Identification of hybrids of spelt and wheat and their parental forms using shape and color descriptors

Grain images of three common wheat varieties, five spelt breeding lines and 24 single hybrids between wheat and spelt were subjected to principal component analysis (PCA). The values of shape descriptors (Area, Perimeter (Perim.), Feret’s Diameter (FD), Minimal Feret’s Diameter (MFD), Circularity (Circ.), Aspect Ratio (AR), Roundness (Round.), Solidity (Solid.)) and color descriptors (H S I and L a b, calculated based on average and modal values of R G B for every kernel image) were analyzed. The results indicate significant differences between the group of 24 hybrids and their parental forms. In the majority of cases, the average values of variables describing hybrid grain were within the range of values reported for wheat and spelt. The geometric features of hybrid grain, excluding Area and MFD, were marked by greater variation than wheat cultivars and spelt lines. The highest variation of color components was reported in respect of common wheat. Parental partner configuration (Triticum aestivum × Triticum spelta vs. T. spelta × T. aestivum) had no effect on color variation in hybrid grain images. Grain images characterized by higher values of H (shift from red to yellow) or L had also higher Circ. values, while grain images characterized by lower values of this shape descriptor were closer to red in hue and darker in color. PCA supported strong discrimination of the studied forms as regards their shape and color descriptors. In the PCA investigating shape descriptors only, the percentage of variation explained by the first two PCs reached a high 98.98%, whereas it was determined at 90.27% for color descriptors. The PCA of variables describing the shape and color of grain images supports reliable discrimination of hybrids and their parental forms. The applied method may facilitate the identification of hybrids between common wheat and other Triticum species, and the selection process in creative breeding.

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► Significant differences were observed between hybrids and their parental forms.
► Shape and color of hybrid grain images fall in the mid-range for their parents.
► PCA supports a very strong discrimination of all studied forms.
► PCA of grain image descriptors may be an useful technique for hybrid identification.