Investigating seed dormancy in switchgrass (Panicum virgatum L.): elucidating the effect of temperature regimes and plant hormones on embryo dormancy.

摘要

Switchgrass (Panicum virgatum L.) is a perennial warm season grass that possesses valuable characteristics as a biofuel crop. Seed dormancy can be a barrier for commercial adoption by negatively impacting stand establishment in the first year. Seed dormancy in switchgrass is classified as non-deep physiological dormancy, where the embryo condition and seed covering tissues may prevent germination. Our lab previously demonstrated that switchgrass seed dormancy was primarily caused by the pericarp/testa, and secondarily by the lemma/palea (bracts). The focus of this research was to explore embryo physiological dormancy and its interaction with environmental cues and surrounding seed layers in five switchgrass varieties with different dormancy levels. Three main objectives were involved: (1) assessing the effect of temperature and light regimes on germination of mature seeds; (2) determining the effect of exogenously applied abscisic acid (ABA), gibberellin (GA), and fluridone (FLU) on germination under either constant or alternate temperatures; and (3) examining the response of physically altered seeds to exogenously applied ABA, GA, and FLU. Incubation of both upland and lowland dormant switchgrass varieties under alternating temperatures (15/30 degrees C) favored germination, while incubation under a constant, warm temperature (30 degrees C) resulted in low percentage germination. In contrast, the low-dormancy cultivar Expresso germinated well at both temperature regimes. Germination in the dark did not differ from an alternating light/dark regime. Exogenous ABA decreased germination in all dormant cultivars studied at both temperature regimes, but the sensitivity of the seeds to ABA was less under alternating temperatures. GA increased germination at a constant temperature in all but one dormant variety. The largest effect of both GA and ABA was observed in seeds with bracts. The promoting effect of FLU on germination was not measured in intact seeds; however, FLU promoted germination at 30 degrees C in seeds with bracts removed, suggesting that the seed covering layers were not permeable to FLU. Collectively, results show that the effect of exogenously applied ABA, GA, and FLU was influenced by temperature, seed covering layers, and seed lot.