Stomatal conductance and CO2 assimilation as screening tools for drought resistance in sorghum

Abstract

Stomatal conductance and CO2 assimilation were evaluated at three different levels of soil water availability as tools for estimating relative drought resistance in sorghum (Sorghum bicolor (L.) Moench) at vegetative stage (preanthesis). Four genotypes differing in drought resistance in the field (A Texas line TX 622; Oklahoma lines, BOK 11 and BOK 111; and IN-15, a line from the Sudan of Africa) were investigated. Plants were grown in a growth chamber at 27 °C, (day/night) day length of 14 h and photosynthetic photon flux density of 350 μmol m−2 S−1. Three weeks after germination, plants were divided into control, 50% and 25% soil water saturation groups. At the end of the second week of treatment, simultaneous measurements were made of stomatal conductance, CO2 assimilation, leaf water potential and transpiration, on the youngest most mature leaf. After gas exchange measurements were taken, leaf water potential was measured. In a separate experiment, survival rate under water stress conditions was also determined on plants grown under the same conditions as above. Four weeks after germination, the plants were subjected to two cycles of drought and the survival rate and growth of each genotype determined. Survival rate and growth throughout dought cycles I and II was, in the decreasing order of, IN-15, BOK 111, TX 622 and BOK 11. Water potential, stomatal conductance and CO2 assimilation of each genotype declined with decreased soil water availability; the smallest decrease was observed in IN-15 and the largest decreases in BOK 111, followed by TX 622 and BOK 11. Water use efficiency of each genotype was increased, in the same order as above, with decreased soil water availability. This correlates with the ranking obtained in the artificial drought test. In conclusion, stomatal conductance and CO2 assimilation appear to be useful tools for screening sorghum genotypes at vegetative stage (preanthesis) of growth for drought resistance. Key words: Water potential, water use efficiency (WUE), Sorghum bicolor (L.) Moench