Herbicidal activity of Withania somnifera against Phalaris minor.
Herbicidal activity of Withania somnifera (L.) Dunal. was studied against Phalaris minor Retz., one of the most problematic weeds of wheat in Pakistan. In laboratory bioassays the aqueous, methanol and n-hexane extracts of 5, 10 and 15% w/v (fresh weight basis) of the roots and shoots of W. somnifera were applied. Extracts in the different solvents exhibited markedly variable herbicidal activities against germination and seedling growth of the target weed species. The methanol extracts showed the highest toxicity. Different concentrations of methanol shoot and root extracts declined the germination of P. minor by 21-71%, its shoot length by 40-72%, its root length by 50-99% and the plant biomass by 32-83%. The aqueous extracts proved to be comparatively less toxic than the methanol extracts, where generally the highest concentration of 15% exhibited pronounced toxicity against the target weed species. There was up to 48, 51, 99 and 55% suppression of the weed's germination, shoot length, root length and plant biomass, respectively, due to the 15% aqueous root and shoot extracts. Generally, the n-hexane extracts of both roots and shoots exhibited insignificant or stimulatory effects against weed shoot length and plant biomass. In a foliar spray bioassay, aqueous and methanol shoot extracts of 10% w/v (dry weight basis) concentration were sprayed on one- and two-week old pot grown P. minor seedlings. Two subsequent sprays were carried out at five day intervals each. The aqueous extract significantly reduced the shoot and root dry biomass of one-week old P. minor plants. In a residue incorporation bioassay, crushed shoots of W. somnifera were incorporated in the soil at 1, 2, ... 5% w/w. Phalaris minor seeds were sown one week after residue incorporation and plants were harvested 45 days after sowing. The lower concentrations of 2 and 3% significantly reduced, while higher concentrations of 4 and 5% of residue incorporation completely arrested, the germination of P. minor. The present study concludes that both roots and shoots of W. somnifera contain herbicidal constituents against P. minor.
Javaid
Arshad
A
Institute of Plant Pathology, University of the Punjab, Lahore, Pakistan. arshadjpk@yahoo.com
Shafique
Shazia
S
Shafique
Sobiya
S
D018525:Germination / Q000187:drug effects; D006540:Herbicides / Q000737:chemistry* / Q000494:pharmacology*; D006586:Hexanes / Q000737:chemistry; D000432:Methanol / Q000737:chemistry; D031783:Phalaris / Q000187:drug effects*; D010936:Plant Extracts / Q000737:chemistry / Q000494:pharmacology*; D018517:Plant Roots / Q000737:chemistry; D018520:Plant Shoots / Q000737:chemistry; D036226:Seedlings / Q000187:drug effects; D032341:Withania / Q000737:chemistry*
D006540:Herbicides; D006586:Hexanes; D010936:Plant Extracts; C026385:n-hexane; D000432:Methanol