Lily (Lilium spp.) root exudates exhibit different allelopathies on four vegetable crops

Lilies are a popular ornamental and vegetable crop that has medical use. Lily cultivation has developed quickly in China but faces continuous cropping obstacles. Allelopathy is one of the main continuous cropping obstacles and is the foundation for after-crop selection in crop rotation. In this study, lily root exudates were acquired at three stages (10, 20, and 30 days) after hydroponic culture of lily bulbs, and the allelopathy of four vegetable crops was tested by bioassay. The results indicated that the allelopathy intensity of lily root exudates on radish increased with increasing duration of hydroponic culture, and the lily root exudates that were collected after 30 days of hydroponic culture exhibited the strongest allelopathic effects. The allelopathy on tomato, cucumber, and lettuce was complex. The weakest allelopathy on tomato and cucumber, but the strongest allelopathy on lettuce, was exhibited by lily root exudates that were collected after 20 days of hydroponic culture. Furthermore, differences in seed germination response and shoot and root growth patterns of the same root exudates were observed. Comparably, radish was the most sensitive receptor to the allelopathy of lily root exudates that were collected at different stages, and lettuce appeared to be the least sensitive of the tested receptors based upon the studied indices. It is inferred that lettuce and cucumber are suitable after-crops for lily, while radish is the most rational receptor for further bioassay tests on the allelopathy of lily root exudates.