Does Leaf Waxiness Confound the Use of NDVI in the Assessment of Chlorophyll When Evaluating Genetic Diversity Panels of Wheat?

Kamal Khadka,Alireza Navabi,Hugh J Earl,Manish N Raizada,Andrew J Burt

doi:10.3390/agronomy11030486

Abstract

Ground and aerial-based high throughput phenotyping platforms (HTPPs) to evaluate chlorophyll-related traits have been utilized to predict grain yield in crops including wheat (Triticum aestivum L.). This study evaluated chlorophyll-related and other physiological and yield traits in a panel of 318 Nepali spring wheat genotypes, termed the Nepali Wheat Diversity Panel (NWDP). Field experiments were conducted using an alpha-lattice design in Nepal and Canada. Chlorophyll-related traits were evaluated with a Soil Plant Analysis Development (SPAD) meter and the normalized difference vegetation index (NDVI) using a handheld GreenSeeker and an Unmanned Aerial Vehicle (UAV). Relative leaf epicuticular waxiness was recorded using visual assessments. There was a significant positive association (p < 0.001) between waxiness and SPAD-based chlorophyll estimates, and both of these traits displayed a significant positive relationship with grain yield. However, unexpectedly, NDVI derived from both GreenSeeker and UAV was negatively associated with waxiness and grain yield. The results obtained after segregating the trait means into groups based on waxiness scores and breeding history of genotypes indicated that waxiness along with precipitation could be affecting the multispectral reflectance. These results suggest that caution should be taken when evaluating a large and diverse wheat population for leaf chlorophyll using high-throughput NDVI methods.

Highlights

Published: 5 March 2021Wheat (Triticum aestivum L.) is the source of ~20% of global calories [1], demonstrating its importance for global food security
This study focuses on one unexpected result, Agronomy 2021, 11, 486 namely a negative association between normalized difference vegetation index (NDVI) and leaf wax, which has implications for the use of NDVI for measuring leaf chlorophyll in wheat diversity panels
The results showed a significant positive association between grain yield (p ≤ 0.0001) and AUSC (r = 0.40), and grain yield and waxiness (r = 0.49) (Figure 1)

Summary

Introduction

Wheat (Triticum aestivum L.) is the source of ~20% of global calories [1], demonstrating its importance for global food security. As the world’s population is approaching ~10 billion in the 30 years [2], wheat breeders have a tremendous challenge ahead to develop high yielding wheat varieties at a greater pace. As a consequence of climate change, factors such as drought can hinder or reverse progress in improving wheat grain yield [3]. The intensity, frequency, and duration of drought [4] along with the growth stage at which the drought events occur [5] are responsible for losses in grain yield. Understanding the physiological traits associated with stress tolerance plays a critical role in generating new high-yielding, climate-resilient wheat varieties [7,8,9]

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