International Journal of Scientific and Research Publications, Volume 4, Issue 7, July 2014 1 ISSN 2250-3153 www.ijsrp.org Assessment of allellopathic potential of some traditional rice cultivars in Sri Lanka Ranawake AL*, Amarasinghe UGS, Dahanayake N * Department of Agricultural Biology, Faculty of Agriculture, University of Ruhuna, Sri Lanka Abstract- Allelopathy refers to the chemical inhibition of growth of one species by another. With the objectives of understanding allelopathic effects of sixty seven traditional rice cultivars, a field experiment and laboratory experiments were carried out in 2011 Yala season at Faculty of Agriculture, University of Ruhuna, Mapalana, Sri Lanka. Rice cultivars were transplanted according to the completely randomized block design with four replicates. Each replicate consisted of three rows of rice plants and data were collected from the middle row. After three months of transplanting, plant height (cm) and number of tillers/plant, were evaluated in traditional rice cultivars and total dry matter weight of weeds in 0.093 m 2 (1ft2) area encircled by the rice plant were evaluated in three replicates. According to the statistical analysis there were significant differences in plant height and tiller number/plant in traditional rice cultivars. Further there was a significant difference in average dry matter weight of weeds in 0.093 m 2 area encircled by the plant of rice cultivar but there were no correlations in between plant height of traditional rice cultivar or tiller number/plant of them with average dry matter weight of weeds in 0.093 m2 area encircling rice plant emphasizing the non- significant effect of rice plant morphology in weed density. Separate experiments were carried out to see the allelopathic effects of these rice cultivars on germination of Barnyard grass (Echinochloa crusgalli L.) seeds. In one set of experiment three soil samples were collected from the soil area contacted with root system of the middle row rice plants in three row design. Twenty Echinochloa crusgalli L. seeds were sawn in soil samples and watered according to the necessity. After one month, germination percentage of Echinochloa crusgalli (L.) was evaluated. In the other set of experiment, each 5 g of leaf sample from individual traditional rice cultivar were crushed and mixed with non-rice grown soil samples in three replicates. Twenty seeds of Echinochloa crusgalli (L.) were sawn in each soil sample and germination percentage was counted one month after the seeding. According to the statistical analysis, there were significant differences in germination percentage of Echinochloa crusgalli L. in both soil types while germination percentage was significantly lower in soil samples collected from rice root zone. Furthermore, there was a strong correlation in between germination percentage of Echinochloa crusgalli (L.) in two types of soil samples. This study reveals the allelopathic effect of individual traditional rice cultivar on weeds in field condition and allelopathic effect of them on seed germination of Echinochloa crusgalli (L.) in root exudates and in leaf extracts as well. Root exudates of traditional rice cultivars Murunga, Ran ruwan, Mudaliwi, Kirikara, Kahata Samba Molligoda Kalukanda and Sivuru wee significantly suppressed the seed germination of Echinochloa crusgalli while leaf extracts of rice cultivars Rathel, Sudu samba, Kalu heenati, Mahakuru wee, Kotanavalu, Galpa wee, Yakada wee, Gonabaru, Muthumala and Seedevi significantly reduced the seed germination of Echinochloa crusgalli L. which emphasizes the potential usage of these rice cultivars for weed management after reconfirmation of the allelopathic effect. Index Terms- Allelopathy, germination percentage, leaf extract, root exudates, traditional rice, weed density I. INTRODUCTION llelopathy is the effect of one plant or microorganisms on growth of another plant or micro organism by releasing some chemical compounds into the environment (Rice et al. 1984) and it is a component of integrated weed management technology to reduce the herbicide use for sustainable agricultural development. This is an eco-friendly alternative approach to conventional weed control method, hence, exploitation of local resources to dissect the allelopathetic effect of known plants are timely needed. The rice allelopathy may be one of the potent methods for sustainable agricultural system. Rice has been studied for allelopathic effects in different bio assays (Chou et al. 1991; Hassan et al.1996; Maneechote et al. 1996; Ebana et al. 2001 and Kong et al. 2002). Results of Olofsdotter et al. (1889, 1999), Kraus et al. (2002), Kitazawa et al. (2005), and Kim and Shin (2008) have convinced the potential of rice allelopathy on controlling weeds in different ways. Though there is a real need for convenient, reliable, economical, efficient and repeatable universal methodology for screening rice for allelopathy, as cultivar shows different responses depending upon the screening method used, still such method has not been recommended. Crops or weeds such as Echinochloa crusgalli L. (Maneechote et al. 1996), Nutgrass flat sedge (Hussan et al. 1996) and lettuce (Fujii et al. 1992) have been used as biological determinants in such allelopathy studies. Allelopathic effect and competitive traits of rice cause weed suppression under field conditions. The critical period for yield reduction of rice due to weeds is the first month of the crop growth and during this period expression of allelopathy in rice is prominent (Olofsdotter, 2001). Root exudation, leaching by dews and rains, and volatilization or decaying plant tissue from allelopathic plants results in release of compounds into the environment (Rice, 1984). These compounds have been identified as alkaloids, flavonoids or phenolic compounds (Chau et al., 1999). A