Although the effect of stress conditions on the qualitative characteristics of the produced seeds such as the vigor index is known; however, changes in the appearance of seeds under the influence of these stresses have not yet been properly investigated. Therefore, based on image analysis (photographed with a stereo microscope using Mosaic 2.1 software), the effect of sowing date and deficit irrigation on morphological characteristics and quality of quinoa seed (Chenopodium quinoa Willd.) under the semi-arid region of Mashhad, Iran, was investigated. The experiment was conducted in the form of split plots in a randomized complete block design with three replications; sowing dates (July 6, July 23, and August 6) and deficit irrigation regimes (7-, 14- or 21-day irrigation return period) were the main and secondary factors of the experiment, respectively. According to the results, severe drought stress increased the leakage of electrolytes and mean germination time (MGT); while the seed yield, germination percentage, seed area, embryo length, and cotyledons were decreased. Also, the assessment of the appearance of the seeds showed that the imposition of stress increases the wrinkling of the seeds. In addition, the highest ion leakage (107.69 μS cm−1 g−1) and MGT (1.29 day) were observed in July 6 sowing treatment along with the lowest seed weight (1.83 mg), seed area (2.92 mm2), and seed yield (3098 kg ha−1). Moreover, a negative and significant correlation was recorded between seed area and vigor indexes such as MGT and electrical conductivity. As a suggestion from the test results, the output of image analysis in terms of functional morphology, such as the appearance of the seed and the ratio of embryo to cotyledon, can be an accurate criterion to measure the stresses imposed on the mother plant during the growing season.

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