Relationship between growth traits and spectral vegetation indices in durum wheat

Future wheat yield improvements may be gained by increasing total dry matter (TDM) production. Vegetation indices (VI) based on spectral reflectance ratios have been proposed as an appropriate method to assess TDM and leaf area index (LAI) in wheat. This study was undertaken to determine whether VI could accurately identify TDM and LAI in durum wheat (Triticum turgidum var. durum (Desf.) Bowden [= T. turgidum subsp. durum (Desf.) Husn.]) and serve as indirect selection criteria in breeding programs. Total dry matter and LAI were determined from destructive sampling from booting to milk-grain in seven field experiments conducted under Mediterranean conditions. Each experiment included one of two sets of 20 or 25 genotypes. Field reflectance values were collected using a portable field spectroradiometer. Two VI, the normalized difference vegetation index (NDVI) and the simple ratio (SR), were derived from spectral measurements and their predictive value for TDM and LAI was evaluated. The best stages for growth trait appraisal were Stages 65 and 75 of the Zadoks scale. The power of VI for assessing TDM was lower than their predictive value for LAI. The suitability of VI for the assessment of growth traits depended on the range of variability existing within the experimental data. Vegetation indices accurately tracked changes in LAI when data were analyzed across a broad range of different growth stages, environments, and genotypes. However, their value as indirect genotypic selection criteria for TDM or LAI was limited, since they lacked predictive ability for specific environment/growth stage combinations.