The structure-activity relationship of aryloxyacetylthioureas for the inhibition of Orobanche minor radicle elongation.

Orobanchaceae root parasitic weeds cause significant damage to agriculture and become threats to global food security. Integrated pest management is a key concept in modern agriculture and requires chemicals with various modes of action. Planteose accumulates as a storage carbohydrate in the dry seeds of root parasitic weeds. In Orobanche minor seeds, planteose is hydrolyzed by an α-galactosidase, OmAGAL2, during germination. It was found that the OmAGAL2 inhibitor, PI-28, suppressed the radicle elongation of germinating O. minor seeds. This inhibitory activity against O. minor radicle elongation was evaluated for a series of aryloxyacetylthioureas synthesized based on the structure of PI-28. Compounds with a 3-Cl or 4-Cl substituent on the benzene ring in the phenoxy moiety in PI-28 exhibited more potent activity than the parent PI-28. This is the first report on the effect of aryloxyacetylthioureas on a root parasitic weed and will contribute to the development of control reagents for root parasitic weeds.