Allelopathic potential of invasive Acacia holosericea on germination and growth of selected paddy varieties

Several Acacia species have been shown to have allelopathic effects which could potentially affect crop production such as rice. This study aimed at evaluating the allelopathic potential of invasive A. holosericea on germination and growth of two Oryza sativa varieties in Brunei Darussalam i. e. Bario and Laila. The paddy seeds were treated for 12 days with the aqueous crude extract, obtained from either the brown leaf litter or fresh green leaves (phyllodes). Germination was not significantly affected except when 10 mg/ml of the green phyllode extract was used, which reduced the number of germinated Laila seeds by ∼10%. The radicle length of germinated Bario seeds was significantly reduced when ≥5 mg/ml of either the brown or green phyllode extract was used. Interestingly, for Laila, a significant reduction in the radicle length was observed at ≥1 mg/ml of either extract, indicating Laila was potentially more sensitive than Bario. At 10 mg/ml, a ∼80–90% reduction in the radicle length was observed for both the paddy varieties. The shoot of germinated seeds, which was significantly reduced only at higher extract concentrations, was less affected compared to the radicle. Similarly, Laila was potentially more sensitive than Bario, with up to ∼40–50% shoot reduction but only ∼30% reduction was observed in Bario. Consequently, this study showed that A. holosericea had allelopathic potential, which could have implications on agricultural and ecological management.