Detection of Senescence Under Heat Stress Based on Leaf Reflectance Spectra for Wheat.

Premature senescence from heat stress is an important factor resulting in low yield and poor quality in wheat production. It is critical to timely detect the occurrence of premature senescence for enhancing the production especially in heat stress. Previous st manyudies showed that biophysical/biochemical parameters, such as chlorophyll content, photosynthesis and enzymatic activity, can be used to identify the senescence as indicators, but it is difficult in application due to the complex measurement procedures. Spectroscopy methods provide a convenient and efficient way to detect the dynamics change of these indicators, yet few of them were used to detect senescence. The main reason is that it is still unclear which biophysical/biochemical parameters and vegetation indices are effective for recognizing the premature senescence. In this study, leaf reflectance spectra were measured from potted wheat plants at four levels of heat stress during heading stage and filling stage. Biophysical/biochemical parameters, normalized difference spectral index (NDSI) and ratio spectral index (RSI) were used to select the most suitable spectral indices and algorithm for the detection. Results suggested that, visible region changed significantly during wheat senescence. Among those parameters, leaf chlorophyll content and photosynthesis were the sensitive indicators to characterize the process of wheat senescence with leaf chlorophyll content as better indicators than photosynthesis. NDSI (R750, R721), which had the highest R² in the estimation of leaf chlorophyll content, can detect wheat senescence as a nondestructive method effectively.