Stevia Breeding

Stevia Crop Information

Stevia (Stevia rebaudiana)

  • Introduction
    • Low-calorie sweeteners are important to the food industry. There is extra value if the sweeteners come from natural sources. One of the currently recognized sources of low-calorie, natural sugar replacements is Stevia rebaudiana Bertoni. The main compounds in stevia are glycosides: steviosides and rebaudiosides, and rebaudioside A (one of the reb fractions) is commonly extracted and available on the ingredients market. These compounds are 250 to 300 times sweeter than sucrose, but they have inherent challenges when used in drinks and food due either to their physical, chemical, or sensory properties.
  • Botany
    • Stevia rebaudiana is an herbaceous perennial in the sunflower family, Asteraceae. It is native to Paraguay, and is grown throughout the world. Production is mainly in east Asia and South America. The shoots, and especially the young leaves of stevia contain natural low-calorie sweeteners. The leaf sweetener content is twice that of the flowers; the stems are lower than the flowers, and the roots have none. The flowers of stevia are hermaphroditic with a 2-lobed stigma and 5 anthers.
    • Stevia belongs to the tribe Eupatorium, and the analysis of chloroplast DNA shows that there has been evolution from a high base chromosome number to a low base chromosome number. Thus, stevia is one of the more adapted species in the tribe.
  • Horticulture
    • Stevia seeds are small and germinate slowly; direct seeding in the greenhouse will result in transplants in 45 to 60 days. Propagation of stevia can also be done with stem cuttings, using 4 internodes per cutting for best results. Propagation is best done in late winter rather than early or late spring. Germination of stevia seeds is commonly less than 50%. Germination speed will be faster on a heating pad set at 40°C for under 24 h, but the total germination percentage will be lower. Thus, breeding progress can be improved (more cycles per year) using methods that promote faster germination (although sacrificing higher germination percentage).
    • Leaf yield in Mississippi was highest from 1 harvest every 180 days, rather than 2 harvests every 90 days or 3 harvests every 60 days. So, research programs needing to take data with fewer labor inputs may want to use just a single harvest at the end of the summer season, rather than 2 or 3 harvests over the summer.
    • Stevia is self sterile, probably due to sporophytic self-incompatibility. Plants produce black and tan seeds. Open pollination results in 0-60% black seeds, controlled cross-pollination results in 86% black seeds, the rest being tan colored. The tan seeds have no germination, but black seeds have 59-86% germination. Thus, stevia breeding programs will need to avoid self-pollination, and use either open-pollination or controlled cross-pollination to produce seeds for breeding and testing. Breeding methods using population improvement or synthetic varieties would be efficient, but not methods using pure lines or inbreds.
  • Production Methods
    • The stevia field can be flat planted and transplants put in on 15″ row spacing.  The field was fumigated prior to transplanting.  Immediately after transplanting, 0.75″ of irrigation was applied to start plants growing and to settle the soil around the roots to prevent the first herbicide treatments from contacting the roots. This will get the crop to form a canopy quickly.  Weeds can became a problem, even with three hand weedings per year.
    • Production is as follows:
      • 1) The seedbed (pH 5.5 to 6.5) should be watered to near the limit for the soil before seeding, and kept at a temperature of 15 to 25 C.
      • 2) Seed the soil bed with: 10 to 15 gr/m2.
        • Thin plants to: 1 plant/16.7 cm2 (600 plants/m2).
        • Seedbed dimensions: 10 m x 1 m with a separation of 50 cm among seedbeds.
        • Approximately 166-170 m2 of seedbed will plant 1 ha of production.
        • The texture of the seedbed should be sandy, with organic material and phosphorus added.
      • 3) Distribute the seeds on the surface. Do not cover them with soil. Apply pressure slightly on the surface using the palm of your hands to attach the seeds to the surface. Stevia seeds need sunlight for germination. It is a photoblastic species, so seeds will not germinate if they are covered by soil.
      • 4) Cover the seedbed with a shade cloth (50%) until the plants are 1 to 2 cm high. The fabric will protect the seeds from wind and desiccation.
      • 5) Day 1 to 4: when watering seed displacement should be avoided. The seedbed should stay moist near the limit of the soil until germination. Water 2 to 5 times/day, watering through the shade cloth to prevent seed displacement.
      • 6) Day 5 to 7: the seeds will begin to germinate.
      • 7) Day 8 to 60:
        • The plants should be 1 to 2 cm high. Raise the shade cloth to 40 cm and water the plants through the cloth 3 times/day.
        • Eliminate any poor-growing stevia seedlings as well as weeds.
      • 8) Day 60 to 90: Plants that are 10 to 15 cm high, with a minimum of 20 leaves and strong branches are ready to be transplanted.
  • Chemistry
    • The sweetness obtained from stevia leaves is due to stevioside and rebaudioside. Stevioside has a bitter aftertaste, making it less suitable for use as a sweetener. Rebaudioside-A is sweet without the bitter aftertaste, so it is the preferred compound for isolation from dried leaves. Stevia glycosides are diterpenoids whose biosynthetic pathways share four steps in common with gibberellic acid formation. It appears that stevia has an altered biochemical pathway that favors the production of the intermediate compounds rather than the final product, gibberellic acid.
    • None of the sweet compounds metabolize in the human body, so they are natural, low-calorie sweeteners. This makes stevia a valuable crop for world agriculture, looking for replacements for sucrose and fructose. Stevia became useful as a sweetener crop when it was commercialized by the Japanese in the 1970s. It is now available on the market as leaves, or powdered extracts for use in the preparation of food and drink.
    • The stevia glycosides are present in different forms in stevia leaves, and have different tastes on the human tongue. Stevioside is 250 to 300 times the sweetness of sucrose, reb-A is 350 to 450 times the sweetness of sucrose, reb-B is 300 to 350 times the sweetness of sucrose, reb-C is 50 to 120 times the sweetness of sucrose, reb-D is 200 to 300 times the sweetness of sucrose, reb-E is 520 to 300 times the sweetness of sucrose, dulcoside-A is 50 to 120 times the sweetness of sucrose, and steviolbioside is 100 to 125 times the sweetness of sucrose.
  • Genetics
    • Both genotype and environment affect the content of steviol glycosides in the stevia crop. Broad-sense heritability was measured for yield and quality of 10 varieties of stevia tested in 1 location with 3 replications. Heritability was high for leaf yield (99.0%), stevioside content (92.8%), and plant height (97.0%).
  • Breeding
    • Cultivar Types
      • A stevia germplasm collection was made from Paraguay for the Institute of Himalayan Bioresource Technology in India. Paraguay is the center of diversity for the crop. India has a large breeding program for stevia, and have introduced several elite varieties.
    • Breeding Methods
      • Stevia is induced to flower by short days, which occurs in September to December in the northern hemisphere, and usually occurs 54 to 104 days after transplanting. Photoperiod sensitivity ranges from 8 to 14 hours requirement for flowering depending on the variety. Flowering can be induced at the 4-leaf-pair stage using 2 short-day cycles. Therefore, seedlings of the stevia accessions of interest can be treated with 2 short-day cycles before transplanting to the field, and they should flower when needed in the intercross blocks for the plant breeding program.
      • Stevia is a relatively new crop for agriculture, but has found an important place due to the recent emphasis on natural low-calorie sweeteners. There is already a significant body of research covering the biology, genetics and breeding of stevia from institutes around the world, including Brazil, Canada, China, India, and the U.S. Progress has been made in areas including seed germination, stand establishment, crop production, shoot harvest, and leaf processing. New varieties have been developed that improve on the performance of previous varieties for yield and steviosides. More importantly, it is possible to reduce the bitter compounds, and increase the sweet compounds through selection.
  • Disease Resistance
    • Disease resistance has been studied for Septoria. A screening method was developed to test for resistance, and stevia clone 598-1 was identified as resistant in both field and greenhouse tests.
  • Seed Companies
    • Baker Creek
    • Botanical Interest
    • Everstevia
    • Germany Seeds
    • Gurney’s
    • Harris Seed
    • Hirt’s Botanical
    • Johnny’s
    • Jung Seed
    • Park Seed
    • RH Shumway
    • Richter’s
    • Seed Buddy
    • Seed Savers
    • Seedway
    • Stevia Store (Eirete I)
    • Stevia Store (Eirete II)
    • Stevia Store (Katupyry)
    • Stevia Store (Morita II)
    • Stevia Store (Morita III)
    • Stevia Store (Native)
    • Stokes
    • Super Sweet
    • Swallowtail
    • Territorial
    • Tradewinds
  • Stevia Organizations