Effect of aqueous root and shoot extracts of weeds on germination and seedling growth of cotton

Eleven competitive weed species of cotton fields were evaluated for their allelopathic potential against cotton crop. In lab bioassays, whole plant extracts (1:10 w/v) of Trianthema portulacastrum L., Cynodon dactylon L., Cyperus rotundus L., and Boerhaavia diffusa L., significantly inhibited the germination of cotton varieties LRA 5166 and MCU 7. The roots and shoots aqueous extracts (10, 20, and 30%) of weeds inhibited germination and seedling growth of test crop. The maximum inhibition in seed germination of cotton over control was caused by root extract of C. rotundus (73.09%), followed by shoot extract of T. portulacastrum (70.24%) and root extract of C. dactylon (60.22%). The shoot extract of T. portulacastrum reduced the seedlings growth of cotton followed by the root extracts of C. dactylon, C. rotundus and shoot extract of Echinochloa colona. The root and shoot extracts of the weeds had variable allelopathic influence on cotton seed germination and growth. In pot experiments, incorporation of dry weed residues drastically reduced the germination. T. portulacastrum and C. dactylon at 5% caused 24.3 and 29.3% reduction in cotton seed germination. Radicle elongation was more sensitive than the hypocotyl growth. Reduction in mitotic division at root tip was more with 5% root extracts of C. dactylon followed by shoot extracts of T. portulacastrum and C. rotundus indicating their role in inhibiting cell division.