Effect of Far-red Light on Saffron (Crocus sativus L.) Growth and Crocin Yields

The production of plants in plant factories supplies stable and very safe products regardless of the weather conditions, but is also associated with significant costs in terms of both the initial investment and ongoing electricity expenses. Therefore, to compensate for these high production costs, it is necessary to produce crops with a high unit price. This research focussed on production of the medicinal plant saffron (Crocus sativus L.), which is considered an expensive spice globally. This bulbous plant of the genus Crocus (family Iridaceae) is traditionally cultivated in Iran, where 93.7 % of the world’s total production is grown (Ghorbani, 2008). The basic component of commercial saffron is the stigma, which contains the yellow-red carotenoid pigment crocin (C44H64O24). Crocin has a wide variety of applications not only in the food industry and as a colourant, but also in medicine (Gazerani et al., 2013), with several reports demonstrating its pharmacological activity, including anti-tumour properties and improved outcomes for alcoholic memory disorder (Shoyama, 2009). The life cycle of saffron can be divided into four stages: formation of the flower buds, flowering, formation of the daughter corms (FD) and development of the daughter corms (DD) (Miyagawa et al., 2015). Traditionally, saffron corms start to produce flowers in autumn following transplantation into the field in late summer. The plants’ leaves continue to grow from summer to winter, with two daughter corms usually forming and enlarging at the base of the shoot on their mother corm at low temperatures in winter. At the beginning of spring, the leaves begin to wither and the enlarged daughter corms are harvested and stored while dormant, during which time they undergo flower bud formation. It is well known that the bulbous plant stores a large quantity of carbohydrates in the bulb, which support root growth, nutrient absorption and differentiation of the flower buds, stems and leaves during its underground life (Ohyama et al., 1986). Consequently, since these carbohydrates may make a large contribution to flowering energy, saffron corms that contain a large amount of photosynthetic products are expected to have higher stigma yields, as indicated by the extremely strong correlation between flowering rate and corm weight (Pharmaceutical Affairs Bureau, 1995). In recent years, light quality (i.e. the spectral composition of light) has been identified as an important environmental factor for plant growth and quality improvement. Photosynthesis occurs under photoirradiation conditions that span a particular range of photosynthetically active radiation (PAR), from approximately 400 nm to 700 nm. Far-red radiation, which is the outside part of the PAR spectrum, is not directly involved in photosynthesis but does induce photomorphogenesis in plants via changes in phytochrome equilibrium. For instance, Lercari (1982) found that far-red light irradiation induced the translocation of carbohydrates from the leaves to the bulb in onion Allium cepa) plants and concluded that carbohydrate accumulation in onions is a phytochrome-mediated response; and Terabun (1978) discovered that there was an interaction between red and far-red light in the enlargement of onion, wakegi onion and garlic (A. sativum) bulbs.