Field and Controlled Environments Studies in Sorghum [Sorghum Bicolor (L.) Moench] Lines and Hybrids for Cold Tolerance.

Early season cold tolerance in sorghum can contribute to emergence, seedling establishment, early vegetative growth and reduce damping-off fungal disease infection under chilling conditions. Our objectives were to identify sources of cold tolerance, investigate combining ability and evaluate rapid controlled environment screening techniques. Field studies with two planting dates were conducted in 2009 at Colby, Kansas involving 20 hybrids and 10 parental lines; and in 2011 at Hays and Colby Kansas involving 48 genotypes. Traits measured included emergence percentage, emergence index (EI), shoot biomass (30 days after emergence), leaf number and seed set ratings. All 48 genotypes were also screened for resistance to seedling disease caused by Pythium aphanidermatum and P. irregulare inoculated under warm and cold temperature regimes. Field studies identified four potential lines PI 574586 R/4/KS199B, PI574578 R/KS118 B, PI 574590 R/3/KS118 B and Tx430/SQR-83 with early EI and satisfactory biomass; PI574578 R/KS118 B showed resistance to both Pythium spp; seed quality studies showed that these four lines possessed low tannin content. Significant positive correlation was noticed between EI and biomass in both locations in early planting, suggesting late emerged produces greater biomass compared to early emerged seedling. Field studies conducted in 2009 indicated that general combining ability variance and effects for EI indicated that male parents had greater influence on rate of emergence and female parents on the emergence percentage in hybrid combinations.Greenhouse and growth chamber (15/12^oC day/night) studies evaluated controlled environment screening techniques for EI and shoot biomass, using 18 selected genotypes at Hays and Colby in 2011. Significant correlation between growth chamber and field study for EI indicated that growth chamber screening technique is a rapid and reliable suitable for large breeding population in sorghum. Soil+vermiculate potting mix was more effective for controlled environment screening of shoot biomass, against soil+sand and soil+peat potting mixes.