Stomatal density and aperture dynamics regulate drought response and yield in tomato.

In crops, key physiological traits such as transpiration, stomatal conductance, and photosynthesis are closely linked to productivity. However, these dynamic traits are often studied under steady-state conditions or modeled with limited data, failing to capture the plant's versatile responses to dynamic field conditions. We hypothesized that natural variation in stomatal morphological traits, specifically, abaxial-to-adaxial distribution and density regulate the temporal physiological response patterns in tomato introgression lines (ILs; crosses between WT, S. Pennellii, and M82 lines). We further hypothesized that differences in these response patterns could explain key variations in drought response and yield. To test this, we performed continuous and simultaneous functional phenotyping on IL populations with a well-documented multi-year field yield history. Our results revealed high plasticity in the dynamic water balance regulation of ideotypic ILs (plants with good yield performance under various field conditions). The ideotype lines exhibited higher transpiration and growth rates under well-irrigated conditions than the other lines. Moreover, the ideotype lines exhibited rapid stomatal canopy conductance responses to changing conditions and quick recovery after drought. Anatomically, these lines had high abaxial-to-adaxial stomatal density ratios and stomatal apertures that peaked early in the day, even under water-deficit conditions. Our study demonstrates how a functional phenotyping approach of the whole-plant water-loss measurements can help us understand and identify dynamic, complex, yield-related physiological traits.