CANOPY ARCHITECTURE AND MORPHOLOGY OF SWITCHGRASS POPULATIONS DIFFERING IN FORAGE YIELD

Phenotypic selection has been used to improve forage yield and in vitr o dry matter disappearance (IVDMD), but the effects on canopy architec ture and morphology are not understood. Our objectives were to determi ne if canopy architecture and morphology can explain genotype x enviro nment (G x E) yield differences in switchgrass (Panicum virgatum L.) a nd to evaluate canopy architecture and morphology as selection criteri a for increasing yield. This study was conducted in 1993 near Mead, NE , and near Ames, IA. The experimental design was a randomized complete block experiment with a split-plot arrangement of four replicates at each location. Whole plots were tiller population and subplots were sw ard maturity. Tiller populations were harvested on 9 June, 19 July, an d 27 August at Ames and on 10 June, 27 July, and 26 August at Mead and were classified morphologically. Tillers were separated into primary yield components and dried at 55 degrees C to determine total forage y ield and dry matter contribution of morphological components. Genotype x environment interactions occurred for total forage yield and tiller density. Previous phenotypic selection for increased forage yield and IVDMD apparently altered morphological changes within the canopy of s elected switchgrass populations. The most apparent changes were develo pment of additional collared leaves and internodes in some populations across locations. Although canopy architecture may not be a useful se lection criterion because of variability associated with individual ca nopy traits, indirect measurements showed that leaf area index (LAI) h as some potential as a selection criterion for increasing total forage yield. However, selection for individual canopy traits may be most ef fective for modifying sward growth habits.