Quantitative evaluation of common buckwheat (Fagopyrum esculentum Moench) kernel shape by elliptic Fourier descriptor

Kernel shape of 27 common buckwheat cultivars was evaluated quantitatively by image analysis using elliptic Fourier descriptors and their principal components. The relationships between the quantitative information on kernel shape and several agronomic characteristics were clarified. The closed contour of each kernel projection was extracted, and 80 elliptic Fourier coefficients were calculated for each contour. The Fourier coefficients were standardized so that they were invariant of the size, rotation, shift and chain-code starting point. Then, the principal components on the standardized Fourier coefficients were evaluated. The cumulative contribution at the fifth principal component was higher than 93%. It was found that the first, second, third and fifth principal components represented the aspect ratio of the kernel, the location of the kernel centroid, the sharpness of the two kernel tips and the roundness of the base in the kernel contour, respectively. Analysis of the variance indicated that genotypic differences in these principal components were significantly large. Because these variations of the principal components were continuous, the effect of polygenes on shape was suggested. The relationships between these principal components and agronomic traits, including flowering period, yield, 1000 seed weight and volume weight, were also investigated. It was clarified that the first principal component was closely correlated with agronomic traits such as flowerig period, 1000 seed weight and volume weight. In conclusion, it was clarified that principal component scores based on elliptic Fourier descriptors yield useful quantitative parameters for evaluating kernel shape for common buckwheat breeding.