Factors Affecting Seed and Stem Cutting Propagation of Stevia rebaudiana (BERT.)

Abstract

Stevia rebaudiana (BERT.) is a very remarkable plant that is starting to gain ground in the United States. Stevia rebaudiana has been used in numerous countries for thousands of years as a source of sweetener that is all natural and will not raise a person’s glycemic index, which is especially important for diabetics. Propagation of Stevia rebaudiana is problematic with low seed germination rates and limited research done in the United States. Stevia rebaudiana has potential to be a prominent crop in the southern United States but growers need to know how to produce the plants efficiently as the demand for natural products continues to rise. The main objective of this work was to identify specific methods of propagation for Stevia rebaudiana using readily available materials to produce healthy transplants can be grown. Seed germination for Stevia rebaudiana is typically poor with seeds planted right after harvest, due to a variety of reasons, such as: low viability; fungus produced on pappus bristles of seed coats; and poor pollination in some areas. Little literature is available on Stevia rebaudiana seed propagation. In Chapter 2, 3 experiments looking at seed germination with light or without light, in 4 substrate types were completed. Substrates of 50% pine bark:50% peat moss, 100% sand, 100% perlite, and 100% vermiculite by volume were evaluated. Cell pack trays with poly lids either blacked out or left clear were used. Under no-light conditions 100% vermiculite and 100% perlite performed best for germinating Stevia rebaudiana seeds. One hundred percent sand:light had maximum germination rates at 14 days after seeding (DAS). Fungal growth on the 50% pine bark:50% peat moss substrate and substrates such as 100% vermiculite:light led to the lowest germination rates. Seeds germinated under both light conditions and therefore 100% sand:light is recommended since most growers germinate seeds in a greenhouse under light conditions. Stevia rebaudiana can be 250 to 300 times sweeter than sucrose with no calories. Propagation is usually done by stem cuttings due to seed propagation usually having low germination rates. To produce transplants needed for increasing production demand, more efficient propagation techniques are being tested in order to increase plant production. In a second study stem cutting propagation in the Southeastern Unites States was evaluated (chapter 3.) This asexual propagation study looked at stem cuttings and the effect that substrate and cutting type played. The stem cuttings were taken from container grown stock plants and planted in 32 cell packs with one cutting per cell. The two node cuttings were placed in one of 4 types of substrates: 1:1 pine bark:sand by volume, 1:1 peat moss:perlite by volume, 100% sand, or 1:1 sand:vermiculite by volume. Two cutting types were evaluated, medial and terminal. Stem and cuttings were placed under mist for 15 seconds every 10 minutes for the first 4 weeks, then 5 seconds every 10 minutes the remaining 4 weeks of the studies. Data analyzed included: foliar color rating of both old and new foliage, shoot breaks over 2.54 cm (1 inch long), and root length was also looked at. No interactions were found between substrate and cutting type were found. Greatest root length occurred in the 1: sand to 1: vermiculite substrate while 1:1 part pine bark:sand substrate had a greater root length. Medial cuttings had more shoot breaks than terminal cuttings regardless of the substrate used. When looking at old and new foliage, medial cuttings had a greater color rating than terminal cuttings on a rating scale of 1-5 (scale of 1-5 with 1-dead, 3-yellow, 5-dark green). Pinebark:sand or sand:vermiculite would be recommended for use as substrates for liners as root length and new growth are important factors in producing liners. Removing apical dominance in liners is also recommended.