On the use of spectral reflectance indices to assess agro‐morphological traits of wheat plants grown under simulated saline field conditions

Abstract

Successful breeding of plants for salinity stress tolerance requires realistic growing conditions and fast, non-destructive evaluation techniques for phenotypic traits associated with salinity tolerance. In this study, we used subsurface water retention technique (SWRT) as a growing condition and spectral measurements as an evaluation method to assess different agro-morphological traits of salt-tolerant (Sakha 93) and salt-sensitive (Sakha 61) wheat genotypes under three salinity levels (control, 60, and 120 mM NaCl). The effects of salinity on agro-morphological traits were evaluated and related with forty-five published vegetation-and water-spectral reflectance indices (SRIs) taken at both the heading and grain milk growth stages for each salinity level, genotype, and growth stage. In general, the agro-morphological traits gradually decreased as salinity levels increased; however, the reduction in these traits was more pronounced in Sakha 61 than in Sakha 93. The effect of salinity levels and their interaction with genotypes on the SRIs was only evident at the grain milk stage. The performance of the spectral reflectance indices depicted that the closest associations with agro-morphological traits depended on salinity level, degree of salt tolerance of the genotypes, and growth stage. The SRI-based vegetative indices correlated better with growth and yield of Sakha 93 than SRI-based water indices and vice versa for Sakha 61. The SRI-based vegetative and water indices are effective for assessment of agro-morphological traits at early growth stages under high salinity level. The functional relationship between grain yield per hectare and the best SRIs was linear for the high salinity level and Sakha 61; however, the quadratic model was found to best fit this relationship for the control, moderate salinity level, and Sakha 93. The overall results indicate that the usefulness of the SRIs for assessment of traits associated with salinity tolerance is limited to salinity level and growth stage.

Ability of Modified Spectral Reflectance Indices for Estimating Growth and Photosynthetic Efficiency of Wheat under Saline Field Conditions

“…There are few studies have investigated the performance of spectral reflectance indices (SRIs) for detecting the variations of these parameters under realistic saline field conditions. El-Hendawy et al [25] and Hackl et al [37] reported that, in salinity studies, the growth platform may impact on the use of spectral measurements to assess the phenotypic parameters and in the exploration of the importance of high-throughput phenotyping technique for evaluating salinity tolerance. Hackl et al [36] found that the relationships between SRIs and phenotypic parameters under simulated close-to-field conditions were more robust compared with the results of pot-grown plants conditions.…”

“…Salt-tolerant (Sakha 93) and salt-sensitive (Sakha 61) spring wheat cultivars [25,27] were used in this study. The two cultivars were grown during the 2016/2017 and 2017/2018 growing seasons at the Dierab Research Station of the College of Food and Agriculture Sciences, King Saud University, Saudi Arabia (24 • 25 N, 46 • 34 E; elevation 400 m).…”

“…Various changes in biophysical and biochemical characteristics of the canopy (such as leaf chlorophyll and other photosynthetic pigments contents, leaf tissue structure, dry matter accumulation, photosynthetic efficiency, and plant water status) have been found to be change in relation to osmotic and ionic components of salinity stress, and these cause noticeable variability in the spectral reflectance of the canopy in the three parts of the spectrum (VIS, NIR, and SWIR) domains [4,21,25,26]. Therefore, several SRIs that incorporate wavelengths related to the abovementioned main physiological characteristics of plants were modified to indirectly estimate the growth and photosynthetic efficiency of crops under various environmental conditions.…”

“…For example, Poss et al [23] found that the water band index (WBI = (R 900 /R 970 )), which incorporates one of the water absorption bands from the NIR region (970 nm), reflects the response of wheatgrass growth (Agropyron elongatum L.) to salt stress. In addition, El-Hendawy et al [25] reported that SRIs combining the NIR and SWIR wavebands are suitable for assessing the growth of spring wheat under salt stress, and SRIs incorporating the NIR band (1321 nm) and SWIR band (2264 nm) was found to be important for assessing responses of the growth of cotton plant to salt stress [26].…”

Hyperspectral reflectance sensing to assess the growth and photosynthetic properties of wheat cultivars exposed to different irrigation rates in an irrigated arid region

“…Hyperspectral reflectance sensing technique has been demonstrated to be a valuable and powerful alternative to traditional methods for the simultaneous indirect assessment of hundreds of morphophysiological parameters in a rapid, non-destructive, and consistent manner under different abiotic stresses [ 1 , 19 – 24 ]. Such technique is based on the capabilities of plants to reflect and absorb the light or solar radiation at the visible-infrared (VIS, 400–700 nm) the near-infrared (NIR, 700–1300 nm) and the shortwave-infrared (SWIR, 1300–2500 nm) wavelengths depending on biophysical and biochemical characteristics of the canopy, which are sensitive to water deficit stress.…”