Switchgrass root exudates have allelopathic potential on lettuce germination and seedling growth

Non-native plant species may inhibit the growth of native vegetation either by competing for resources or by secreting allelochemicals. Switchgrass (Panicum virgatum L.), a perennial grass that is adaptable to a wide range of environments, has recently been introduced to China's Loess Plateau as a forage and as a biofuel source. In this study, we assayed the allelopathic potential of root exudates from 11 switchgrass cultivars (Alamo, Blackwell, Cave-in-Rock, Dakota, Forestberg, Illinois USA, Kanlow, Nebraska 28, Pathfinder, Sunburst, and Unnamed) on lettuce (Lactuca sativa L.) germination and seedling growth. The root exudates were applied to lettuce seeds at three concentrations (1, 10, or 100 mg L-1). Germination percentage (Gp), germination speed (Gs), and allelopathic response index (RI) were calculated to compare the effects of the switchgrass cultivars. The results indicated that lettuce germination and seedling growth generally decreased as the concentration of root exudates increased. Root exudates of Forestberg generally reduced lettuce seedling growth, regardless of the concentration at which the exudates were applied. In contrast, depending on their concentration, root exudates of Nebraska 28 either had no significant effect or increased germination speed and lettuce seedling growth. Cluster analysis showed that Nebraska 28 and Forestberg had the highest allelopathic potential among the switchgrass cultivars. The allelopathic potential of Alamo and Kanlow were similar, suggesting that allelopathic potential is related to ecotype. These results provide important information for additional studies about allelopathic potential of switchgrass and about interactions between switchgrass and neighboring plants.