Variation between Alamo and cave-in-rock switchgrass in response to photoperiod extension
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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 mol 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.
