Benzoxazinoid Induction and Secretion in Wheat by Intercropped Faba Bean: Cross-Plant Transfer, Environmental Degradation and Limited Negative Impact on Growth

Abstract

Benzoxazinoids (BXs) synthesised by cereal plants are vital for stress resistance. However, information regarding the induction of specific BXs (DIBOA, DIMBOA, and MBOA) in wheat by typical cereal-legume intercropping systems, such as wheat/faba bean, and their effects on neighbouring intercropping crops, remains limited. To address this knowledge gap, pot and field planting experiments were conducted to examine the influence of intercropped faba bean (IF) on the synthesis and secretion of BXs in wheat, their subsequent absorption by faba bean, and their impact on plant growth. Results showed that under both planting conditions, IF could induce an increase in the concentration of BXs in the shoots (leaves and stems) and underground (roots) parts of intercropped wheat (IW), as well as in the rhizosphere soil (p < 0.05), with the highest concentration in the leaves, reaching up to 78.0 μg/g. The concentration of BXs in various organs of IW was higher under field conditions than under potted conditions, and showed a pattern of leaves > roots > stems > rhizosphere. DIMBOA, induced to synthesise and secrete in the wheat rhizosphere, underwent accelerated degradation and reduced half-life due to the soil environment, which is rich in diverse microorganisms and organic residues. In addition, compared to monoculture faba bean (MF) with trace levels of BXs, all three BXs types were detected in the rhizosphere, roots, and shoots of IF, and all significantly increased (p < 0.05). The BXs absorbed by IF exhibited varying degrees of negative correlation with the growth parameters of wheat and faba bean, but the negative impact on growth was limited. In summary, our research findings enhance the understanding of the secretion of BXs induced by legume crops in cereal-legume intercropping systems and their absorption in interspecific interactions among legume crops.