Study on Photosynthetic Rate of Wheat under Powdery Mildew Stress using Hyperspectral Image

摘要

In order to monitor wheat powdery mildew in real time and identify crop diseases in a large range by remote sensing, the relationships of spectral reflectivity and net photosynthetic rate (Pn) with disease index of wheat were clarified under the stress of powdery mildew, and the variation of photosynthetic rate was predicted using spectral vegetation index. The experiment was conducted during the winter wheat growth season of 2016?2017, and the wheat variety Jimai 15 (control) susceptible to powdery mildew, and Jimai 22 and Luyuan 502 resistant to powdery mildew, were used as the test materials. Based on the inoculation test of powdery mildew by plot test in field, the photosynthetic rate, spectral reflectivity and disease index of wheat flag leaves were measured and investigated every 7~12 days from heading stage to milk-ripe stage. It was found that the Pn of normal leaves of Jimai 22 and Luyuan 502 was larger than that of diseased leaves at flowering stage, and the spectral reflectivity of the leaf spots was higher than that of normal leaves at filling stage. The photosynthetic rate and spectral reflectivity of the control and Jimai 22 were positively correlated, while those of Luyuan 502 were significantly negatively correlated. In the visible light range, the spectral reflectivity increased with the increase of disease index. At the reflectivity platform, the spectral reflectivity decreased with the increase of disease index. The inversion models of photosynthetic rate were established based on the ratio vegetation index of the three cultivars, and their R2 values were 0.551~0.994 and reached significant or extremely significant level. Therefore, using the ratio vegetation index to invert the photosynthetic rate could obtain better effect during the growth period of wheat.