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Different parts of leaves have different tissue structures and chlorophyll contents.Therefore, fluorescence characteristics in different parts of the same leaf have lateral heterogeneity,but using fiber optic probes to obtain fluorescence characteristics of a point is difficult to reflect photosynthetic characteristics of an entire leaf.Based on plant chlorophyll fluorescence imaging techniques, the lateral heterogeneity of photosynthesis of wheat leaves infected with powdery mildew was analyzed, which was represented by variation coefficient (CV).Fluorescence imaging monitoring system can even applied to detect the invisible damages in early period, thus revealing the stress state and demonstrating the damage mechanisms.Modulated pulse fluorescence analyzer (Imaging-Pam Mini-version: 24 × 32 mm) has a relatively large detection window to acquire fluorescence parameters within a range of 24 × 32 mm.In addition, fluorescence imaging system can clearly distinguish leaf lesion area and non-lesion area due to its visual advantage.Powdery mildew lesion areas on wheat leaves are covered by conidiospores of pathogenic bacteria.Due to the differences in the thickness and status of covering layer, chlorophyll fluorescence characteristics of the lesion areas are relatively complex.Currently, few studies have been reported on the advantages of fluorescence imaging system combining with disease stress.Therefore, in this study, two selection methods of area of interest (AOI) were adopted as data sources which respectively represent the conventional optical fiber probe mode and visualization window mode,characteristics of the fluorescence differences in rapid light-response curve between non-lesion area and mixing area of wheat leaves infected with powdery mildew were investigated, to reflect the "critical state" of fluorescence characteristics of infected leaves and explore the dynamic changes in light response of wheat leaves under stress of different levels of powdery mildew, which provided theoretical basis for the in-depth research of fluorescence characteristics of wheat diseases.During March-June 2012, the experiment was carried out in National Precision Agriculture Experimental Base of Xiaotangshan Town, Changping District, Beijing City, China.Wheat heading stage (May 10, 2012) is the outbreak period of wheat powdery mildew in experimental plots.Wheat leaves infected with different incidence levels of powdery mildew (top second leaf) in various experimental plots were collected as experimental samples.This study aimed to investigate the variation characteristics of rapid light-response curves of wheat leaves infected with powdery mildew.According to the heterogeneity between two selection patterns of area of interest (AOI), determination of fluorescence induction parameters and fitting of rapid light-response curves were conducted based on fluorescence imaging system in wheat powdery mildew experimental plots.The results showed that relative electron transport rate rETR was reduced with the increase of disease severity level;rETR of the rectangle selection pattern was relatively low.Specifically, the reduction in rETR is mainly influenced by the decrease of absorption coefficient Abs.Among fitting parameters of rapid light-response curves, the maximum potential relative electron transport rate, initial slope, light suppression parameter and semi-saturation intensity were reduced with the increase of disease severity level;the heterogeneity of fitting parameters between two selection patterns reflected the "critical state" of leaf fluorescence characteristics.Infected leaves at severe level (80%) had relatively low light-harvesting capacity and tolerance to strong light, which easily caused light inhibition.According to the lateral heterogeneity analysis of photosynthesis of wheat leaves infected with powdery mildew, there was relatively high heterogeneity between fluorescence parameters of wheat infected leaves, especially in leaves with lesions on the surface.