Identification of allelochemicals in rice root exudates at various phenological phases and their influence on barnyardgrass

This study was conducted to identify the allelochemicals from rice (Oryza saliva L.) root exudates at various phenological phases and to evaluate their allelopathic effects on growth of barnyardgrass (Echinochloa crus-galli P. Beauv. var. oryz-cola Ohwi). The root exudates of allelopathic varieties (Sathi, Jinmi and Nongan) contained more allelopathic substances than non-allelopathic variety Ilpum (control). The root exudates of rice varieties at different phenological phases contained compounds such as benzene and phenol derivatives, several long-chain fatty acids, benzoic acid and sterols in GC-MS analysis. The phthalic acid (1,3-benzenedicarboxylic acid), an environmental hormone was also identified and its allelopathic potential needs to be further examined on paddy weeds. Many allelochemicals, such as long-chain fatty acids, phenols and benzene derivatives were found only at the yellowing stage. The allelopathic effects of root exudates significantly inhibited the height, number of tillers and total dry weight of barnyardgrass plants, when compared with non-allelopathic varieties. This study identified allelochemicals in rice root exudates at several phenological phases and showed a relationship between root exudates and the inhibition of barnyardgrass growth.