Application of Dose-response Models for Allelopathic Effects of Saffron (Crocus sativus) Petals on Seedling Growth of Weeds and Crops

In order to investigate the allelopathic effects of crocus petals on seedling growth of sorghum (Sorghum bicolor), wheat (Triticum aestivum), barnyard grass (Echinochloa crus-gali) and wild pigweed (Amaranthus retroflexus), five dilutions of 1% aquatic extract were prepared as 0, 10, 30, 60, and 100% of full strength. Five milliliters of each dilution was added to petri dishes containing 25 seeds laid between papers. After 10 days, plumule and radicle length was measured. Log-logistic model was fitted to radicle length response of sorghum, wheat and barnyard grass via extract concentrations but for wild pigweed the Gompertz model was better. Based on EC50 of radicle length, the sensitivity order of plants was pigweed, sorghum, barnyard grass and wheat. The five-parameter models including hormesis term were best suited for plumule length response of wheat and barnyard grass and pigweed to different concentrations. The hormesis phenomenon was observed for lower concentrations than 50% and dose giving maximum stimulation for wheat, barnyard grass and pigweed was 10.76, 12.33 and 14.02%, respectively. Germination percent was not affected by aqueous concentrates at the test plants except of pigweed that had been reduced significantly by the full strength of concentration.