There is limited information about the critical period of weed interference (CPWI) in quinoa (Chenopodium quinoa Willd.) and the effect produced by the weed-crop interaction in secondary metabolite accumulation. The objective of the present study was to determine the CPWI and its effect on total polyphenol content in quinoa. The experiments were conducted during two consecutive seasons using a randomized complete block design with 16 treatments consisting of 8 weed growth periods and 8 weed-free growth periods in which weed population and biomass were evaluated; productive parameters, yield components, and total polyphenols were determined in the quinoa crop. Grain number per plant affected yield because of weed interference (P < 0.05), which decreased from 4312 to 162 grains plant-1 in weed growth periods and increased from 181 to 5110 grains plant-1 in weed-free growth periods. Total polyphenol content was affected by stress from weed interference (P < 0.05), which increased from 2.2 gallic acid equivalents (GAE) g-1 to 3.6 mg GAE g-1 in weed growth periods and decreased from 3.6 GAE g-1 to 1.9 mg GAE g-1 in weed-free growth periods, while the population remained constant (P > 0.05). The CPWI was determined between the phenological stages of two true leaves to flowering; therefore, the quinoa crop must remain weed-free between these two phenological stages to rule out production losses greater than 5%.

The impact of herbicide application on the accumulation of secondary metabolites and photosynthesis as stress indicators in the quinoa (Chenopodium quinoa Willd.) crop is unknown. The objective of the present study was to evaluate the effect of two post-emergence herbicides on production, total polyphenol content, and chlorophyll fluorescence in quinoa. The experiments were conducted for two consecutive seasons using a completely randomized block design with seven treatments, including two herbicides and three commercial product rates, as well as a control without herbicide application. Production parameters, yield components, and stress indicators were evaluated. Yield was affected (P < 0.05) by herbicide application in some treatments; control and treatment with only one bentazon application varied from 1851.23 to 1235.03 kg ha-1 , respectively. Yield affected the number of grains per plant (P < 0.05); control and treatment with only one bentazon application decreased yield from 3984.60 to 2040.94 kg ha-1 , respectively. Total polyphenol content and percentage of germination in quinoa grains were not affected by stress caused by herbicide application (P > 0.05). The herbicide fomesafen did not affect the maximum quantum yield, while the herbicide bentazon had a significant effect (P < 0.05) during the application. Three sequential applications of bentazon and fomesafen in the absence of weeds were sufficient to achieve a yield that was equal (P > 0.05) to the control.

Wheat (Triticum aestivum L.) is often affected by abiotic stress such as high temperatures and water deficit. Due to this, grain yield can be reduced by a water deficit and an inadequate grain filling as well as affect synthesis of polyphenolic compounds. The aim of this study was to determine the influence of water deficit on yield in spring wheat cultivars during grain filling stage, and evaluate total polyphenol content in whole wheat flour. Experiments were conducted at two locations during 2016-2017 growing season, using a randomized complete block design with a split-plot arrangement, with 12 treatments consisting of three irrigations levels and four spring wheat cultivars. In Site 1, interaction (P < 0.05) was obtained between water deficit level and cultivar, 'Pantera-INIA CL' achieved highest grain yield (10.5 Mg ha-1), with a well-watered treatment, while 'Lasana' reached lowest grain yield (8.5 Mg ha-1), with a severe water deficit. However, water deficit did not affect significantly (P > 0.05) grain yield in Site 2, and differences were observed only between cultivars (P < 0.05) in a range of 6.1 to 7.1 Mg ha-1. Total polyphenol content was not affected by water deficit, differences were only observed between cultivars in both locations (P < 0.05). However, cultivars showed a higher total polyphenol content in Site 1. Water deficit level did not negatively influence yield of four wheat cultivars evaluated in Site 2. While in Site 1, only yield of 'Lasana' and 'Pantera-INIA CL' was reduced, with severe water deficit.

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