Spectrum Characteristics of Cotton Single Leaf Infected by Verticillium Wilt and Estimation on Severity Level of Disease

【Objective】The aims are elucidation of spectrum characteristics of cotton leaf infected by verticillium wilt and estimation of its SL ( severity level ) and providing theoretic foundation for further monitoring cotton verticillium wilt at large scale using airborne and airspace remote sensing. 【Method】The spectrum reflectance of cotton single leaf infected by verticillium wilt was measured in cotton disease nursery and field in different growth phases, in the meanwhile, SL of single leaf infected by verticillium wilt was investigated. The method of first derivative spectrum was used to estimate accurately the disease of cotton single leaves infected by compared with the reflectance spectrum of different single leaves infected by verticillium wilt. 【Result】 The results indicated that spectrum characteristics of cotton leaf infected by verticillium wilt had better regularity with the increase of SL in different periods and varieties. Spectrum reflectance increased significantly in visible light region (400-700 nm) and near-infrared region (700-1 300 nm) with the increase of the SL, and especially significant in visible light regions (525-680 nm). When SL attained b2 (25%), cotton leaf infected by verticillium wilt could be used as a threshold and diagnose index in early period. There were evident different characteristics of first derivative spectra in these diseased leaves, it changed significantly in red edge ranges (680-780 nm) in different SL, red edge of first derivative spectrum swing decreased, and red edge position equal moved to the blue. The results indicated that 434-724 nm and 909-1 600 nm should be selected out as sensitive bands region to SLof single leaf. Some inversion models for estimating cotton leaf SL of verticillium wilt all reached the best significant level. 【Conclusion】The results suggested that different spectrum characteristics of cotton leaf infected by verticillium wilt were marked. The model in which the first derivative spectra at 723 nm could invert accurately the cotton leaf SL, and it may be used to forecast the position of cotton leaf infected by verticillium wilt quantitatively.