Effect of Early and Mid-Season Cold Temperature Stress On Growth, Phenology and Yield Components of Sorghum.

Cold temperature during early and mid-growing season is a common abiotic constraint to grain sorghum production in Kansas. The objective of this study was to investigate the effect of this stress on growth, phenology and yield components of sorghum. Two sets of experiments, experiment I for early-season stress and experiment II for mid-season stress, were carried out in the greenhouse and growth chambers using three sorghum genotypes with contrasting response to cold temperature stress, Shan Qui Red (early-season cold tolerant), SRN39 (cold susceptible line) and Pioneer 84G62 (unknown).  A split-plot design with three replications was used in both experiments with temperature regimes treated as main-plots and genotypes as sub-plots. The temperature treatments were imposed by keeping plants in a growth chamber calibrated to 15/13ºC (day/night) for cold treatment and 25/23ºC (day/night) for normal temperature and the treatments lasted 10 d for both experiments. The experiments were repeated three times. Seedling height, vigor and dry weight,  number of leaves per plant, leaf chlorophyll content, days to flowering, anthesis duration, days to maturity, panicle weight, number of seeds per panicle, thousand kernel weight (TKW) and total seed weight per panicle were measured. Early-season cold temperature significantly reduced seedling height, vigor and dry weight, leaf chlorophyll content and delayed flowering and maturity, but had no effect on final leaf number, and plant height. While mid-season stress prolonged anthesis duration, delayed maturity and reduced all yield components. The results indicate that early-season stress has less effect on final yield provided that germination is not critical. Cold temperature stress at flowering seems to negatively interfere with pollination and seed setting resulting in significant yield reduction.