Behavioral Responses of Tomato Plants to Cultivated Varieties of Potato‐Onion

Plants adjust growth and root allocation by recognizing neighboring plants’ genetic traits, crucial for symbiosis. However, the response of tomato ( Solanum lycopersicum L.) to various allelopathy from potato‐onions ( Allium cepa L. var. aggregatum G.Don) is still unclear. This study investigated plant–plant interactions using tomato and four varieties of potato‐onion. A comparative analysis was conducted by establishing multiple cultivation systems, including tomato monoculture, intraspecific (tomato/tomato), and interspecific (tomato/potato‐onion) combinations. When neighbored by “Ningan” or “Qitaihe” potato‐onions, tomato roots overgrew into the neighbor's zone, resulting solely in a significant increase in tomato root biomass. In contrast, neighbored by “Suihua” or “Wuchang” potato‐onions, tomato roots avoided competition while the potato‐onion roots grew into tomato territory. This mode significantly increased tomato plant height, shoot biomass, root biomass, whole plant biomass, root length, and plant nitrogen, phosphorus, and potassium content. The relative interaction index (RII) confirmed that “Suihua” and “Wuchang” potato‐onions promoted tomato growth, whereas “Ningan” and “Qitaihe” had no significant promoting effect, and intraspecific tomato competition was inhibitory. Correlation analysis further revealed that horizontal asymmetry in root biomass was significantly negatively correlated with plant height, shoot biomass, nutrient contents, and RII, whereas most other growth‐related traits showed significant positive correlations among themselves. Our findings provide a theoretical foundation for understanding interspecific plant interactions and optimizing tomato/potato‐onion intercropping systems using selected potato‐onion varieties.