| Coreopsis is Florida’s state native wildflower, and the Florida Department of Transportation adopted it for roadside revegetation. However, C. floridana and C. lanceolata seeds have dormancy that can impede economic establishment of sustainable populations. Coreopsis seeds (achenes) consist of a pericarp, testa and endosperm surrounding a dicotyledonous embryo. In C. lanceolata , lateral endosperm was a single cell-layer, but 1 to 3 cell-layers at the micropylar end, while in C. floridana a single cell-layer persisted throughout. Endosperm ploidy was 1.5 times that of embryo, consistent with angiosperms. Endosperm removal alleviated dormancy in dark-imbibed C. floridana seeds, while in both species, excision of the same tissue permitted germination at supraoptimal temperatures. Optimum germination temperatures in Coreopsis were 15 and 20°C, and germination declined above 25°C. In C. lanceolata, endo-β-mannanase (EBM) activity was detected at 90 hours imbibition but C. floridana seeds did not exhibit enzyme activity anytime during germination. There was an association between EBM activity and endosperm rupture. Abscisic acid, tetcyclacis or supraoptimal temperatures inhibited EBM activity and germination.;In 4-week-old C. floridana seeds, pericarp, testa and endosperm imposed dormancy in dark but all naked embryos germinated. Exogenous gibberellic acid (GA) overcame dormancy in dark. Cold (5°C) stratification partially overcame dormancy in dark-imbibed C. floridana seeds, but potassium nitrate was not effective. Four-week-old C. lanceolata seeds required 150 days dry afterripening to overcome dormancy; endosperm enforced dormancy for 90 days, while naked embryos were non-dormant. Potassium nitrate, light and GA did not alleviate dormancy in C. lanceolata , and cold stratification reduced germination.;Osmopriming C. floridana seeds in PEG or PEG+GA improved germination rate and uniformity at 30°C but these treatments were less effective than priming in PEG+6-benzyladenine (BA), which led to 100% germination at 20 or 30°C in dark. When solid matrix priming (SMP) was used, BA gave similar results as in osmopriming, but GA effectiveness improved. In C. lanceolata, osmopriming in PEG+BA increased germination at supraoptimal temperatures.;Dormancy alleviation in Coreopsis was modulated by embryo envelopes. There is great potential for using SMP to enhance germination and improve field establishment in Florida’s native Coreopsis sowing programs. |
