant biomass. All concentrations of aqueous and methanol extracts significantly decreased the root length. Methanol extracts (10%) of Basmati 386 was most toxic to germination, shoot length, root length and plant biomass and caused 85, 87, 95 and 98% reduction, respectively.

In foliar spray bioassay, aqueous extracts (5 and 10% concentrations) of 3 rice varieties were sprayed on 7 days old pot grown parthenium seedlings and 2 subsequent sprays were done at 5 days intervals each. All extracts reduced the root and shoot biomass, however, 5% extracts were more inhibitory than 10% extract.

In residue incorporation bioassay, crushed shoot materials of 3 rice varieties were incorporated in the soil at 0.5, 1.0 and 1.5% (w/w) concentrations. Parthenium seeds were sown one week after residue incorporation and plants were harvested 4 weeks after sowing. All residue incorporation treatments (except 0.5% Basmati Super) significantly declined the shoot biomass of target weed. Highest concentration (1.5% residue incorporation) of the 3 rice varieties caused 61–81% and 38–62% reduction in shoot and root biomass of parthenium weed, respectively.