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Selection Response and Developmental Basis for Early and Late Panicle Emergence in Alamo Switchgrass

Dep. of Crop Science, North Carolina State Univ., Box 8604, Raleigh, NC 27695-8604
Soil and Crop Sciences Dep., Texas A&M Univ., College Station, TX 77843-2474
USDA-ARS Pasture Systems and Watershed Management Res. Lab., Curtin Road, University Park, PA 16802-3702

^* Corresponding author (GVANESBR{at}cropserv1.cropsci.ncsu.edu).

For many determinate crop species, delayed flowering, associated with the production of more mainstem leaves and/or a reduced rate of leaf appearance, extends the vegetative phase and results in higher biomass yields. Studies were carried out on ‘Alamo’ switchgrass (Panicum virgatum L.), a potential biofuel crop, to determine the realized heritability and developmental basis for variation in the time to panicle emergence. A single cycle of divergent selection for time of panicle emergence (earliest and latest 3%) was carried out. Time panicle emergence for the parent and progeny generation was evaluated in the field for 2 yr and 1 yr in a greenhouse trial. For the parental generation, leaf emergence was monitored weekly and final leaf numbers were recorded. Panicle emergence for the selected early and late parents differed by an average of 22 d (10 d earlier and 12 d later than the original population). Realized heritabilities in the year following establishment were 1.0 and 0.92 for early and late panicle emergence, respectively. The early and late parent plants initiated growth at the same time in spring and produced leaves at the same rate; however, late plants produced from 0.7 to 2.1 more mainstem leaves than early plants. Similar leaf appearance rates, combined with higher final leaf numbers on late than on early plants, strongly suggested that late panicle emergence resulted from delayed floral initiation. This study showed that there is considerable genetic variation for flowering time in Alamo switchgrass and that the extended period of vegetative growth in late flowering types was associated with the production of more leaves.

Received for publication March 11, 1997.

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