The Genetic and Environmental Impacts of Alfalfa Forages on the Optical Parameter in Terahertz Range

The 13 species of alfalfa forages from four different regions with similar climate environment were studied via terahertz time-domain spectroscopy (THz-TDS). The refractive index in the frequency interval of 0.2–1.2 THz was calculated as a characteristic parameter based on the frequency spectrum, where the maximal difference reaches approximately 0.2. To illustrate the interspecific relationship, principal component analysis (PCA) was implemented using the refractive index. According to the first two principal components, genetic factors—regardless of origins—mainly contribute to the distance of the dataset. In hybridization, the PC score of the cross is determined by its parents, while exchanging male and female parents has impact on the conclusion. If the parents of cross A and cross B are in the same family, then their PC scores are close. Plants with similar genes that were cultivated in similar environments (including sunshine time, precipitation, and temperature) tend to have identical PC scores.