Noncanonical Strigolactone Analogues Highlight Selectivity for Stimulating Germination in Two Populations.

Strigolactones (SLs) are plant hormones exuded in the rhizosphere with a signaling role for the development of arbuscular mycorrhizal (AM) fungi and as stimulants of seed germination of the parasitic weeds , , and , the most threatening weeds of major crops worldwide. is present mainly on rape, hemp, and tobacco in France. 2a preferentially attacks hemp, while 1 attacks rapeseed. The recently isolated cannalactone () from hemp root exudates has been characterized as a noncanonical SL that selectively stimulates the germination of 2a seeds in comparison with 1. In the present work, (-)-solanacol (), a canonical orobanchol-type SL exuded by tobacco and tomato, was established to possess a remarkable selective germination stimulant activity for 2a seeds. Two cannalactone analogues, named (±)-SdL19 and (±)-SdL118, have been synthesized. They have an unsaturated acyclic carbon chain with a tertiary hydroxy group and a methyl or a cyclopropyl group instead of a cyclohexane A-ring, respectively. (±)-SdL analogues are able to selectively stimulate 2a, revealing that these minimal structural elements are key for this selective bioactivity. In addition, (±)-SdL19 is able to inhibit shoot branching in and and induces hyphal branching in the AM fungus , like SLs.