First step from an arable weed to a honey crop: Breaking seed dormancy of Stachys annua

Stachys annua – a typical annual weed species in stubble fields – was the most important melliferous plant in the Carpathian Basin during the 19th century. The agricultural intensification led to a drastic decline for the species, and previous efforts for its cultivation were unsuccessful due to its unevenly germinating seeds. The objective of this study is to identify an effective method for overcoming the primary seed dormancy of S. annua. In laboratory experiments we evaluated the effects of moist stratification for 4 weeks (in cold / warm sand) as well as application of gibberellic acid (GA3) solution (250 mg/L) on seed germination under two light-temperature regimes (a “constant” regime at 20 °C in continuous darkness, and a “fluctuating” regime with 14 h light at 20 °C followed by 10 h dark at 10 °C). The trial started with freshly matured and harvested seed lots, and the samples were germinated on filter papers soaked with the selected solution (distilled water, DW or gibberellic acid, GA3) in incubation chambers. Our results indicate that freshly matured seeds were mostly dormant at maturity. Gibberellins play a crucial role in breaking seed dormancy and can help substitute for the cold requirement. The best combination consisted of a GA3 treatment following a short (4 weeks) warm stratification, which led to a high (98%) germination rate in darkness at 20 °C. The results suggest that in nature, the seeds of S. annua require a longer period for their primary dormancy to be released. Our findings can establish the basis for the development of dormancy-breaking technology to achieve a uniform germination allowing its future cultivation in bee gardens and arable fields.