Biochemical and cytological features of onion bulbs and leaves collected from various ecogeographical origins

Allium cepa L. genotypes with different ecogeographical origins revealed the highest nutritional values when grown in Crimea, Russia. However, their environmental adaptation should be further investigated. This research was performed during 2016–17 to evaluate the qualitative, antioxidant, and mineral composition characteristics of 15 onion genotypes, of which four originated from the Federal State Budget Scientific Institution, Research Institute of Agriculture, Crimea, Russia. Sweet onion genotypes exhibited high ascorbic acid contents of 11.8–27.3 mg/100 g. However, some genotypes had a narrow range of ascorbic acid content (11.8–21.1 mg/100 g) due to their different ecogeographical origins and proved to be appropriate for industrial processing because of their spicy taste. Intensely colored bulbs had a high content of polyphenols (anthocyanins), which are known to have a positive influence on human health. Electronic microscopic assays revealed the morphological characteristics of A. cepa L. genotype leaves and demonstrated the differences in epidermal structure and adaptability potential. The 12 main mineral macro- and microelements with the highest contents in onion leaves were analyzed. The hyperaccumulator genotype with the highest leaf macro- and microelement content could be used to address mineral element deficiencies in humans. In onion genotype leaves, the contents of the mineral elements followed the order of Zn > Fe > Si > Na > Р > Cl > Mo > Mg > S > Ca > Cu > K. The biochemical analysis of 13 onion cultivars showed that the majority exceeded the standard values of dry matter and sugars (mono- and disaccharides) by 13% and 46%, 11% and 48%, and 36% and 150%. In onion genotypes, leaf surface microstructure was specific, and the largest stomata corresponded to the most productive cultivars.