Influence of harvest time and genotype on seed yield, petal yield and carthamidin and carthamin contents, and mineral nutritional content in safflower (Carthamus tinctorius L.)

Abstract

Safflower (Carthamus tinctorius L.) is a versatile oil crop with drought, salinity, and severe temperature tolerance. In 2023, the Botswana government incorporated safflower into the cropping system, being among the 13 crops promoted for food security. The objective of this study was to determine the best genotype and time to harvest safflower petals for optimum petal and seed yield, and carthamidin and carthamin contents. The results indicated that phenological traits [days to emergence (8-12), days to flowering (74-117), days to end of flowering (84-126), and days to physiological maturity (99-157)], vegetative growth [height to first branching (13-34 cm), plant height (67-118cm), and number of primary branches/plant (6-12)], yield components [capitula diameter (10-19cm), number of capitula/plant (11-25), number of seeds/capitulum (13-25), and 1000-seed weight (28-39g), seed yield (1063-2697kg/ha), petal yield (91-117kg/ha)]. The carthamidin content (1-7.5%), carthamin content (0.02-0.05%). The mineral nutritional content [Ca (424-517mg/100g), Mg (273-279mg/100g), K (2214-2328mg/100g), Na (224-228mg/100g), Fe (12-17mg/100g), Zn (2-3mg/100g)]. Proximate variables [moisture content (75-80%), crude fibre (3-5%), crude protein (1-3%), fat content (3-3.4%), ash (5-9%) and carbohydrates (4-10%)]. The results showed that phenological traits (days to emergence, days to flowering, days to end of flowering, and days to physiological maturity), vegetative growth (height to first branching, plant height, and number of primary branches/plant), yield components (capitula diameter, number of capitula/plant, number of seeds/capitulum, and 1000-seed weight), and seed yield had significant genotypic variation. In both summer and winter, safflower genotypes and petal harvest time interacted significantly to influence petal yield, carthamidin and carthamin contents, and dye index. Genotypes and time of petal harvest independently had significant variation concerning safflower petal mineral nutritional content (Ca, Mg, K, Na, Fe, and Zn) and proximate variables xiii (moisture content, crude fibre, crude protein, fat, ash, and carbohydrate). It was concluded that the best genotype to maximise safflower seed and petal yield with high carthamidin and carthamin contents, dye index, mineral nutritional content and proximate variables was Turkey (spineless). It was also concluded that the best time to harvest safflower petals to maximise seed and petal yield with high carthamidin content which has many health benefits was either at the onset of flowering or full bloom. However, the best time to harvest safflower petals to maximise mineral nutritional content and proximate variables was variable and inconclusive.