The feasibility of thermography as a technique for plant screening aiming at drought-tolerance has been proven by its relationship with gas exchange, biomass, and yield. In this study, unlike most of the previous, thermography was applied for phenotyping contrasting maize genotypes whose classification for drought tolerance had already been established in the field. Our objective was to determine whether thermography-based classification would discriminate the maize genotypes in a similar way as the field selection in which just grain yield was taken into account as a criterion. We evaluated gas exchange, daily water consumption, leaf relative water content, aboveground biomass, and grain yield. Indeed, the screening of maize genotypes based on canopy temperature showed similar results to traditional methods. Nevertheless, canopy temperature only partially reflected gas exchange rates and daily water consumption in plants under drought. Part of the explanation may lie in the changes that drought had caused in plant leaves and canopy structure, altering absorption and dissipation of energy, photosynthesis, transpiration, and partitioning rates. Accordingly, although there was a negative relationship between grain yield and plant canopy temperature, it does not necessarily mean that plants whose canopies were maintained cooler under drought achieved the highest yield.

Non-destructive analysis of photosynthetic pigments in cotton plants - doi: 10.4025/actasciagron.v33i4.10926

The objective of this work was to assess the morphophysiological characteristics and the ionic imbalance in the substrate, roots, and leaves of young oil palm (Elaeis guineensis) plants under different levels of saline stress, following a substrate salinization protocol in which the level of salt was known. Bifid oil palm plants were subjected to different NaCl rates (0.0, 0.5, 1.0, 1.5, and 2.0 g NaCl per 100 g substrate on a dry basis), and their morphophysiological responses were evaluated for a period of 12-14 days. This protocol generated different levels of stress due to the gradients of electrical conductivity and water potential in the saturation extract of the substrate, according to the added NaCl. Based on the rates of real evapotranspiration and leaf gas exchange, the osmotic effect of the salt reflected negatively on leaf temperature, on the chlorophyll content index, and on the chlorophyll fluorescence variables. The increase in Na and Cl levels in the saturation extract culminated with the increasing availability of Ca, K, and Mg in the solution and their accumulation in the leaves. However, the plants poorly absorbed Na and Cl. The obtained results are indicative that, for a better characterization of the osmotic and ionic phases of salinity stress, it is necessary to reduce the applied level of salinity stress and to increase the evaluation period.

Leaf-level carbon isotope discrimination and its relationship with yield components as a tool for cotton phenotyping in unfavorable conditions