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Detection of Bread Wheat Senescence Rate using UAV Imagery

UAV-measured spectral vegetation indices showed a promising result of estimating the senescence rate of bread wheat in the field.
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a) Location of the field trial, b) unmanned aerial vehicle (UAV) platform, and c) orthomosaic images generated at mid grain filling stage (Figure 1)

Measurement of crop phenological stages is important for plant breeding yet requires significant efforts and skills. Awais Rasheed and Zhonghu He from CIMMYT participated in a research project using UAVs to address this issue, piloting to detect the senescence rate of bread wheat in the field. The study, recently published in Remote Sensing, showed the promising result of using the spectral vegetative indices derived from UAV-measured imagery to estimate the senescence rate under two different water management regimes.

Abstract
Detection of senescence’s dynamics in crop breeding is time-consuming and needs considerable details regarding its rate of progression and intensity. Normalized difference red-edge index (NDREI) along with four other spectral vegetative indices (SVIs) derived from the unmanned aerial vehicle (UAV) based spatial imagery, were evaluated for rapid and accurate prediction of senescence. For this, 32 selected winter wheat genotypes were planted under full and limited irrigation treatments. Significant variations for all five SVIs: green-normalized difference vegetation index (GNDVI), simple ratio (SR), green chlorophyll index (GCI), red-edge chlorophyll index (RECI), and normalized difference red-edge index (NDREI) among genotypes and between treatments, were observed from heading to late grain filling stages. The SVIs showed the strong relationship (R2 = 0.69 to 0.78) with handheld measurements of chlorophyll and leaf area index (LAI), while negatively correlated (R2 = 0.75 to 0.77) with canopy temperature (CT) across the treatments. NDREI as a new SVI showed higher correlations with ground data under both treatments, similarly as exhibited by the other four SVIs. There were medium to strong correlations (r = 0.23–0.63) among SVIs, thousand grain weight (TGW) and grain yield (GY) under both treatments. Senescence rate was calculated by decreasing values of SVIs from their peak values at the heading stage, while variance for senescence rate among genotypes and between treatments could be explained by SVIs variations. Under limited irrigation, 10% to 15% higher senescence rate was detected as compared with full irrigation. Principle component analysis corroborated the negative association of high senescence rate with TGW and GY. Some genotypes, such as Beijing 0045, Nongda 5181, and Zhongmai 175, were selected with low senescence rate, stable TGW, and GY in both full and limited irrigation treatments, nearly in accordance with the actual performance of these cultivars in the field. Thus, SVIs derived from UAV appeared as a promising tool for rapid and precise estimation of senescence rate at maturation stages.

Hassan, Muhammad Adeel, Mengjiao Yang, Awais Rasheed, Xiuliang Jin, Xianchun Xia, Yonggui Xiao, and Zhonghu He. “Time-Series Multispectral Indices from Unmanned Aerial Vehicle Imagery Reveal Senescence Rate in Bread Wheat.” Remote Sensing 10, no. 6 (2018): 809. https://doi.org/10.3390/rs10060809