CHARACTERIZATION OF CROWN NODE ELEVATION IN PANICOID GRASSES

In Panicoid grasses, elevation of the crown node above the soil surfac e caused by excessive subcoleoptile internode elongation is detrimenta l to seedling establishment. We describe a technique to screen grass s eedlings for excessive crown node elevation. Seed of 11 perennial gras s cultivars were germinated and grown in a plywood box 1.2 X 1.2 X 1.2 m at an irradiance of 1.5 mumol m-2 sec-1 at 30-degrees-C. A subset o f 8 grasses were grown similarly but at an irradiance of 0.75 mumol m- 2 sec-1. Elevation of crown nodes above the growth media and shoot len gth (from crown node to leaf tip) were measured 7 days after planting. The crown nodes of 4 Eragrostis species were not elevated above the s oil surface, while other species had mean crown node elevations of 1 c m or more. Relative ranking of crown node elevation was similar for a species within each light level, but response to change in light inten sity was not consistent across species. Sideoats grama (Bouteloua curt ipendula (Michx.) Torr.), blue grama (Bouteloua gracilis (H.B.K. Lag. ex Steud.)), and kleingrass (Panicum coloratum L.) exhibited significa nt crown node elevation in this system. Estimates of genetic variation based on comparison of apomictic and sexual grasses within this group suggest that substantial genetic variation exists for excessive subco leoptile internode elongation and that progress by selection for lower crown node placement should be possible in most of the grasses studie d. This system allows characterization of grasses for extent of crown node elevation and is being used in a recurrent selection protocol to select for lower crown node placement.