Field Evaluation for Cool‐Tolerance in Grain Sorghum1

Abstract

Sorghum [Sorghum bicolor (L.) Moench] may be injured at low nonfreezing temperatures. Therefore, there is interest in identifying genetic material which can tolerate cooler temperatures. The objectives of this research were to develop a procedure that quantitated the developmental rate of sorghum under cool nighttime temperatures and to determine if genetic variation existed for this trait. A developmental index (DI), based on relative heat units to 50% anthesis for each genotype grown in two environments, was used. One environment had a high nighttime temperature while the other had a low nighttime temperature. Developmental index values obtained were positive, negative, or zero. Genotypes with positive DI values maintained their developmental rate relatively better under cooler nighttime temperatures and were considered cool‐tolerant. Results showed that lines and hybrids from Canada or the northern USA generally had positive DI values. Lines selected in the environment with the high nighttime temperatures (seasonal average 14 C) generally had negative DI values, whereas, lines selected in the environment with the low nighttime temperatures (seasonal average 8 C) generally had positive DI values. Parent lines identified as cool‐tolerant tended to pass the trait to their progeny. Maturity among these genotypes seemed to be independent of the DI value for that genotype. Days to 50% anthesis for these genotypes ranged from 50 to 72 days. This DI appeared to quantitate the ability of a sorghum genotype to maintain a relative developmental rate under cooler nighttime temperatures and there seemed to be substantial genetic variation for the trait this index measures. This DI should be useful in quantifying this trait for further experimentation and for selection in breeder's nurseries.