Diagnosis of freezing stress in wheat seedlings using hyperspectral imaging

Low-temperature freezing stress of wheat seedlings adversely influences growth and the final yield of wheat. Imaging spectrometry and image integration were used to study the extent of freezing injury on wheat seedlings on three dates in 2010. Thirty wheat cultivars with limited freezing resistance that are usually grown in Southern China were grown in pots located outdoors in Beijing. Imaging spectra of potted wheat samples were acquired in the spectral range of 450–900 nm, and a polyphenol tester was used to determine the nitrogen balance index of wheat samples. Increased freezing injury was related to increased spectral reflectance in the 450–650 nm wave band and decreased spectral reflectance in the 700–900 nm wave band. Average spectral reflectance of wheat seedling canopies was negatively correlated (−0.7) with nitrogen balance index in the red edge area between 650 nm and 700 nm. Absolute values of correlation coefficients under freezing stress at three measuring dates reached a maximum at 680 nm, and this wavelength was used as the characteristic wavelength for freezing-injury diagnosis of the wheat seedlings. From spectral images at this characteristic wavelength, it was feasible to intuitively observe the area and extent of freezing-injured wheat seedlings. Our results show that it is feasible to monitor freezing stress of wheat seedlings by use of hyperspectral imaging which could accurately reflect freezing-injured parts of wheat seedlings.