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ARS Home » Plains Area » Fargo, North Dakota » Edward T. Schafer Agricultural Research Center » Sunflower Improvement Research » Research » Publications at this Location » Publication #416206
Research Project: Sunflower Yield, Crop Quality, and Interactions with Biotic and Abiotic Stressors

Location: Sunflower Improvement Research

Title: Precise, quantitative measurement of sunflower capitulum inclination: a trigonometry-based approach

Author
item DEVALK, EMILY - NORTH DAKOTA STATE UNIVERSITY
item Koehler, Brady
item Hulke, Brent

Submitted to: Agronomy Journal
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 9/18/2024
Publication Date: 10/12/2024
Citation: Devalk, E.M., Koehler, B.D., Hulke, B.S. 2024. Precise, quantitative measurement of sunflower capitulum inclination: a trigonometry-based approach. Agronomy Journal. 1-8. https://doi.org/10.1002/agj2.21708.
DOI: https://doi.org/10.1002/agj2.21708

Interpretive Summary: Cultivated sunflowers exhibit a unique trait called head inclination, which is simply the angle at which the seed head faces at maturity. This trait is extremely important to seed development, resistance to disease, and prevention of bird predation before harvest. Despite the importance, there is no method yet developed to precisely quantify head inclination angle in repeatable manner. Our work compared three methods to quantify head inclination angle, and estimated repeatability (or heritability), efficiency (in terms of time) and correlation of the methods. All three methods were highly correlated with each other, but one that is based on the difference in height at bloom and at maturity had the highest repeatability with high efficiency. This provides, for the first time, a means to quantify head inclination angle, which makes selection of this trait easier using modern breeding methods.

Technical Abstract: Sunflower (Helianthus annuus) is a widely cultivated crop which exhibits a trait known as capitulum (or head) inclination at maturity. This trait is influenced by various structural factors, including head weight, stem traits, and plant height. A sunflower head should be at an angle at which the head faces the ground to avoid damage from the sun and birds. While this desired inclination is known, current methods, including visual estimation and a model of measuring inclined length of the stem, fail to provide precise measurements of angle. This study introduces several novel approaches to mathematically measure the head inclination angle. The research, which was conducted over the 2022 and 2023 growing seasons, involved an aluminum rod equipped with length measurements and a digital protractor to measure various height and angle components. Using the data collected, three methods were applied for measuring inclination: a previously published model as a control, a trigonometry-based approach using angle and height measurements, and other model-based approaches. A linear model resulted in a formula to calculate the head angle of any plant based solely on two height measurements, the highest point of the plant at both bloom (R5) and maturity (R9). Calculations of heritability and correlation suggest this method has created a precise alternative to existing estimation methods. The resulting formula has the potential to be paired with measurements from high-throughput phenotyping methods, such as those facilitated with drones and ground robots, to fully automate the process of collecting head inclination data.