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FORAGE & GRAZING LANDS

Variation between Alamo and Cave-in-Rock Switchgrass in Response to Photoperiod Extension

^a M.A. Husse, Dep. of Soil and Crop Sciences Texas A&M University, College Station TX, 77843-2474
^b USDA-ARS, Pasture Systems and Watershed Management Research Unit, Building 3702, Curtin Road, University Park, PA 16802-3702

^* Corresponding author (mas44{at}psu.edu)

The length of the growing period for switchgrass (Panicum virgatum L.) can vary considerably across environments. For many species, phenotypic plasticity for length of the vegetative phase results from a photoperiod mediated transition from vegetative to reproductive development. The objective of this study was to determine the effects of photoperiod on tiller development on a northern (Cave-in-Rock) and southern (Alamo) switchgrass cultivar. Plants were removed from the field and grown in greenhouses during winter at natural (11.5–13 h) and extended (16 h; 12 h natural + 4 h light extension) photoperiods. Photoperiod extension was with 100 µmol m^-2 s^-1 of photosynthetic photon flux density. For Cave-in-Rock at a 16-h photoperiod, panicle emergence was delayed by 18 d (39% longer than at the 12-h photoperiod) and the duration of panicle exsertion was extended by 17 d (243% longer than at the 12-h photoperiod). The delay in panicle emergence for Cave-in-Rock was associated with an increase in the phyllochron, whereas the total number of leaves on a tiller was not affected. Extended photoperiod did not alter time to panicle emergence in Alamo; however, the duration of panicle exsertion was extended by 15 d (136%). A delay in development under long photoperiods in both cultivars suggested a facultative short-day response; however, photoperiod did not appear to affect the initiation of reproductive development but rather extended the period of panicle exsertion. Photoperiod has a large effect on growth and development of switchgrass cultivars affecting their forage or biomass production value. Forage production of switchgrass in short-day environments may be improved with cultivars that are less photoperiod sensitive.