allelopathic effects of shoot and root water extracts of hoary cress (cardaria draba) on germination characteristic and seedling growth of sorghum (sorghum bicolor l.)

a growth chamber study was carried out to evaluate the allelopahtic effects of shoot and root water extract of hoary cress (cardaria draba) on seed germination and seedling characteristic of sorghum (sorghum bicolor). the study was conducted based on completely randomized design with four replications in research laboratory of faculty of agriculture, university of birjand in 2008. treatments were four levels (25, 50, 75 and 100%) of shoot, root and their mixed water extracts of cardaria draba with distilled water as control. results showed when concentration of shoot and root extracts increased, germination percentage, germination rate, root length, stem length, root fresh weight, stem fresh weight, seedling fresh weight, root/stem fresh weight ratio and root/stem length ratio decreased significantly. in the concentrations of 75 and 100 percent of allelopahtic extract no germination was recorded. the functional three-parameter logistic model provided a successful estimation of the relationship between water extract levels and germination response of sorghum. the fitted model showed that the 50% concentrations of all organs extract caused 50% reduction in maximum germination percentage of sorghum. the highest and lowest slope of the model was observed in shoot and root tissues water extract, respectively. there was not significant difference between the 25% concentration of all organs extract, the 50% concentration of root extract and control when studied the time to 50% of maximum germination percentage. based on orthogonal comparisons, shoot, mixture and root water extract had the most inhibition on germination percentage, root and stem length, respectively.