Allelopathic potential of rice halls on germination and seedling growth of barnyardgrass

Hull extracts from 91 cultivated rice cultivars (Oryza sativa L.) were used to determine their allelopathic potential on seed germination and seedling growth of barnyardgrass (Echinochloa crusgalli P. Beauv. var. oryzicola Ohwi). The allelopathic effects of various concentrations of hot and warm water hull extracts from selected cultivars were also investigated. In the initial screening the 'SR31' extract inhibited germination 59%. The length and dry weight of roots were more affected by hull extract than the shoots. The greatest fetal seedling length and dry weight inhibition was from the 'Janganbyeo' warm extracts and was 75 and 96%, respectively. Rice cultivars demonstrating significant allelopathic potential were compared using varying concentrations with a hot or warm extraction procedure. The two extraction procedures displayed different ultra violet (UV) absorption, pH, electrical conductivity (EC), and osmotic potential. Warm extracts exhibited a lon-er percentage absorbance in the UV range, higher percentage absorbance in the visible range, higher EC (S m(-1)) and osmotic potential (kPa), and showed lower pH than those of hut extracts. As concentration increased, the warm extracts had a greater inhibitory effect on barnyardgrass germination, seedling growth, weight, and caloric content than the hot extracts. The greatest inhibi tion occurred when the highest concentration (8 g L-1) warm water extract was applied. These results suggest that rice hull extracts may be a source of natural herbicide, and warm water may extract more allelochemicals than hot water, There may he genetic differences among rice cultivars for allelopathic potential on barnyardgrass. The breeding of rice cultivars with greater allelopathic potential may be possible.