In-field methods for rapid detection of frost damage in Australian dryland wheat during the reproductive and grain-filling phase

Abstract

Abstract. Frost damage causes significant production losses and costs to Australian dryland wheat, and frost impacts are not expected to decline in the near future, despite global warming. Rapid estimation of frost damage to crops on a spatial basis would allow for timely management decisions to reduce the economic impact of frost events. In this paper, we take a first step in evaluating the utility of hyperspectral reflectance and active light fluorescence for detecting frost damage to wheat during its reproductive phase. Two experiments were conducted immediately after the first observation of frost damage, (i) in 2006, five plots in an existing trial were opportunistically subdivided to take spectral reflectance measurements on frost damaged plants along with yield measurements, and (ii) in 2015, a transect across 31 rows within a commercial paddock was established to evaluate spectral reflectance, fluorometer measurements, and yield along a gradient from non-frosted to frost damaged plants. The results of the hyperspectral reflectance data appeared variable in response across the two experimental sites where frost was observed in-crop. In 2006, hyperspectral-derived indices showed significant differences (P < 0.05) between measurements of frosted and non-frosted canopies, but this was not the case for observations taken in 2015, where the mean response was reversed between experimental sites for several of the indices. In contrast, fluorometer measurements in the 2015 trial resulted in higher correlations with yield and observed frost damage compared with the reflectance measurements. Seven of the nine fluorometer indices evaluated were correlated with yield (used as an indicator of frost damage) at P < 0.01. An index of compounds which absorbs at 375 nm, FLAV, had the best correlation coefficients of 0.91 and 0.90 for the two dates in 2015. The fluorescence index FLAV was selected to evaluate whether it could be used to classify the canopy as frost affected or not, using discriminant analysis for the 2015 transect data. The overall classification accuracy, defined as the number of correctly classified measurements (57) divided by the total number (62) was 92%. The present study was not able to provide insight into how rapidly the sensors could detect frost damage before detection with the naked eye, as the survey data constituted a transect based on early visual symptoms, however this study does provide important insight into what sensors and/or indices may be sensitive to 'seeing' early frost damage in-crop. The next steps, which build on this work and need to be resolved are (i) what is the nominal scale of measurements required, and for which portions of the plant canopy? (ii) How robust (over space and time) are any relationships between frost damage and index response? (iii) Can frost damage be detected before the onset of visual damage?

Frost response in wheat and early detection using proximal sensors

“…Correlation coefficients between fluorometer indices and cold loads for flag leaf and head field of view. also correlated with wheat yield linked with frost damage (correlations of 0.76 at anthesis (Zadoks 65), and 0.80 at Zadoks 71) in an earlier study (Perry et al, 2017). In this previous work, the FLAV index, which is proportional to the flavanol content of leaf and fruit and essential for pigments, had the best correlation with yield (as an indicator of frost damage).…”

“…The fluorescence‐derived indices, FRF_G and SFR_G, were consistently well correlated with cold load applied to wheat, across both plant component (leaves and heads) and time intervals from frost application. The SFR_G index, which is related to chlorophyll content, also correlated with wheat yield linked with frost damage (correlations of 0.76 at anthesis (Zadoks 65), and 0.80 at Zadoks 71) in an earlier study (Perry et al., ). In this previous work, the FLAV index, which is proportional to the flavanol content of leaf and fruit and essential for pigments, had the best correlation with yield (as an indicator of frost damage).…”

“…Comparison of an earlier study (Perry et al., ) on indices sensitivity to wheat yield affected by natural frost showed that the reflectance index CCCI was significantly different for frosted versus non‐frosted canopies; where CCCI was designed to account for biomass when estimating canopy chlorophyll, combining both NDVI and NDRE (Fitzgerald, Rodriguez, & O'Leary, ; Perry et al., ). Similarly, PRI showed consistently higher values for the frosted canopy, consistent with the positive correlation to cold loads seen in the current analysis.…”

“…Fluorescence measurements have been used for wheat to characterize leaf nitrogen (Fernandez-Jaramillo et al, 2012;Bürling, Hunsche, & Noga, 2011) and water stress (Bürling et al, 2013), and have been shown to relate to freezing tolerance assessments in leaves from wheat (Rapacz & Woźniczka, 2009) and triticale (Rapacz, Sasal, & Gut, 2011). More recently, the fluorescence-derived index FLAV was linked with frost damage in field-grown wheat (Perry, Nuttall, Wallace, & Fitzgerald, 2017).…”

Sustainable and technological strategies for basic cereal crops in the face of climate change: A literature review

“…Frederiks et al (2015) evaluated damage caused by radiant frost, identifying it after the emergency phase; Crimp (2016) studied frost using the Stevenson screen at 2°C at ground level and temperature threshold; similar work is done by Perry et al (2017), who used evaluation sensors before achieving it with the naked eye. As mentioned earlier, the results consisted of identifying the most sensitive and the most resistant stages.…”