"Rolled-upness": phenotyping leaf rolling in cereals using computer vision and functional data analysis approaches.

Area of Science:

• Plant physiology
• Agronomy
• Genetics

Background:

• Wheat flag leaves roll cylindrically under drought stress, an adaptive mechanism to conserve water.
• This leaf rolling trait is crucial for maintaining leaf area duration and improving grain yield, especially in arid conditions.
• Traditional methods for quantifying leaf rolling are often confounded by differences in water uptake and transpiration, hindering objective comparisons.

Purpose of the Study:

• To develop and validate a novel, objective method for quantifying leaf rolling propensity in wheat (Triticum aestivum L.).
• To minimize confounding factors in assessing leaf rolling, enabling precise comparisons between wheat varieties and treatments.
• To provide a tool for genetically dissecting the hydronastic leaf rolling trait in cereals.

Main Methods:

• Leaf strips were immersed in an osmoticum to induce controlled leaf rolling.
• Micro-photographs of leaf cross-sections were analyzed using two quantitative approaches: convex hull properties and cubic smoothing splines.
• Cubic smoothing splines were used to mathematically approximate leaf shape and derive a statistic for comparison.

Main Results:

• The developed method provides objective measurements of leaf curvature, termed "rolled-upness."
• Both convex hull and spline-based approaches successfully differentiated between wheat lines with contrasting leaf rolling tendencies.
• The spline approach distinguished between upward and downward curvature and identified the location of maximum curvature.

Conclusions:

• Smoothing splines applied to wheat leaf cross-sections offer an objective method for measuring inter-genotypic variation in hydronastic leaf rolling.
• Mean curvature of the leaf cross-section was identified as a straightforward and effective measure for genotype discrimination.
• This method has broad applicability for studying and genetically dissecting leaf rolling in cereals.