USE OF THE SENESCING AGENT POTASSIUM-IODIDE TO SIMULATE WATER-DEFICITDURING FLOWERING AND GRAINFILLING IN PEARL-MILLET

Grain growth in cereal crops is largely dependent on the availability of current photosynthates. Water deficits during flowering and grainfi lling 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-f ree season by withholding irrigation during the desired treatment peri ods. The former approach is time consuming due to the erratic nature o f drought patterns. In the latter approach, temperatures and daylength during the dry periods often affect crop growth and limits its use. I t was therefore hypothesized that the plant photosynthetic source coul d be progressively destroyed in a controlled manner using a chemical d esiccant or senescing agent to simulate water deficit effects. The eff ects of spraying the senescing agent potassium iodide (KI), at differe nt stages before and after anthesis, on grain yield and yield componen ts were compared with water deficit during grainfilling using four mil let hybrids grown under field conditions in 1989 and 1991. The senesci ng agent KI reduced the chlorophyll content of the leaves more severel y than did the water deficit treatment. Spraying with KI reduced grain yield, grain number and grain size. Effects of KI spraying at anthesi s on grain yield and yield components were similar in both years and w ere similar to the effects of water deficits during grainfilling in 19 89. Spraying with KI at the anthesis stage for each hybrid eliminated the confounding effects of phenology often encountered in water defici t treatment. We conclude that in pearl millet, spraying a senescing ag ent at anthesis is effective in simulating the reduction of current ph otosynthesis that occurs during posts anthesis water deficit and can b e used as a screening method to evaluate genetic response to water def icit during grainfilling in the normal season.