Effects of melatonin and ascorbic acid foliar application on grain yield and mucilage of Plantago ovata Forssk.

Ascorbic acid and melatonin as the biostimulants affect the biosynthesis of phytohormones, facilitate and increase the nutrients uptake, enhance the defense mechanisms, stimulate the root growth, and finally, increase the quality and quantity of the product by affecting the plant metabolites. This study was conducted in a randomized complete block design with three replications to investigate the effects of foliar application of melatonin and ascorbic acid on the grain yield and mucilage content of Plantago ovata Forssk. in the research greenhouse of Bardsir Faculty of Agriculture, Shahid Bahonar University of Kerman in 2020. The experimental treatments included the foliar application of distilled water (control), melatonin 100 μM, ascorbic acid 100 μM, and melatonin 100 μM + ascorbic acid 100 μM. The foliar application treatments continued from the time of complete establishment of seedlings (3-4 leaves) to the physiological maturity stage of seeds (four times every two weeks). The results showed that the foliar application of melatonin and ascorbic acid (single and combined application) enhanced the number of tillers per plant, number of spikes per plant, spike length, number of seeds per spike, and 1000-seed weight significantly. The highest grain yield was obtained from the foliar application of melatonin (59.98 g.m-2) and melatonin + ascorbic acid (61.85 g.m-2) without statistically significant differences with each other. The ascorbic acid foliar application also significantly increased the grain yield by 6.61% compared to the control. The foliar application of ascorbic acid, melatonin, and melatonin + ascorbic acid increased the mucilage content by 12.29, 19.89, and 23.80%, respectively compared to the control. The application of melatonin alone or in combination with the ascorbic acid, without statistically significant differences with each other, had the greatest positive effect on increasing the mucilage percentage. The mucilage yield was obtained 10.03, 13.47, 14.94, and 15.64 g.m-2 in the control, ascorbic acid, melatonin, and melatonin + ascorbic acid treatments, respectively. Based on the results, it can be concluded that the foliar application of melatonin and ascorbic acid could improve the quantitative and qualitative yield of P. ovata, and among the treatments their combined application was more effective.