Morpho-physiological and Yield Responses of Quinoa Genotypes (Chenopodium quinoa Willd) to the Application of Potassium and Zinc Chelates under Drought Stress Conditions

Since the development of crop cultivation and their yield depend on irrigation and since drought is one of the features of our country, one of the solutions to deal with these problems is the implementation of applied research in the field of stress-resistant plants cultivation such as quinoa. Also, considering the important role of potassium and zinc elements in the plant, providing a sufficient amount of these elements under drought stress can be effective in increasing the plant's resistance to this type of stress. Considering the genetic differences of plants and their different reactions in the face of environmental stress such as drought stress, and different fertilization of genotypes, it seems necessary to carry out this research to investigate the application of potassium and zinc chelates on the morpho-physiological and yield indicators of three quinoa genotypes under drought stress conditions in Razavi Khorasan climate.

This study was conducted to study the morpho-physiological and yield responses of three quinoa genotypes to foliar application of zinc and potassium chelates under drought stress conditions in a research educational farm - Faculty of Agriculture of Islamic Azad University, Mashhad branch located in Golbahar during two crop years 2018-19 and 2019-20. The experiment was a factorial split plot in the form of a basic randomized complete block design with three replications. Drought stress at four levels as the main plots (normal irrigation as a control treatment, 75% of crop capacity, 50% of crop capacity, and 25% of crop capacity) and as the sub-plots, the combination of quinoa cultivars at three levels (Q26, Q29, and Titicaca) and foliar spraying were tested at four levels (no foliar spraying as a control, 100% zinc chelate, 100% potassium chelate and 50% combination of zinc and potassium chelates). Planting was done in the middle of May in both years. To measure the photosynthetic pigments after 10% flowering, sampling was obtained from the young terminal leaves separately from each plot. Analysis of the obtained data was done using SAS 9.2 software. The mean comparison of the evaluated traits was done using Duncan's multiple range test at 5% probability level.

The growth and yield indicators and photosynthetic pigments decreased with the increase in stress intensity. Results also showed that the combined foliar spray treatment resulted in higher height, plant weight, number of seeds per spike, seed, and biological yield than other fertilizer treatments. Although different varieties had different reactions to different traits, the highest plant weight, number of seeds per spike, thousand seed weight, seed yield, and chlorophyll a and b were obtained in the Q26 variety. The highest plant height and biological yield were obtained in the Tricaca variety and combined foliar application under non-stressed conditions, and for plant weight, number of seeds per spike, seed yield, and chlorophyll b traits were observed in the G26 variety and combined foliar application under non-stressed conditions. Also, the highest amount of harvest index and chlorophyll a were obtained in the treatment without stress and Q26 variety and 100% Zn foliar application. On the other hand, the highest 1000 seeds weight and carotenoids were obtained in 100% K foliar application and Q26 and Tricaca cultivars under no stress, respectively. In the second year of the experiment, the growth and yield of the plant increased significantly compared to the first year under different levels of irrigation and also different levels of foliar spraying.

In general, in this experiment, the yield of the quinoa plant is reduced by reducing the amount of water consumed and as a result, the occurrence of drought stress, but with the use of foliar spraying, especially combined foliar spraying, the adverse effects of drought stress on the performance of this plant can be reduced to an optimal extent. It seems that in the region in question, the difference in rainfall and evaporation, and transpiration in the two years of the experiment had a significant effect on the studied traits so that in the first year compared to the second year, the limitation of water resources was more effective in reducing plant growth and yield. However, using appropriate amounts of combined and separate foliar spraying to increase the plant's ability to absorb water more effectively is a suitable method to increase the yield of different quinoa cultivars under drought stress.