Phenotyping a Diverse Collection of Forage Sorghum Genotypes for Chilling Tolerance

Forage sorghum (FS) (Sorghum bicolor (L.) Moench) is a warm-season biomass crop used as forage for hay or silage with the potential to become a bioenergy feedstock or for dual-purpose (forage and energy). The objective of this study was to screen potential forage sorghum genotypes for increased chilling tolerance and biomass productivity. Seventy-one genotypes of FS were first ranked for high to low vigor index under controlled conditions at 24, 12, and 10 °C. Field experiments were also conducted on a subset of 12 genotypes in Fargo and Hickson, ND, USA, in 2017 and 2018, using two different seeding dates: early (10 May) and late (27 May). Field emergence index values were greater for the late-seeding compared with the early seeding date. Under field conditions, seed mortality and biomass yield were affected by the seeding date and biomass yield correlated with emergence index and normalized vegetative index. Chemical composition of forage sorghum biomass was not affected by the seeding dates. The results of this study suggest that some forage sorghum genotypes carry genetic traits for increased chilling tolerance and produce greater biomass yield when seeded earlier than normal, which could allow for breeding chilling tolerance into forage sorghum.