Methods of simulating freezing damage during sorghum grain fill

Sorghum [Sorghum bicolor (L.) Moench] grain yields can be reduced if plants are exposed to freezing temperatures prior to reaching physiological matur ity, Two field experiments were conducted to evaluate chemical desiccation and panicle removal as methods for simulating the loss of carbohydrate prod uction associated with leaf death or transport tissue damage when sorghum i s exposed to freezing temperatures during grain fill. In one experiment, bo th treatments were repeated at 3- to 4-d intervals during grain fill with a range of hybrid maturities and environments to establish a relationship be tween caryopsis weight or test weight with heat unit accumulation after ant hesis. This relationship was best described as sigmoidal in shape. A second field experiment compared these two treatments with potted held-grown plan ts exposed to -2 degrees C for 4 h. Treatments were applied four different times during grain fill. Panicle removal produced caryopsis weights 5% grea ter than those from freeze treatments, whereas chemical desiccation resulte d in caryopsis weights 13% greater than those from freeze treatments. Test weights followed similar trends. Caryopsis weights from each treatment were similar across experiments. Panicle removal accurately simulated caryopsis weight reductions caused by exposure to freezing temperatures throughout t he grain-filling period, Chemical desiccation underestimated freeze damage during early grain fill but adequately simulated caryopsis reductions durin g late grain fill. Test weights from panicle removal treatments were simila r in both experiments, while chemical desiccation was inconsistent across e xperiments. Test weight reductions caused by exposure to freezing temperatu res were not adequately simulated by either treatment, The results of these experiments indicate that panicle removal is a more appropriate method for simulating freeze damage to maturing grain sorghum than is chemical desicc ation; how-ever, chemical desiccation may be utilized if appropriate adjust ments are made during early grain fill.