Optical Flow-Based Analysis of the Relationships between Leaf Wilting and Stem Diameter Variations in Tomato Plants

Abstract

<jats:p>The estimation of water stress is critical for the reliable production of high-quality fruits cultivated using the tacit knowledge of expert farmers. Multimodal deep neural network has achieved success in the estimation of stem diameter variations as a water stress index, calculated from leaf wilting and environmental data. However, these studies have not addressed the specific role of leaf wilting in the estimation. Revealing the role of leaf wilting not only ensures the reliability of the estimation model but also provides an opportunity for improving the estimation method. In this paper, we investigated the relationships between leaf wilting and stem diameter variations without resorting to black-box approaches such as deep neural network. To clarify the role of leaf wilting, this study uses cross-correlation analysis to analyze the time lag correlation between leaf wilting, quantified by optical flow, and stem diameter variations as a water stress index. The analysis showed that leaf wilting had a significant time lag correlation with short-term stem diameter variations, which were water stress responses in plants. As the results were consistent with known plant water transport mechanisms, it was suggested that leaf wilting quantified by optical flow can explain short-term stem diameter variations.</jats:p>

Dendrometer Stem Monitoring of Tomato Plants Attacked by Whiteflies in Greenhouses

“…The dendrometer connected to a data logger must always be in contact with the plant surface and avoid direct solar radiation [24]. LVDT sensors are used by most researchers where thin stems are sampled [25], but tomato plant stem was measured with precision with laser displacement sensors [26]. In our comparison between linear resistance and LVDT sensors the final error after 4 months of measurement was of only 0.01mm.…”

“…However, a severe infested plant is completely stressed, leaves fall and stem diameter decreases. Leaf wilting and stem diameter response have been related to plant water stress [26]. Water stress affects soil water potential and stomatal conductance [28,29].…”

High-throughput field crop phenotyping: current status and challenges

“…Structural changes in plants, such as leaf wilting, which is detectable by image analysis, can also be an indicator of water stress ( Srivastava et al 2017 , Wakamori and Mineno 2019 ). Another way to estimate water stress is to use models or indices based on hyperspectral or multispectral images ( Asaari et al 2019 , Romero et al 2017 , 2018 , Thorp et al 2018 ).…”

Image-Based Plant Wilting Estimation

“…These methods require acquiring individual leaves so they are very labor intensive. Other methods such as [22,31] also use RGB images for estimating wilting, but they require special equipment such as guided rail cameras and laser sensors [31] or field servers [22]. Our method uses RGB images from multiple views using a single RGB camera which requires much less equipment and labor.…”