Sand verbenas (Abronia spp., Nyctaginaceae) germinate in response to ethylene

Sand verbenas (Abronia spp., Nyctaginaceae) are difficult to germinate in the laboratory. This hinders conservation and restoration efforts for Abronia spp. some of which are rare and others of which have been displaced from dune environments by invasive species and human activities. The possibility that ethylene (supplied as the liquid ethephon) could promote germination was investigated for Abronia fragrans, Abronia maritima, Abronia umbellata, and Abronia villosa. Germination of achenes from which the anthocarp had been removed ranged from 0% to 15% in deionized water and at alternating temperatures of 27/20 °C associated with a 12-h light/12-h dark cycle. For A. maritima and A. umbellata under similar conditions of temperature and light, germination exceeded 90% for all concentrations of ethephon tested (10, 100, and 500 μ mol l−1). The rate of germination was highest at 500 μ mol l−1; however, the radicles were stunted at this concentration. Germination was also promoted by imbibition of the achenes with ripe apple tissue providing evidence that the ethephon effects are due to ethylene. Ethephon treatment (100 μ mol l −1) also significantly increased germination for A. fragrans and A. villosa suggesting that the different species of sand verbena may have similar dormancy mechanisms.