Non-Flowering Sorghum Spp. Hybrids: Perennial, Sterile, High-Biomass Feedstocks.

Perennial Sorghum spp. hybrids such as Columbusgrass (Sorghum almum Parodi; S. bicolor [L.] Moench  x  S. halepense [L.] Pers.) and the reciprocal hybridization (S. halepense  x  S. bicolor; e.g. Cv 'Krish') are high-biomass forage feedstocks.  Utilization of such hybrids is limited, however, by both their short-term persistence and tendency to produce significant quantities of seed which can become weed banks in subsequent crops.  Natural Columbusgrass hybrids occur throughout annual sorghum production zones, but natural reciprocal hybrids have not been well characterized.  The objective of this study was to collect and evaluate natural Sorghum spp. hybrids for utility as improved forage feedstocks.  A total of 29 putative hybrid accessions were collected between 1 October and 20 November 2009 based on delayed flowering and increased plant height compared to neighboring Johnsongrass populations.  Six accessions failed to initiate flowering in 2009 and have subsequently remained non-flowering in field, greenhouse, and growth chamber environments.  Flow cytometry confirmed tetraploidy (2n=4x=40) in all six accessions, and DNA marker screens utilizing 350 EST-SSRs confirmed them to be Sorghum spp. hybrids.  Preliminary biomass yields for the largest accession (09TX15) averaged 12 dry tons per acre in a 130 day season.  The utility of such non-flowering Sorghum spp. hybrids as perennial forage feedstocks, potential biomass gains in two-harvest hay systems, and their value towards developing environmentally-benign, perennial sorghum feedstocks will be discussed.