Foliar treatment with proline and tyrosine affect the growth and yield of beetroot and some pigments in beetroot leaves

There is interest in increasing the yield and pigment content of beetroot and red beet since conventional agronomic practices or breeding efforts have not produced satisfactory results. Using a local cultivar of red beet (Beta vulgaris L. subsp. cicla) as the model plant, pot experiments were established to determine the effects of proline and tyrosine (used as plant growth regulators and for synthesis of beetroot pigments) on growth and yield and pigment (carotenoids and chlorophyll) levels in leaves. Proline or tyrosine at 100 and 200 mg·L^-1 increased plant height, number of leaves, fresh and dry weight of leaves and roots, root/shoot ratio, and root diameter and length while a higher concentration (400 mg·L^-1) increased some parameters but decreased others. Any proline concentration resulted in more leaf carotenoids and chlorophyll and higher carbohydrate content in leaves and roots than the controls, and tyrosine was more effective than proline. Tyrosine and proline proved to be successful agents in improving growth and yield characters of beet plants, especially at 100 mg·L^-1 and 200 mg·L^-1. Beetroot growers can effectively use these two amino acids as a foliar application to increase yield for edible purposes and to increase pigments for extraction for use in coloring and medicinal industries.