Assessment of a non-destructive method to estimate the leaf area of Armoracia rusticana

The aim of the study was to analyse horseradish growth for developing a mathematical model to estimate the leaf area based on linear measurements of the leaf surface. Leaf area (LA), number and morphometric characteristics of the leaves including lamina length (L) and width (W) were evaluated on two horseradish accessions (Cor and Mon) throughout a two- years growing cycle. In both accessions, increased values of LA and leaf number were found by comparing the second with the first growing season. Leaf development occurs along with variations in size and not in shape during the plant growth. The leaves are elliptical in shape but tend to be wider and bigger in Cor accession and tapered and similar to narrow ellipses in Mon showing different length/width relationship. Consequently, several regression models relating the LA and L, W, L2, W2 individually or in combination were fitted for each accession based on a set of 1000 leaves. The horseradish LA can be predicted based on either length or width alone. However, the regression linear model LA = aLW + b (LA = 0.71LW - 0.27 and LA = 0.76LW - 3.22 for Cor and Mon, respectively) provided the best LA estimation (R2 > 0.95). The validation of this latter model showed high correlation between LA measured and LA predicted in both accessions (R2=0.98). Considering the type of foliage of horseradish, the proposed model can be used to estimate the leaf area throughout the entire crop cycle