CROWN NODE ELEVATION OF SWITCHGRASS AND KLEINGRASS UNDER LOW-LIGHT

Excessive crown node elevation of warm-season grass seedlings is a maj or limitation to successful establishment. Crown node placement at or above the soil surface limits the opportunity for adventitious root de velopment at the crown node, Kleingrass (Panicum coloratum L.) and swi tchgrass (Panicum virgatum L.) germplasm with low- (LC) and elevated- (EC) crown node placement [at 1.5 mu mol m(-2) s(-1) photosynthetic ph oton flux density (PPFD)]were evaluated for crown node elevation (abov e soil surface) and coleoptile (or shoot) length under continuous low PPFD ranging from 0 (complete darkness) to 26.8 mu mol m(-1) s(-1) in a growth box. The objective of this research was to characterize the d ifferences in photomorphogenic responses of emerging seedlings of the selected and nonselected populations. In darkness, coleoptiles of LC s eedlings were longer than coleoptiles of EC seedlings, while crown nod e elevation mas higher for EC than LC. The PPFD required to prevent cr own node elevation in kleingrass was about 5, 30, and >> 30 mu mol m(- 2) s(-1) (beyond our level of testing) fur LC, nonselected, and EC, re spectively. For switchgrass, the PPFD thresholds were lower, To preven t crown node elevation in switchgrass, about 1.6, 5, and 15 mu mol m(- 2) s(-1) PPFD were required for LC, nonselected, and EC, respectively. The LC germplasm of both species exhibits a lower PPFD threshold for de-etiolalion, greater coleoptile length, and a decreased rate of meso cotyl elongation than EC germplasm, The populations selected for LC no de placement are hypothesized to have increased establishment success, especially in conditions where low PPFD levels reach the emerging see dling.