The GEM breeding populations CUBA164:S1517 and CUBA117:S1520 have shown promise as high-yielding and nutritious silage source populations for developing inbreds. We developed 114 S2 (CUBA164:S1517) and 55 S4 (CUBA117:S1520) families, and in 2003 these were evaluated for silage potential as topcrosses to inbred LH279. Twenty superior S2 families identified in the topcross evaluation were recombined in summer of 2004 to form an improved breeding population designated the GEM Quality Synthetic (GQS C0) that will undergo S2-topcross recurrent selection. (See field trials from 2003: CUBA – Forage yield evaluation and CUBA – Nutritional evaluation.) Superior inbred families will also be further inbred and crossed to several non-Stiff Stalk tester inbreds to identify inbreds suitable for release. GQS will complement the Wisconsin Quality Synthetic (WQS, a non-Stiff Stalk population, that has undergone three cycles of S2-topcross selection using B73-type tester inbreds.
The first cycle of S2-testcross selection began in 2004. We produced 200 new S1 families during the winter. These S1 families were visually screened under stress conditions (early planting, high plant density and disease pressure), and 73 were crossed to W604S during the winter of 2005/6. The testcrosses were evaluated for yield and quality in 2006 in trial GQS604S. The best families (20) were recombined in the summer of 2007 to create GQS C1.
The second cycle of the GQS population was started in 2008. During the winter nursery of 2007-08, 20 GQS half-sib families derived from the intermating process conducted in summer 2007 were selfed. At least 10 self-pollinations were conducted for each of the half-sib families. Ten S1 families were derived from each of the 20 half sib families. A total of 200 S1 families were planted in our summer nursery in 2008 and approximately half of them were eliminated based on agronomic appearance. Two ears were harvested from each of the selected S1 families producing a total of 200 S2 lines. Those lines were crossed by W604S during 2009 summer nursery. A set of 201 GQS C1 derived S2 lines crosses were evaluated at two locations (West Madison and Arlington) in 2010 with two replications per location in trial GQS C1 S2. The best 20 S2 lines were identified from this evaluation and will be recombined in summer nursery 2011 to create GQS C2. (See field trials from 2010: GQS C1 S2 – Forage yield evaluation and GQS C1 S2 – Forage quality evaluation.)