# Application of Hyperspectral Imaging for Assessment of Tomato Leaf Water Status in Plant Factories
## 3 Results and Discussion  
### Tomato Leaf Water Status  
In the agricultural production of tomato, the increase of plant stress, especially water stress, is widely used to improve the tomato fruit quality. However, it is difficult to accurately control the amount of plant stress given. The desired effect cannot be achieved with insufficient plant stress; on the other hand, excessive increase of plant stress will cause damage to the plant, even if the amount of plant stress is slightly larger than optimal. Tomato leaf water status has been adopted as an index to evaluate plant stress because leaves are the most susceptible organs to water stress compared with other organs, such as the fruit, as noted earlier. Although the leaf water potential can be a strong indicator for assessing the tomato leaf water status, WC was employed as an indicator in this experiment because it is easy to measure and is a stable parameter [25].  
The tomato leaf from Leaf Position 1 (LP-1) (Table 1) has a significantly lower FW than those from Leaf Position 2 (LP-2) and Leaf Position 3 (LP-3). This is considered to be owing to the LP-1 tomato leaf being a new leaf and being located much closer to the growth point. There are significantly different WCs among the LP-1, LP-2, and LP-3 tomato leaves, the averages of which are 86.88%, 89.12%, and 90.25%, respectively. The higher the leaf position is, the smaller the leaf area (LA). The fresh weight per unit leaf area (FW/LA) and equivalent water thickness (MC) in LP-1 are significantly smaller than those in LP-2 and LP-3.  
For the different tomato cultivars (Figure 5), \"DR03-103\" shows a higher leaf FW and leaf area than the other tomato cultivars. Differences in WC are observed among the different cultivars. The highest leaf WC is observed in the typical Japanese cultivar \"CF Momotarou\", with a 3.77% difference between LP-3 (87.58%) and LP-1 (91.35%). The lowest leaf WC is observed in the Dutch \"Endeavour\" tomato cultivar, with a difference of 2.80% between LP-3 (86.12%) and LP-1 (88.92%). The equivalent water thickness (MC) shows almost the same value in LP-2 and LP-3, whereas the WC in the LP-3 leaf is on average 1.13% higher than the WC in the LP-2 leaf. This difference is considered to be due to the influence of the water potential, which may depend on the height difference of the leaf position.  
\begin{table}
\begin{tabular}{l c c c c c} \hline  & **FW (g)** & **WC (\%)** & **LA (cm2)** & **FW/LA (g/dm2)** & **MC (g/dm2)** \\ \hline LP-1 & 1.19 b & 86.88 c & 48.96 b & 2.30 b & 2.00 b \\ LP-2 & 1.89 a & 89.12 b & 67.31 a & 2.75 a & 2.48 a \\ LP-3 & 2.02 a & 90.25 a & 73.11 a & 2.79 a & 2.49 a \\ \hline \end{tabular} FW: fresh weight, WC: water content, LA: leaf area, FW/LA: fresh weight per unit leaf area; MC: equivalent water thickness. Values with different letters are significantly different according to [PERSON]’s test at \(p<0.05\).  
\end{table}
Table 1: Characteristic differences of the tomato leaves according to height layers.  
Figure 5: Tomato leaf characteristics of five cultivars under different height layers. (**a**) Fresh weight; (**b**) water content; (**c**) leaf area; (**d**) equivalent water thickness (g/dm2). E: Endeavour; R: Rinnka409; T: Tomimaru mucyo; Y: [PERSON]; Z: DR03-103.