Abstract:
Wheat stripe rust, caused by
Puccinia striiformis, is one of the most serious diseases on wheat yield. It is of great significance to timely and accurately detect the disease, in order to monitor and prevent the wheat stripe rust. The stripe rust can infect the internal physical and chemical characteristics and external morphological structure of wheat. Solar-induced chlorophyll fluorescence (SIF) can be expected for the remote sensing detection of crop stress. The red-band sunlight-induced chlorophyll fluorescence (RSIF) has more information about photosystem II (PSII), thus sensitively representing the photosynthetic physiological state of plants. The SIF escape rate is closely related to the canopy geometry, leaf optical properties, and light energy utilization efficiency of vegetation. In this study, field-measured data was used to invert and calculate the SIF and its escape rate (ε
CP) at different scales (canopy scale SIF
Canopy and photosystem scale SIF
PS) in the red and far-red band. The contents of four wheat pigments were obtained to combine the leaf area index (LAI) closely related to vegetation growth. The physiological basis of RSIF escape rate (Rε
CP) was determined to monitor the wheat stripe rust. Subsequently, the response characteristics of Rε
CP under stripe rust stress were explored to compare with the SIF and its derived parameters (fluorescence yield Ф
F, apparent SIF yield SIF
y) in the red and far-red light bands, the normalized difference vegetation index (NDVI), the MERIS terrestrial chlorophyll index (MTCI) and the simple ratio vegetation index (SR). We also systematically analyzed the response characteristics of Rε
CP to disease severity level (
DSL) under different
DSL and chlorophyll (Chl) levels. The results revealed that the correlations between nitrogen balance index (NBI), Chl, flavonoids (Flav), anthocyanins (Anth), LAI, and
DSL were all extremely significant, with the highest correlation observed between Chl and
DSL. Rε
CP showed extremely significant correlations with NBI, Chl, Flav, and Anth, outperforming RSIF and far-red Sun-induced chlorophyll fluorescence (FRSIF) at the photosystem scale and being superior to FRSIF at the canopy scale in relation to LAI. This indicates that Rε
CP better reflects crop physiological and canopy structural changes induced by disease stress. Among various characteristic variables such as canopy-scale FRSIF (FRSIF
Canopy), photosystem-scale FRSIF (FRSIF
PS), RSIF (RSIF
PS), apparent SIF yield in the red band (RSIF
y), its fluorescence yield (RФ
F), NDVI, MTCI, and SR, Rε
CP exhibited the highest correlation with
DSL. For both mild to moderate (0<
DSL≤45%) and severe (
DSL>45%) disease conditions, the correlation between Rε
CP and
DSL was higher than that of SIF, its derived parameters, and vegetation indices, all reaching extremely significant levels. Rε
CP was more sensitive to changes in
DSL, surpassing other parameters. Whether under low (Chl≤30) or medium-to-high (Chl>30) Chl content, Rε
CP demonstrated the most sensitive response to wheat stripe rust stress, with its correlation with
DSL superior to the extremely significant levels achieved by SIF and its derived parameters, as well as vegetation indices. Therefore, Rε
CP can serve as a suitable factor for remote sensing monitoring of wheat stripe rust, which is of great significance for disease prevention and yield enhancement. This study also provides a robust reference and tool for remote sensing monitoring of crops in agricultural production, incorporating RSIF and escape ratio into remote sensing monitoring to significantly enhance the detection and monitoring of plant health status.