How do sowing time and plant density affect the pigments safflomins and carthamin in florets of safflower?

Abstract

Safflower (Carthamus tinctorius L.), a multipurpose plant grown in many areas of the world primarily for oil extraction from seeds for food and industrial application, recently has been drawn attention as a source of natural colourants. A two-year study was carried out to examine the combined effects of sowing time (24 February, 28 March, 26 April, in 2017; 21 February, 28 March, 24 April, in 2018) and plant density (25 and 50 plants/m2) on florets and pigments (safflomins and carthamin) production in safflower (cv. Catima) in a semi-arid Mediterranean environment. Sowing delay from February to April led to a significant decrease in heads and florets yield. Indeed, crop growth period was shortened as sowing time was delayed, since flowering occurs when photoperiod requirements are fulfilled (photoperiodic control) irrespective of thermal time. Single plant was more productive at low plant density. However, heads production per unit area was greater at high plant density, i.e. increased plant population overcompensated for heads losses at individual level, irrespective of sowing time. Early sowings also resulted in a higher content of safflomins (up to 54.6 g/100 g) and carthamin (up to 2.97 g/100 g) in florets. Negative relationships described for both pigments vs. air temperatures reveal how their content tends to decrease with the raise of temperature during flowering. Plant density had no relevant effect on pigments content. Further research on the effects of the agronomic management on pigments production of safflower may help to promote the expansion and development of this still underutilized but economically important crop.