Evaluations of allelopathic effect of Echinochloa colona weed on rice (Oryza sativa L. 'Vandana').

Echinochloa colona (L.) Link is a very problematic weed in up land and medium land rice causing significant reduction in yield. In the present investigation, laboratory and field experiments were conducted to evaluate the nature of interaction E. colona on germination and growth of the up land rice cultivar 'Vandana'. The effects of decomposing and decomposed aqueous leachates (1-10% w/v) obtained from the dried biomass of 20, 30, 40 and 60 days old Ecolona plants were studied on rice using petridish bioassay technique with three different types of culture media like filter paper, soil, and soil + activated charcoal. The decomposing leachates of E. colona showed strong toxic effect on root and shoot growth of rice, the highest being noted with 10% leachates of 60 days old plant residue. It inhibited root and shoot growth by 100% and 43.9% respectively as compared to control. The corresponding decomposed leachates inhibited rice germination by 90% and root and shoot growth by 70 and 25% respectively. These toxic effects of leachates showed in filter paper medium were significantly reduced in soil and soil plus activated charcoal media proving their allelopathic nature. In a field experiment, E. colona and rice were grown in proportions of 1:1, 1: 2 and 1:4, the total plant density being maintained at 100 pants m(-2). The height and dry matter of rice were adversely affected with increasing in E. colona population. From another similar field trial, data on dry matter of 20, 30, 40, and 60 days old plants were taken and their plant relative yield (PRY) and relative yield total (RYT) values were calculated. The PRY and RYT values were found to be less than unit (< 1) throughout the growth period studied which suggested the presence of severe antagonistic interspecific interaction between rice and E. colona due to allelopathy.