A necessary step towards future application of proxy traits: Field validation
The present study was conducted in controlled environments. As its objective was to identify easily measurable proxy traits for genotypic response to e-CO2 to be used for phenotyping a large number of genotypes in the context of crop improvement, a field validation will be necessary to validate their predictive potential when measured both in current and elevated-CO2 environments. Ideally, this should be done in an existing FACE experimental setup, using a population that represents both genetic/phenotypic diversity and a large number of high-yielding materials. Hasegawa (2013) demonstrated in a FACE trial in Japan that diverse levels of CO2acclimation occur among modern, high-yielding cultivars.
For future applications in crop breeding, direct selection for the proxy traits is possible if measurement costs and complexity are limited. It is also conceivable that once suitable proxy traits are found and field validated, they can be applied to larger genetic panels for association studies to identify molecular markers for them. Such markers, if performing well, might be more readily adopted by breeders than physiological measurements.