Propagation by means of embryo excision for endangered clay phacelia ex situ seed production

Abstract

Clay phacelia (Phacelia argillacea N.D. Atwood [Boraginaceae/Hydrophyllaceae]) is an endangered species with seeds that are physiologically dormant and cue-non-responsive. Seed dormancy is a common strategy that is beneficial to species under natural conditions, but working with cue-non-responsive seeds in propagation can be difficult. Several treatment methods are available to artificially break dormancy, but intact clay phacelia seeds of some lots germinate to small percentages or not at all, regardless of the treatment applied. Our work tested micropropagation with embryo excision as a method to artificially break dormancy for seeds that were collected from the 2 known wild populations (Tucker and Railroad). Excised embryos from the Railroad population germinated to 78%, whereas the Tucker embryos germinated to 45%. Both populations suffered more than 50% mortality during acclimatization from in vitro to open air conditions. Survival through vernalization to seed production for acclimatized plants was 100% for Railroad and 88% for Tucker plants. Combining embryo excision with cold stratification, either before or after excision, could potentially improve embryo germination, while modification of conditions during in vitro propagation or acclimatization could improve survival during these critical phases. Individuals that survived to seed production produced an average of >600 seeds after exposure to insect pollinators in a semi-natural outdoor setting. The general protocol described here is not species-specific and provides an alternative seed propagation method for those working with species that have cue-non-responsive seeds.