A simple, fast and accurate screening method to estimate maize (Zea mays L.) tolerance to drought at early stages

There is a great need for the selection of plants with higher drought tolerance, so that fast and effective techniques to identify variations in drought tolerance are mandatory for screening large numbers of genotypes. This work presents a protocol for easy and reliable assessment of responses of maize genotypes to water stress conditions imposed during early stages of development. Three experiments using 11 commercial maize hybrids under four levels of water stress were carried out: (1) germination, (2) seedling growth, and (3) early growth bioassays. Constant and uniform water stress was imposed using solutions of polyethylene glycol 6000 (PEG 6000). Plant material was evaluated for several morphological, physiological and biochemical traits and monitored for photosynthetic efficiency. Principal component analysis (PCA) of these joint experiments revealed that germination percentage, early root development and stomatal conductance were the most useful traits for discriminating maize hybrids according to their tolerance to water stress. A subsequent greenhouse assay performed with two hybrids with contrasting responses under soil drying conditions validated the previous results. According to our results, the key of drought tolerance was a rapid response of stomatal conductance, which allowed a longer survival to stress even under severe desiccation. This work provides the researcher with a simple and reliable screening method that could be implemented as a decision support tool in the selection of the most suitable genotypes for cultivation in areas where water availability is a problem, as well as for the selection of tolerant genotypes to early drought in breeding programs