A Simple System for Promoting Flowering of Switchgrass In the Greenhouse.

In switchgrass (Panicum virgatum), the transition from vegetative to reproductive development has been shown to be a photoperiod mediated process.  With its extensive native range, photoperiod response varies widely within the species.  In order to synchronize flowering among cultivars of distinct origin, disparities in light-driven developmental responses often require breeders to develop elaborate photoperiod regiments.  The objective of this research was to identify a simple photoperiod treatment that could be used to incur reproductive development for three upland cultivars of switchgrass: Cave-In-Rock (origin 37⁰N), Sunburst (origin 42⁰N), and Dacotah (origin 46⁰N).  Several genotypes of each cultivar were removed from the field, potted, and then grown in either 24-hr low irradiance daylight-extended photoperiod (continuous) or under ambient light consisting of both short (<12-hrs) and long (>12-hrs) photoperiods.  In general, the upland switchgrass cultivars reached both heading and anthesis more successfully when grown in continuous light than when grown in a short photoperiod.  Additionally, switchgrass grown in a continuous photoperiod successfully flowered more frequently than those grown under decreasing ambient photoperiod.  On average, switchgrass grown under 24-hr extended photoperiod reached anthesis approximately 20 days earlier (p<0.0001) than those grown under ambient light conditions outside.  In addition, switchgrass grown under 24-hr light flowered approximately six days longer than those grown under ambient light in the GH.  In summary, the flowering processes in these three northern upland switchgrass cultivars are not particularly sensitive to photoperiod. They will be induced to flower under 24-hr low irradiance daylight-extended photoperiod in both increasing and decreasing day lengths.  These results identify a simple system that uses inexpensive equipment (common fluorescent bulbs) and requires no alternating light and dark periods to promote panicle production in switchgrass.  This system will be useful for improving seed yield components, via controlled pollination.