Quantitative evaluation of the degree of sprout leaf bending of rice cultivars using P-type Fourier descriptors and principal component analysis

In quantitative studies of the shapes of plant organs, evaluation methods based on image analysis in terms of Fourier translation and principal component analysis have been recognized as important and useful methods. However, these methods cannot be used to evaluate the degree of bending of grass-type leaves. In this study, we provide a novel quantitative evaluation method that has been developed from a new type of Fourier translation named the P-type Fourier translation. It is an effective technique for evaluating the degree of bending of grass-type leaves. We have successfully applied this method to quantitatively evaluate the degree of bending of leaves of eight rice cultivars. The degree of bending of each rice leaf was evaluated in terms of several orthogonal principal component scores of P-type Fourier descriptors (F-PCs). It has been found in the present study that a few F-PCs are sufficient to quantitatively evaluate the essential variation among different rice cultivars. These inherent essential variations among rice cultivars are mainly described by only two individual F-PCs; the other variations such as the wilt caused by sunshine damage are described by another F-PC. The results also show that the F-PCs can somewhat differentiate the reasons for variation in the degree of bending. Because the F-PCs are independent from each other, they can be used as input data for QTL analysis.