PHYSIOLOGICAL STUDIES OF PEARL MILLET AND GRAIN SORGHUM SUBJECTED TO HIGH TEMPERATURE AND MOISTURE STRESS.

摘要

Pearl millet currently persists in extremely hot and dry crop producing regions of the world. Its expansion of usage to new areas with limited water and its response to stress conditions are of interest. Thus investigations were made as to the physiological and metabolic activity of newly developed dwarfed, hybridized pearl millets under field and growth chamber conditions. Plant responses to moisture stress and temperature stress were evaluated in regard to grain filling duration and yield components.; To evaluate termination of the grain filling period, radioactive assimilate translocation to maturing kernels was used to quantify physiological maturity in relation to the kernel dark layer. The use of this visual indicator was found to be rapid and effective in judging the cessation of dry weight accumulation.; A range of field soil moisture conditions were created by a line source sprinkler system under which three genotypes each of pearl millet and of grain sorghum were observed for moisture response reactions. Plant status and crop water use were monitored on a weekly basis during each season and water use of pearl millets appeared to be equal to that of sorghums, despite lower productivity by millets. Grain yield responses of both crops increased linearly with increased evapotranspiration but millet showed a slight decrease in water use efficiency with increased supplemental water whereas sorghum displayed an increase. Pressure chamber estimates of leaf xylem pressure potential indicated that only very small differences in readings related to large differences in grain yield. Panicle gas exchange rates of both crops were not significantly different with varying soil moisture levels but were very responsive to temperature. Respiration rates of millet panicles were 50 to 100% faster than rates of sorghum panicles and may be related to the 15 to 20% shorter grain filling period noted for millets.; Several day/night growth temperature situations were evaluated for their effects on pearl millet physiological activity during GS(,2) (panicle initiation until bloom stage). Adaxial stomata were noted as much more responsive to stimulus than were the abaxial stomata. Photosynthetic rates were most rapid during GS(,2) and rates as high as 29.2 mg CO(,2)/dm('2)/hr were measured at 35 C and 800 (mu)E of PAR. Gas exchange rate monitoring subsequent to varying thermal history indicated no carry-over effects on carbon exchange rates, however, plant morphology and development was altered. Changes in both daytime and nighttime GS(,2) temperatures influenced grain yield and yield components. Favorable growing temperatures for pearl millet were near 35/25 C and were higher than the apparent temperature optimum for sorghum growth.; Leaf respiratory activity dropped considerably during the night whereas the panicle continued rapid respiration. Air within the intra-panicle void accumulated respiratory CO(,2) up to 1300 ppm.; Transpiration rates in actively growing trichomed and trichomeless pearl millet isolines did not differ in water use. Sorghum evaluated under the same set of moisture levels and temperature treatments showed higher transpiration rates with less negative plant water potentials at high temperature. This apparently related to stomata remaining more open at higher temperatures than for millet.