Effect of potassium humate on morphological traits and phytochemical composition of periwinkle (Catharanthus roseus (L.) G. DON) medicinal plant

Background and objectives: Periwinkle (Catharanthus roseus (L.) G. DON) belongs to the plant family Apocynaceae and is cultivated in many countries around the world. Over 130 indole alkaloids, collectively termed terpenoid indole alkaloids, have been extracted from periwinkle, including the most significant and potent anticancer products vincristine and vinblastine. Soil nutrient elements are especially important for improving the growth and development and quality of medicinal plants. This importance is due to the fact that soil nutrients can be managed and changed, and by adjusting and improving them, the quantity and quality of medicinal plants can be improved. In this regard, sustainable agriculture, emphasizing the balanced use of organic and biological fertilizers, provides an effective solution for increasing the production of agricultural products and maintaining the stability of soil fertility, sustainable and high-quality production. Potassium humate (KH) is natural biological organic nutrient, highly affecting physio-biochemical properties of soil and the productivity of plants. Humic materials derive from the chemical and biological humification of animal and plant matter through the biological processes of microorganisms. These substances impact plant performance and soil fertility by an increase in the soil microbial content stimulating the soil productivityby enhancing the soil-root cation exchange capacity.

Methodology: The study aimed at investigating the influence of potassium humate on morphophysiological traits and phytochemical compositions of periwinkle. It utilized a randomized complete block design (RCBD) with three replications during two consecutive growing seasons, 2022 and 2023, in Medicinal herbs garden of Agriculture Research and Training Center, Hamadan. The experiment included five varying doses of potassium humate including 0, 2.5, 3, 3.5, 4 g.m-2 applied through fertigation. The aerial parts and roots were collected during the blooming period (end of August and mid-September). Morphological traits, such as plant height (from the crown to the tip of the main stem) and root length, were measured using a ruler in each replication, and then averaged. The number of flowers and fully grown leaves on each plant was tallied until the end of the growth cycle. To ascertain the fresh and dry weight of the above-ground portions, the plants were severed from the soil surface and weighed using a digital scale. Subsequently, the plants underwent a 72-hour drying process in an oven set at 60 degrees Celsius. Once their weight had reached a stable point, they were weighed again. Also the investigated, physiological and biochemical traits included leaf chlorophyll, proline, flavonoid, total phenol, and antioxidant activity in the leaves of this plant.

Results: The effect of potassium humate on flower and leaf numbers, root and stem length, fresh and dry plant weight, chlorophyll, proline, phenol, flavonoid content, and leaf antioxidant activity was significant (p<0.05). Moreover, the year had a notable impact on all these factors except chlorophyll and leaf phenol (p<0.05). The interaction effect of treatment × year on flower numbers, total plant dry weight, and chlorophyll a was also significant (p<0.05). The findings demonstrated that the Potassium humate treatment (4 g.m-2) yielded the highest average count of flowers and leaves, stem and root length, fresh and dry weight of the entire plant, chlorophyll a, chlorophyll b, total chlorophyll, antioxidant activity, phenol, and leaf flavonoids. Conversely, the control treatment displayed the lowest results. The largest quantity of proline was associated with the control treatment. In the second year, applying treatments significantly improved the characteristics of the periwinkle plant. Notably, there was a marked increase in the number of flowers, leaves, stem length, total fresh and dry weight, as well as antioxidant and flavonoid activity in the leaves. Root length, on the other hand, was mainly affected by treatments in the first year. Examination of the treatment-year relationship showed the highest flower count (13.77), whole plant dry weight (55.33 g), and chlorophyll a content in the second year with a potassium humate level of 4 g.m-2.

Conclusion: Overall, applying 4 g.m-2 of Potassium humate showed the most significant effect on the morpho-physiological and phytochemical composition of periwinkle plants in the second year. Consistent use of Potassium humate as an organic fertilizer had a positive impact on these characteristics during the entire growth period. The aim of the study was to replace mineral fertilizers with organic and biological fertilizers to improve nutrient uptake, plant growth and phytochemical compositions of periwinkle.