In C3 plants, carbon isotope discrimination (Δ) shows large environmental and genetic variations and is linearly positively related to Ci/Ca, the internal to atmospheric CO2 ratio. It has been proven to be an accurate predictor of yield under drought conditions. In C4 crops, information concerning Δ variation in different organs of the plant and its possible association with biomass or grain yield is still scarce. In the present study, Δ was first analyzed at flowering, under drought and well-watered conditions, in different organs of maize (Zea mays L.) inbred lines differing for drought tolerance. Leaf Δ was higher than ear and silk Δ. Drought stress significantly increased Δ in all organs. Under drought, tolerant inbred lines showed significantly higher Δ than susceptible ones. There was a significant positive correlation between leaf, ear and silk Δ, and ear dry weight at flowering, a trait closely associated to grain yield. Carbon isotope discrimination was then analyzed at flowering in leaves of a set of drought tolerant maize hybrids and checks. Drought tolerant hybrids had significantly higher grain yield and Δ than the used checks. No correlation was found, however, between Δ and grain yield within tolerant hybrids. The use of Δ appears consequently accurate for a first screening of lines or hybrids highly contrasting for drought tolerance, but not for a more advanced selection among tolerant hybrids. More studies are needed in maize and other C4 crops to establish the causes of Δ variation and precise which organ sampled and time of sampling may allow the better precision in the screening process.
Monneveux, P.; Sheshshayee, M.S.; Akhter, J.; Ribaut, J-M. Using carbon isotope discrimination to select maize (Zea mays L.) inbred lines and hybrids for drought tolerance. Plant Science (2007) 173 (4) 390-396. [DOI: 10.1016/j.plantsci.2007.06.003]