QTL analysis of regrowth ability in bmr sorghum (Sorghum bicolor [L.] Moench) × sudangrass (S. bicolor subsp. drummondii) populations

Sorghum (Sorghum bicolor [L.] Moench) is an important annual forage crop. Multiple harvests per year not only increase the total yield of sorghum but also help to avoid its injury and damage by biotic and abiotic stresses. It is well known that S. bicolor subsp. drummondii, or sudangrass, regrows vigorously after cutting. To elucidate the genetic mechanisms underlying this ability, we evaluated recombinant inbred lines and advanced populations of bmr (brown midrib) sorghum × sudangrass under different environments and identified quantitative trait loci (QTLs) controlling regrowth ability. Although the dry matter weight at the second harvest varied among years, significant QTLs for increased regrowth ability were detected on chromosomes (Chrs.) 3, 6, 7 and 10. In particular, the sudangrass alleles of two QTLs detected on Chrs. 7 and 10 showed a positive effect on regrowth ability. We named the QTL on the short arm of Chr. 7 qRG7-1 and verified it in the QTL analysis of F₃ and BC₂F₃ populations. QTL analysis by using an F₃ population segregating for regrowth ability also showed a clear LOD peak in the qRG7-1 region. Substitution mapping using two BC₂F₃ populations placed qRG7-1 at 3.81–9.75 Mb on Chr. 7.