Toward efficient screening systems for sunflower drought tolerance: a comparative and molecular perspective

The observed longer and more frequent periods of drought in recent years have drawn more focus on efficient breeding techniques for drought-tolerant crops. Several systems have been used to simulate drought conditions in order to select drought-tolerant lines. However, little is known about the comparability of different screening methods. We compared four different systems in terms of the information provided on drought tolerance, namely, two in vitro systems (liquid and solid medium applying polyethylene glycol as the drought simulant), and two soil-based pot trials were conducted either in a green house or in a climate chamber. Two sunflower inbred lines differing in drought tolerance (AB-OR-8 and DF-AB-2) were characterized at the seedling stage using physiological and morphological parameters of shoots and roots. Transcriptomic analysis (RNA-seq) and quantitative RT-PCR were performed to compare drought responses and stress levels applied by the different systems. In an assessment of all four screening methods, the expressions of five of six selected genes in the ABA signaling pathway were differentially upregulated during drought, while one of them was downregulated. These genes represent valuable indicators of the stress level applied by a drought-screening method. The advantages and disadvantages of different drought-simulating systems were evaluated and combined with next-generation sequencing data to identify the most efficient selection approach for assessing drought tolerance in sunflower. Overall, all systems enabled effective pre-screening of the breeding material for drought tolerance, where the decision for a system depends on experimental goals and resource availability. If the goal is to maximize the molecular resolution of drought stress, the in vitro liquid system is the most effective.