An Ideotype for Selection Among F1 Half-Sibs of Switchgrass.

Switchgrass, Panicum virgatum, is important as both a forage crop and, more recently, as a biofuel crop.  Breeding for increased yield and disease resistance would benefit switchgrass production in both capacities.  The objective of this study was to determine a breeding ideotype for early selection of high yield and rust disease resistance.  A polycross nursery was established using 14 clonal propagules from each of three plant introductions from Arkansas, Florida, and Texas, an experimental line from Oklahoma, and the cultivar Cimarron.  Seed were collected from each parent clone and used to establish a F1 half-sib nursery composed of 5 families with 14 sub-families per family and 10 replications per sub-family.  The year following establishment, the following traits were measured and recorded: plant height, tiller count, stem diameter, leaf width, leaf angle, color, bloom, rust severity, and yield.  Traits were measured in June with the exception of yield, which was measured in October, and rust severity, which was measured once a month in June, July, August, and October.  JMP (v. 8.0, SAS) was used to calculate correlations between measured traits and yield or disease severity in order to assess the potential of these traits as early selection indicators for high yielding, disease resistant plants.  Yield showed significant (p<0.001) positive correlations with tiller number (r =0.77), plant height (r =0.51), and stem diameter (r =0.35), and significant negative correlations with leaf angle (r =-0.28).  Rust disease ratings in June and July showed signficant negative correlations with color (r =-0.36, -0.29) and bloom (r = -0.23, -0.22), with less disease associated with plants having blue leaves with a visible waxy bloom.  These results suggest potential improvement in yield and disease resistance by selecting for an ideotype composed of tall plants with drooping, blue leaves, visible bloom, high early tiller numbers with larger stem diameter.