Abstract
The traditional visual rating system is labor-intensive, time-consuming, and prone to human error. Unmanned aerial vehicle (UAV) imagery-based vegetation indices (VI) have potential applications in high-throughput plant phenotyping. The study objective is to determine if UAV imagery provides accurate and consistent estimations of crop injury from herbicide application and its potential as an alternative to visual ratings. The study was conducted at the Kernen Crop Research Farm, University of Saskatchewan in 2016 and 2017. Fababean (Vicia faba L.) crop tolerance to nine herbicide tank mixtures was evaluated with 2 rates distributed in a randomized complete block design (RCBD) with 4 blocks. The trial was imaged using a multispectral camera with a ground sample distance (GSD) of 1.2 cm, one week after the treatment application. Visual ratings of growth reduction and physiological chlorosis were recorded simultaneously with imaging. The optimized soil-adjusted vegetation index (OSAVI) was calculated from the thresholded orthomosaics. The UAV-based vegetation index (OSAVI) produced more precise results compared to visual ratings for both years. The coefficient of variation (CV) of OSAVI was ~1% when compared to 18-43% for the visual ratings. Furthermore, Tukey's honestly significance difference (HSD) test yielded a more precise mean separation for the UAV-based vegetation index than visual ratings. The significant correlations between OSAVI and the visual ratings from the study suggest that undesirable variability associated with visual assessments can be minimized with the UAV-based approach. UAV-based imagery methods had greater precision than the visual-based ratings for crop herbicide damage. These methods have the potential to replace visual ratings and aid in screening crops for herbicide tolerance.
Highlights
Over the past decade, plant phenotyping has gained considerable attention, as more and more researchers realize that the lack of adequate phenotypic data is the bottleneck to achieve further genetic gains in plant breeding programs [1, 2]
Bentazon herbicide was well tolerated by fababean as there is no significant damage to the crop compared to the untreated hand-weeded check with corresponding higher optimized soil-adjusted vegetation index (OSAVI) values (Figures 4 and 5)
The variable injury symptoms arising from herbicides with different mechanisms of action makes the visual assessments more difficult and increases the subjectivity factor
Summary
Plant phenotyping has gained considerable attention, as more and more researchers realize that the lack of adequate phenotypic data is the bottleneck to achieve further genetic gains in plant breeding programs [1, 2]. Phenotype is the outcome of genotype and environment interaction, so the renewed interest in phenomics is because of the ever-changing climate and the need for breeding more adaptable varieties [3]. This has resulted in an increased requirement for reliable and timely phenotypic data to support crop improvement programs [4, 5]
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