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

Abstract

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.