Influence of harvesting dates and genotypes on secondary metabolites status and antioxidant activity in Lawsonia inermis L. (Henna)

The composition and concentration of bioactive compounds and minerals in henna (Lawsonia inermis L.) can be considerably affected by harvesting date and genotype; whereas, less information is available regarding these factors. This study was performed as a split-plot design based on randomized complete block design (RCBD) with three replications (n = 3). Experimental treatments consisted of three harvest dates (May, July, and October) as the main plot and five genotypes (Kahnooj, Bam, Jiroft, Qale gang, and Zehekalut) as sub-plot over two years of 2019 and 2020. According to results, harvesting dates significantly affected secondary metabolites such as lawsone, flavonoid, tannin (p < 0.01), and antioxidant activity in terms of DPPH (p < 0.05). The interactive effect of harvest date × genotypes indicated that Bam × July recorded the maximum of lawsone (90.56 μg/ml). Additionally, the highest level of phenolic compounds was achieved under the interaction effect of Kahnooj × October (160.1 μg/g Gallic acid/DM). Bam × July × year (2019) showed the maximum of lawsone and flavonoid (94.59 μg/ml and 98.04 μg Catechin/g DM, respectively), also, Bam × October × 2019 produced the highest tannin level (13.03 mg catechin/100 ml E). Furthermore, there was a positive correlation between tannin, anthocyanin, and flavonoid with lawsone, while phenol, antioxidant activity (DPPH, RP) was negatively correlated with lawsone. Regardless of harvest date, the highest lawsone, anthocyanin, and flavonoid content in 2019 was obtained in Bam genotype. Overall, this study suggests that July can be the optimum date for harvesting of Bam genotype regarding to the quality characteristics (lawsone and flavonoid).