Although a wide variation in traits was observed among cultivars, none of them gave satisfactory yield under aerobic conditions. Binadhan-5 emerged as the most productive, whereas BRRI dhan59 appeared as the most weed suppressive rice variety. The least productive cultivar was BRRI dhan55, which was closely followed by Binadhan-8and BRRI dhan58. Based on reports in earlier studies , the present study included a variety of commonly cited traits including plant height, tillering ability,early visual vigor, duration, and SPAD values. Significant variations among the varieties were recorded suggesting that selection based on those traits was practical.Plant height is considered as desirable characters for weed suppressive cultivars.Although plant height varied widely among the cultivars, early plant height i.e. height at 30DAS was strongly and negatively correlated with weed dry weight. Earlier and faster growth allowed the rice crop to compete with weeds for plant resources, and this was reflected in the crop yield.Early visual vigor or vigor index, a reliable predictor of crop biomass integrating both height and tiller number, is an important selection criterion for weed competitiveness. Vigor rating is rapid, non-destructive, less labor-intensive and reliable, and therefore a promising and feasible tool for making decisions on weed competitiveness.In this study, early visual vigor varied widely among varieties, and its strong correlation with other parameters confirms its acceptability.It has been reported previously that early season vigor is directly linked with the competitive ability of the crop and later in the crop growing season, it confers competition against weeds .
The SPAD meter provides a very easy, swift and non-destructive method for estimating relative leaf chlorophyll content.Higher SPAD values indicate greener healthier plants. The results showed SPAD values varied among the varieties. SPAD values were greatly reduced by weed interference and this was reflected in yield performance. Weed interference negatively and markedly affected all yield components which cumulatively impaired grain yield. The rice varieties used in the current research showed wide diversity in relative yield loss, which ranged from 43% to 82%. Weed biomass was strongly and negatively correlated with grain yield, indicating that weed suppressive ability can be combined with yield potential. Anwar et al.and McGregor et al.also observed a similar relationship. Weed interference negatively and markedly affected all yield components which cumulatively impaired grain yield. Weed biomass was strongly and negatively correlated with grain yield,cannabis grow tray and positively correlated with relative yield loss indicating that weed suppressive ability can be combined with yield potential. Medicinal plants are considered as an important source of secondary metabolites that usually have a number of biological functions. It has been reported that medicinal plants species possess strong allelopathic potential. Many researchers around the world are now showing their keen interest on medicinal plants for searching new natural plant products,. Islam and Kato-Noguchistated two reasons for this increasing interest: 1) the easier screening process of phytotoxic plants from medicinal plants and 2) the possibility to have more bioactive compounds in medicinal plants than other plants. Fu-jii et al.carried out the first comprehensive studies of allelopathic medicinal plants.
They evaluated 387 Japanese medicinal plants and observed that a considerable number of those have growth inhibitory potential . Azizi et al. examined 56 aromatic medicinal plants of 22 families from Iran for their allelopathic potential and found 51 species inhibited the seedling growth of lettuce. Gilani et al. also evaluated 81 medicinal plant species of Pakistan and reported 78 as allelopathic potential inhibiting the root growth of lettuce. Mardani et al.recently evaluated the allelopathic potential of 83 Iranian medicinal plants and observed more than 80% root growth suppression of lettuce by Peganum harmala, Berberis vulgaris, Artemisia aucheri and Ferulago angulata. Amini et al.investigated the allelopathic potential of 68 medicinal and wild plant species belong to 19 plant families grown in Iran. Since the inception of agriculture, different types of natural plant products have been used to control pests mainly insect and disease organisms. More evidences have been found in the world literature about the use of natural product as fungicides, insecticides, and other pesticides than as herbicides . Although natural product based herbicides for weed control strategies have not yet been as successful as like other pesticides, however, there have some notable success stories . Nowadays, the use of allelopathic medicinal plants has been suggested as a viable option for alternative weed management in sustainable agriculture . Yang and Tang , described two ways of plant utilization for weed management: 1) the active compounds are isolated, identified and chemically synthesized; if possible, these compounds or their active analogs are produced by the chemical industry, 2) plant tissue or a crude product of the plant, such as aqueous or organic extract is used directly.