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Evaluation of ten genotypes for leaf physiological performance under a simulated heat wave
AdvisorBarrios-Masias, Felipe H.
Environmental and Natural Resource Sciences
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Quinoa (Chenopodium quinoa Willd.) sensitivity to high temperatures is an impediment to adoption in regions prone to heat waves, despite quinoa being a highly resilient crop to a wide range of abiotic stresses. Although reductions in yield due to heat are usually associated with pollen viability, the present study aimed to understand the effects of high temperature on the leaf and its capacity for carbon assimilation. Several trials were conducted with 10 quinoa genotypes classified as being either sensitive or tolerant to heat stress on a previous screening of 112 lines. Plants were grown in the greenhouse at normal temperatures (i.e., control), and at the sixth growth stage were exposed to temperature treatments in growth chambers. The heat treatment simulated heat waves of four consecutive days with temperatures higher during the day and night (Heat: 45/30 ˚C, and Control: 20/14 ˚C). Chlorophyll fluorescence (predawn and day), leaf gas exchange (day) and dark respiration (night) were measured during several experiments. In addition, leaf cell membrane stability was evaluated in the laboratory at temperatures of 47, 51 and 55 ˚C. Results show that most quinoa genotypes under the heat treatment increased their photosynthetic rates and stomatal conductance, resulting in a lower intrinsic water use efficiency. These results were partly corroborated by changes in the maximum quantum yield of photosystem II (Fv/Fm). Dark respiration decreased under the heat treatment in most genotypes. The cell membrane stability assays showed that temperatures of 51 ˚C or higher increased the percent injury to >70%, and a temperature of 47 ˚C may be a better screening temperature as injury was around 35%. These results suggest that heat stress does not affect carbon assimilation capacity, but higher transpiration and lower intrinsic water use efficiency may lead to water deficits and exacerbate plant stress responses, resulting in lower yields.