Cold Temperature Episode at Seedling and Flowering Stages Reduces Growth and Yield Components in Sorghum

Cold temperature is one of the major abiotic constraints to sorghum [Sorghum bicolor (L.) Moench] production in the United States. Though the effect on germination and establishment are well documented, the impact of the stress on adult plant traits is not known. The objectives of this study were to investigate the impact of cold temperature at two growth stages and identify genetic sources of tolerance for use in breeding programs. Three genotypes, Shan Qui Red (tolerant), SRN39 (susceptible), and Pioneer 84G62, were subjected to two temperature regimes, cold temperature [15°C (day) and 13°C (night)] and control temperature [25°C (day) and 23°C (night)], at seedling and flowering stages using growth chambers, and the stresses lasted 10 d. Another 136 accessions were evaluated in the field under cold and control temperatures imposed by varying planting dates. Data were collected on emergence, seedling growth parameters, phenology, and yield components. Early season cold stress reduced seedling vigor (3.4 vs. 1.2) and leaf chlorophyll content (28.83 vs. 36.59) and delayed flowering and maturity by 8 and 4 d, respectively, but had no effect on yield components and plant height. Stress at flowering stage delayed maturity by 9 d and significantly reduced all yield components. The effect of cold stress at seedling stage may not be critical to yield provided that emergence is not affected. Stress at flowering, however, may be detrimental and the effects seem irreversible.