Association Between Water Spectral Indices and Plant Water Status in Spring Wheat Under Water Stress Conditions.

Several water indices were determined to establish their relationship with water potential and other parameters related to plant water content in spring wheat lines under water stress field conditions. Diverse advanced breeding lines from the International Maize and Wheat Improvement Centre (CIMMYT) were employed that corresponded to five trials: a subset of sister lines including parents (SBS-I and SBS-II), lines selected for high water use efficiency (WUE-I and WUE-II), and synthetic derivatives (SYNDER) selected for high grain yield under drought conditions. All genotypes were planted at CIMMYT’s experiment station in Northwest, Mexico during three growing seasons (2006, 2007, and 2008). Five water indices (WI and four NWIs; water index and normalized water indices, respectively) were determined at diverse growth stages using a field portable spectrometer (ASD, CO). The relationships between the normalized water index three (NWI-3) and the water potential were significant for the WUE-I, WUE-II, and SBS-II trials when both parameters were correlated in individual growth stages. However, when growth stages were combined (booting, anthesis and grain filling), the relationships between the NWI-3 and water potential were stronger for the SBS-II (r²=0.85) and SYNDER (r²=0.76) trials in the year 2008, explaining large proportion of the water potential variations. Similarly, the canopy temperature showed strong association with the water indices (r²=0.81 and 0.78 for SBS-II and SYNDER, respectively) as well as for water potential (r²=0.61 and 0.72 for SBS-II and SYNDER, respectively) combining midday determinations. The SBS-II and SYNDER genotypes showed the stronger relationships of the NWI-3 with water potential, canopy temperature, grain yield, and biomass. In addition, they showed high relationships between the NWI-3 and soil moisture. Apparently, resistant genotypes with high water content, high grain yield, and low canopy temperature could access to deeper soil layers for water uptake.