Abstract
Grain growth in cereal crops is largely dependent on the availability of current photosynthates. Water deficits during flowering and grainfilling limit grain yield partly by reducing the availability of current assimilates. Drought response of breeders lines is often evaluated by screening material in drought prone environments or during the rain-free season by withholding irrigation during the desired treatment periods. The former approach is time consuming due to the erratic nature of drought patterns. In the latter approach, temperatures and daylength during the dry periods often affect crop growth and limits its use. It was therefore hypothesized that the plant photosynthetic source could be progressively destroyed in a controlled manner using a chemical desiccant or senescing agent to simulate water deficit effects. The effects of spraying the senescing agent potassium iodide (KI), at different stages before and after anthesis, on grain yield and yield components were compared with water deficit during grainfilling using four millet hybrids grown under field conditions in 1989 and 1991.
The senescing agent KI reduced the chlorophyll content of the leaves more severely than did the water deficit treatment. Spraying with KI reduced grain yield, grain number and grain size. Effects of KI spraying at anthesis on grain yield and yield components were similar in both years and were similar to the effects of water deficits during grainfilling in 1989. Spraying with KI at the anthesis stage for each hybrid eliminated the confounding effects of phenology often encountered in water deficit treatment. We conclude that in pearl millet, spraying a senescing agent at anthesis is effective in simulating the reduction of current photosynthesis that occurs during posts anthesis water deficit and can be used as a screening method to evaluate genetic response to water deficit during grainfilling in the normal season.