Abstract The demand for cereal rye ( Secale cereale L.) as a cover crop is rising in organic and conventional farming systems due to its benefits to soil conservation and health as well as for weed suppression. Cereal rye produces allelochemicals that reduce weed emergence and growth. However, breeding programs for cover cropping have focused on biomass production, and little attention has been paid to breeding for increased allelopathy. In this study, 38 crosses derived from lines previously identified as highly allelopathic accessions and commercial cereal rye varieties ND Gardner and Aroostook were screened for allelopathic activity using the in vitro, equal‐compartment‐agar method with lettuce as the bioindicator. After in vitro phenotyping, allelopathic activity was also assessed in a loam soil under greenhouse conditions. Lettuce growth suppression was used as a surrogate of weed suppression, and vegetative growth of lettuce was characterized. Fourteen lines demonstrated high allelopathic activity causing >50% lettuce growth reduction. In vitro, broad‐sense heritability ( H ) estimates were 0.82 and 0.57, for lettuce injury and root reduction, respectively. In soil, H for lettuce injury 7 days after planting and shoot biomass reduction was 0.17 and 0, respectively. Cereal rye allelopathic activity in vitro was strongly genetically correlated ( r G = 0.73–0.94) with plant height, leaf area, tiller number, and dry biomass. The H estimates in vitro indicate that allelopathy has a genetic component large enough to justify breeding for increased allelopathy in cereal rye, and that vegetative growth traits can be part of the selection criteria for this trait.
Jackson et al. (2026) studied this question.