Allelopathic effect of fibre hemp (Cannabis sativa L.) on monocot and dicot plant species

• The studies examined the allelopathic effects of Cannabis sativa L on monocot (wheat, rye) and dicot (lupine, rape) crop species.
• Hemp extract (HE) decreased the germination of monocots. For rape germination the hormesis effect was observed.
• Higher amount of HE disturbed growth of rape and disorders in lupine seedlings growth, roots elongation and gravitropism.
• The increasing extract concentration resulted in species specific increase of wheat seminal root number.
• HE caused molecular response in lupine roots by increasing the transcription of the isoflavonoids synthesis pathway genes.

The studies examined the effects of water extracts of fibre hemp (Cannabis sativa L.) on germination energy and rate of monocot: spring wheat (Triticum aestivum ssp. vulgare L.), winter rye (Secale cereale L.) and dicot: yellow lupine (Lupinus luteus L.), winter rape (Brassica napus ssp. oleifera L.) crop species. Hemp is an effective weeds suppressing crop plant, but the nature of its domination and the influence on the following crops is not fully understood. In the experiments the hemp extract was applied in 0.1, 0.5, 2.5 and 10% concentrations and water was used as a control. The germination was observed daily and after 7 days plants were harvested and the number, length and weight of roots and leaves was measured. For yellow lupine the influence of hemp extract on the expression of the isoflavonoids synthesis pathway genes was studied in 4 day old seedlings. Hemp extract decreased germination rate of monocot plants while on rape the effect was concentration dependent. High concentrations (2.5 and 10%) reduced the germination rate while low were stimulatory. Lupine seeds germinated well but on high concentrations after 4 days seedlings decayed or showed poor growth and abnormal gravitropism. The number of the seminal root of wheat seedlings correlated with hemp extract concentration and increased from 4.7 (at 0%) to 6 (at 10% extract). All four species produced shorter roots on the highest concentration and oilseed rape also on 2.5% extract. Time and concentration dependent increase of lupine chalcone synthase and isoflavone synthase transcription indicated the defensive response mechanism on allelopathic activity of hemp extract.