Excessive crown node elevation of warm-season grass seedlings is a major limitation to successful establishment. Crown node placement at or above the soil surface limits the opportunity for adventitious root development at the crown node. KJeingrass (Panicum coloratupt L.) and switchgrass (Panicum virgatum L.) germplasm with low-(LC) and elevated-(EC)crownnodeplacement[at 1.5umolm-2S-lphotosynthetic
photon flux density (PPFD)] were evaluated for crown node elevation (above soil surface) and coleoptile (or shoot) length under continuous low PPFD ranging from 0 (complete darkness) to 26.8 p,mol m? S~l in a growth box. The objective of this research was to characterize the differences in photomorphogenic responses of emerging seedlings of the selected and nonselected populations. In darkness, coleoptiles of LC seedlings were longer than coleoptiles of EC seedlings, while crown node elevation was higher for EC than LC. The PPFD required to prevent crown node elevation in kleingrass was about 5, 30. and> > 30 p,mol m-2 sol (beyond our level of testing) for LC, nonselected, and EC, respectively. For switcbgrass, the PPFD thresholds were lower. To prevent crown node elevation in switchgrass,
about 1.6, 5, and 15 umol m-2 S-l PPFD were required for LC, nonselected, and EC, respectively. The LC germplasm of both species exhibits a lower PPFD threshold for de-etiolation, greater coleoptile length, and a decreased rate of mesocotyl elongation than EC germplasm.
The populations selected for LC node placement are hypothesized
to have increased establishment success, especially in conditions where low PPFD levels reach the emerging seedling.