Abstract
The ability of a genotype to stay green affects the primary target traits grain yield (GY) and grain protein concentration (GPC) in wheat. High throughput methods to assess senescence dynamics in large field trials will allow for (i) indirect selection in early breeding generations, when yield cannot yet be accurately determined and (ii) mapping of the genomic regions controlling the trait. The aim of this study was to develop a robust method to assess senescence based on hyperspectral canopy reflectance. Measurements were taken in three years throughout the grain filling phase on >300 winter wheat varieties in the spectral range from 350 to 2500 nm using a spectroradiometer. We compared the potential of spectral indices (SI) and full-spectrum models to infer visually observed senescence dynamics from repeated reflectance measurements. Parameters describing the dynamics of senescence were used to predict GY and GPC and a feature selection algorithm was used to identify the most predictive features. The three-band plant senescence reflectance index (PSRI) approximated the visually observed senescence dynamics best, whereas full-spectrum models suffered from a strong year-specificity. Feature selection identified visual scorings as most predictive for GY, but also PSRI ranked among the most predictive features while adding additional spectral features had little effect. Visually scored delayed senescence was positively correlated with GY ranging from r = 0.173 in 2018 to r = 0.365 in 2016. It appears that visual scoring remains the gold standard to quantify leaf senescence in moderately large trials. However, using appropriate phenotyping platforms, the proposed index-based parameterization of the canopy reflectance dynamics offers the critical advantage of upscaling to very large breeding trials.
Highlights
Maximizing carbon assimilation by a prolonged green leaf area duration after anthesis is a major breeding aim in many crops
The objective of the present study was two-fold: First, we aimed to develop a highthroughput method based on spectral reflectance to track visually observed senescence dynamics in a large population of morphologically diverse wheat genotypes
Using existing variability in senescence dynamics for wheat improvement requires intensive field-testing of large populations in contrasting environments
Summary
Maximizing carbon assimilation by a prolonged green leaf area duration after anthesis is a major breeding aim in many crops This so-called stay green (Thomas and Smart, 1993) has been linked to increased grain yield (GY) in several crops (reviewed by Gregersen et al, 2013). Stay green results from a delayed onset of senescence and/or a reduction in the rate of the process (Gregersen et al, 2013). The benefit of such an extended period of functional stay green, i.e. a prolonged. Finetuning senescence dynamics has been proposed as a promising selection criterion in wheat breeding under the scenario of an increased frequency of weather extremes, such as heat and drought
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