Rapid Estimation of Canopy Cover in Durum Wheat Using Digital Images.

There is increasing demand for simple, rapid methods to evaluate crop growth under field conditions, especially as a means to assist dissection of interacting effects of genetics, environment and management on crop growth and development.  Simple digital color (RGB) images of crop canopies can be analyzed to estimate canopy cover. We assessed canopy cover using digital images of a diversity panel of 260 accessions of durum wheat (Triticum turgidumDesf.), originally from different countries across the wheat-growing areas, in a 2016 field experiment at Maricopa Agricultural Center in Arizona.  This diversity panel has been previously genotyped using a high-density single-nucleotide polymorphism (SNP) assay.  We manually photographed (Lumix DMC digital camera) each plot at two subsample positions within the plot, using a simple metal A-frame camera stand to ensure a nadir (overhead) view and constant height and hence, field of view.  Approximately 200 images could be recorded per hour. Canopy cover was estimated from each image using a batch script implemented in ImageJ (1.49V), with analysis of 600 images requiring approximately one hour.  Early canopy cover correlated to stand counts (r = .71, p < 0.001 at 34 DAS). Time trends showed large differences among lines for rate of growth and for maximum cover. Minor issues were found with leaves of weeds being included in cover estimates and with variation in lighting. The method shows value as a simple and low-cost option for field-based phenotyping to better understand the impacts of abiotic conditions and climate on genotypes and crops.