Evaluation of the Effect of Different Irrigation Regimes on the Accumulation of Some Compatible Osmolytes and the Activity of Antioxidant Enzymes in Quinoa

The high nutritional value of quinoa and its ability to grow under adverse environmental conditions have led to an increase in the area under cultivation globally. Quinoa has attracted particular attention in recent years due to its ability to grow under adverse environmental conditions and its high nutritional value.  Water scarcity stress is one of the non-bioenvironmental stresses that has destructive effects on crops' development and yield. Morphological, physiological, and biochemical reactions of plants to water deficiency depend on several factors, including stress intensity, duration of stress, and plant growth stage. Increased proline content, glycine betaine, total carbohydrates, and decreased yield under water stress conditions have been reported in various quinoa studies. The low cost of growing quinoa and its relatively high price, on the one hand, and the need for low water and adaptation to difficult climatic conditions, on the other hand, have made quinoa cultivation very economical. Due to the lack of water resources in different parts of the country and the fact that few studies have been done on quinoa cultivation in our country, the present study was conducted to investigate the effect of different irrigation regimes on some biochemical parameters and quinoa yield.

An experiment was conducted to investigate the effect of irrigation intervals and amounts on the quinoa's physiological traits and yield at the University of Kurdistan research farm, located in Dehgolan plain. The experiment was arranged in a split-plot scheme based on randomized complete blocks design with three replications. Four irrigation intervals (4, 8, 12, and 16 days) were considered the main factor, and four irrigation levels (100%, 75%, 50%, and 25% of plant water requirement) were considered secondary factors. Giza1 cultivar, which was obtained from the Seed and Plant Improvement Institute, was used for cultivation. Traits such as the content of proline, glycine betaine, soluble carbohydrates, insoluble carbohydrates, catalase activity, peroxidase activity, and grain yield were studied. Data analysis of variance was performed using SAS 9.1 statistical software, and means were compared using the Duncan test at 5% probability level. Excel software was also used to draw the graphs.

The effect of irrigation intervals and levels were significant on all studied traits. The study results showed that by reducing the plant's available water and increasing the irrigation intervals, the amount of proline, glycine betaine, soluble carbohydrates, insoluble carbohydrates, peroxidase activity, and catalase activity were increased, but the grain yield was decreased. Increasing the irrigation intervals from 4 to 8 days did not significantly affect grain yield, but increasing the interval to 12 and 16 days reduced grain yield by 24.4 and 44.8%, respectively. The highest grain yield was observed at full irrigation treatment (1866.5 kg.ha-1) but there was no significant difference with the treatment of 75% of the plant water requirement. The rate of yield reduction in the treatment of 25% of plant water requirement compared to the control was about 56.5%.

The results showed that quinoa produced acceptable levels of yield even under severe drought stress, i.e., when the irrigation interval increases or the water availability decreases. Based on our results, one reason for this is stress reduction mechanisms by the quinoa plant, such as increasing the content of compatible osmolites and increasing antioxidant enzymes' activity.