Estimation of protein content in wheat grains under different irrigation regimes via vegetation indices

Biotic and abiotic environmental factors during the production of bread wheat (Triticum aestivum L.) directly affect the yield and quality of the grain. Climatic factors are the most significant in the definition of yield, contributing to the greatest variability compared with genotype. This influence is also present in the quality characteristics that the bakery industry seeks, such as the protein content in grain and flour. These characteristics can be estimated during the production stage via vegetation indices. Therefore, the objective of this research was to identify the correlations between the vegetation indices, normalized differential vegetation index (NDVI) and green leaf index (GLI) with the total protein content, as well as with the yield components and characteristics of bakery and industrial quality, in flour wheat genotypes under different irrigation conditions. The NDVI was estimated each week during the grain filling period. To obtain the GLI, orthophotos were constructed from scheduled flights with an unmanned aerial vehicle (UAV) during the same period. Twentyfour genotypes of bread wheat were evaluated, of which 18 were commercial varieties and 6 were experimental lines, under four irrigation treatments: 0-55, 0-45-75, 0-45-75-100 and 0-35-75-85-105 d after sowing. The results revealed a significant positive correlation between the grain protein content and the NDVI and a highly significant correlation with the GLI. This correlation was more evident under contrasting irrigation conditions. Therefore, the GLI index obtained at the grain-filling stage can be used as a predictive tool to estimate the protein content in harvested grains.