A. K. M. Mominul Islam

Phytotoxic Activity of Ocimum tenuiflorum Extracts on Germination and Seedling Growth of Different Plant Species

Phytotoxic activity of Ocimum tenuiflorum (Lamiaceae) plant extracts was investigated against the germination and seedling growth of cress (Lepidium sativum), lettuce (Lactuca sativa), alfalfa (Medicago sativa), Italian ryegrass (Lolium multiflorum), barnyard grass (Echinochloa crus-galli), and timothy (Phleum pratense) at four different concentrations. The plant extracts at concentrations greater than 30 mg dry weight equivalent extract mL−1 reduced significantly the total germination percent (GP), germination index (GI), germination energy (GE), speed of emergence (SE), seedling vigour index (SVI), and coefficient of the rate of germination (CRG) of all test species except barnyard grass and GP of lettuce. In contrast, time required for 50% germination (T 50) and mean germination time (MGT) were increased at the same or higher than this concentration. The increasing trend of T 50 and MGT and the decreasing trend of other indices indicated a significant inhibition or delay of germination of the test species by O. tenuiflorum plant extracts and vice versa. In addition, the shoot and root growth of all test species were significantly inhibited by the extracts at concentrations greater than 10 mg dry weight equivalent extract mL−1. The I 50 values for shoot and root growth were ranged from 26 to 104 mg dry weight equivalent extract mL−1. Seedling growth was more sensitive to the extracts compared to seed germination. Results of this study suggest that O. tenuiflorum plant extracts have phytotoxic properties and thus contain phytotoxic substances. Isolation and characterization of those substances from this plant may act as a tool for new natural, biodegradable herbicide development to control weeds.

Effectiveness of Integrated Weed Management in Five Varieties of Aromatic Rice in Bangladesh

Thousands of rice land races are considered to exist in Bangladesh (Haque and Miah, 1990). Each of them possesses some special characteristics. Only some of these are unique for quality traits including fineness, aroma, taste and protein contents. Bangladesh has a stock of above 8,000 rice germplasms of which nearly 100 are aromatic (Islam et al., 2016). Cultivation of this rice has been gaining popularity in the country over the recent years, because of its huge demand both for internal consumption and export (Das and Baqui, 2000). About 27% of the total rice cropped area (BBS, 2003), and 12.5% of the total monsoon rice (BBS, 2005) are occupied by aromatic fine rice varieties of Bangladesh. Moreover, the production of aromatic fine rice is profitable due to its high price over low price coarse milled rice (Raju and Reddy, 2000; Sikdar et al., 2008). Recently, some aromatic fine rice varieties being cultivated in Bangladesh are of international standard and attracting the buyers in the global markets. However, the yield of aromatic rice was lower (1.5–2.0 t ha) than the coarse rice (Islam et al., 2010). Weeding has a great influence on the performance of the associated crop (Kumar and Chopra, 2013, 2016). Thus the best weeding practice needs to be adopted by the farmers with a view to reducing weed infestation and maximizing rice yield. Mechanical and manual methods of weed controls are mainly practiced by the farmers that are very much laborious and time consuming (Kumar and Chopra, 2013, 2016). Moreover, the availability of labor is decreasing due to the out migration of agricultural labors to industries with higher wages than agriculture, increases the need of using herbicides. Use of herbicides may be an alternative method in controlling weeds more easily and effectively at low cost (Rashid et al., 2007). But no single herbicide can control all weeds effectively in all environments. To date very few studies have been conducted to find out the best weed management practices for aromatic rice. On the other hand, a suitable combination of variety and weed management practices might be helpful to increase the yield of aromatic rice. Information on the varietal performance of aromatic rice and its management practices ORIGINAL RESEARCH ARTICLE