Quantification of Heat Stress Effects on Grain Formation in Maize.

Maize is an important food crop throughout the world. Rising temperatures due to global climate change are more likely to be above the optimum for maize for longer periods of time. High temperatures increase development rates and respiration and may result in lower grain yields in tropical and temperate growing areas than in the past. Crop models are being used to assess the effects of temperature on grain yield in maize but there is little quantitative information on superoptimal temperatures and grain yield. We carried out a study using six outdoor sunlit growth chambers to quantify the effects of heat stress on grain formation. The studies were carried out over two growing seasons to assess the effects of 12 temperatures (16 to 35C) on grain formation. The temperature treatments were applied after pollination which was done by hand. Optimum temperature for grain yield was about 24C with grain yield per plant decreasing rapidly at higher temperatures. At the highest average temperature of 35C, grain yield was reduced by about 80% relative to the optimum. Algorithms were developed from the data and applied in the maize model MAIZSIM.