Shock, Clinton C. : Clinton C. Shock, former Research Assistant, Department of Agronomy and Range Science, University of California, Davis, is now Assistant Professor, Louisiana State University, Iberia Livestock Experiment Station, Jeanerette.

Leaves of Rebaudiâ??s stevia , a plant used historically in Paraguay as a sweetener and Rebaudiâ??s stevia : herbal remedy , contain compounds about 250 times as sweet as table sugar . Preliminary trials at the University of California , Davis , natural noncaloric of the have shown that production of one compounds , stevioside , could be equivalent to the sweeteningpower of 28 tons per acre of sucrose . However , much needs to be learned about production.problems before the plant can be grown commercially . Clinton C . Shock The plant , Stevia rebaudiana Bertoni , belongs to the eupatory tribe of the compos - ite family and is native to northeastern Para - guay . It is related to other members of the genus found in the United States and in Cen - tral and South America . The chemicals of interest are stevioside , rebaudioside A , and at least six other sweet compounds that have glucoside groups at - tached to a three - carbon - ring central struc - ture . Stevioside concentrations usually range between 3 and 10 percent of the leaf dry weight ; rebaudioside A is less concentrated , 1 to 3 percent . ranging from Stevioside has also been of interest as a source of gibberellins , plant growth hor - HOCH , OH mones , most of which are not availablecom - mercially . The glucosidegroups are removed HQ from stevioside to yield steviol . Modified or normal steviol has been placed in the growth medium of Gibberellafujikuroi mutants to produce several gibberellic acids . Gibberellic OH H GA , , , , is known to occur naturally in acid , stevia leaves but not in commercial quanti - ties . H Possible health risks from human con - of the various compounds in Stevia sumption Stevia contains chemical compounds 250 times as sweet as sugar . Of special interest are rebaudianaare compounds that have glucoside groups attached to a three - carbon - ringcentral structure . not well defined and are being studied by others . lering at the plant base . In the wild it repro - Occurrence of stevia on acid , infertile Climate and growth duces by seed , crown division , or rooting of sandy or muck soils with ample supplies of In northeastern Paraguay , stevia popula - branches that lodge or are trampled by cattle . water is consistent with observations of plant tions have been found in the watershed of the Production of viable seed is erratic . Most of performance under cultivation . Frequent 650 feet . Ypane River at an elevationof about the plants alive in the wild are survivors from shallow irrigations apparently are needed , Grazing , harvesting , and transplanting of plants present the previous year . and the plant has poor tolerance of water stevia to cultivated areas has reduced its stress . The plant has little salt tolerance , so it Cultivation natural occurrence . Plants occur naturally on should not be grown in saline soils or with the edges of marshes or in grassland com - When stevia is cultivated in or near its nat - poor quality water . Most agriculturalsoilsare munities on soils with shallow water tables . ural habitat , it is much more vigorous than in more fertilethan soils where the plant origin - All sites are continuously moist but not sub - natural populations , reaching 3 feet or more so fertilization requirements are ated , ject to prolonged inundation . The soils are in height . Branching and tillering are also expected to be minimal . In Korean experi - typically infertile acid sands or muck . The ments , leaf yield increases resulted from much more profuse . The plant requires fre - as semihumid climate can be characterized quent irrigation and competes poorly with moderate applications of nitrogen , phos - subtropical with temperature extremes from weeds . Currently stevia is under experimental phorus , and potassium fertilizers . 21 O to 110 ° F.Average annual temperature is Poor germination in cold weather , slow cultivation in Brazil , Japan , Korea , Taiwan , 75 O F , and rainfall about 55 inches per year . initial seedling growth , and greater yields by and Southeast Asia , as well as in Paraguay . In competition with natural vegetation , Little is known about cultural practices early planting have led producers in Korea stevia is a slender perennial herb growing to that would allow efficient commercial culti - and other temperate regions to start plants in - 24 inches tall . The plant remains vegetativein vation of this crop in California . The partial doors and then transplant outside in early the spring through early summer and flowers information available from other areas is spring . Seeds germinate better when given in the late summer and fall as a short - day useful . Also some of the physiologicalrequire - light and warm temperatures , but plants are plant . Shoots usually die after maturing or ments and agronomic potential can be de - more productive when seedlings or rooted are frosted off ; new growth comes from til - duced from the plantâ??s origin . cuttings are set out as early as possible in the 4 CALIFORNIA AGRICULTURE.SEPTEMBER - OCTOBER1982 yielded a total of 200 grams per square meter reproductive cycle in November before seed spring . Plants will overwinter in Davis , Cali - when clippedthree times during the season to development was completed . fornia , and may be grown as a perennial . a height of 2 inches . The plants clipped at 2 The 18 lines were clonally propagated to Short days promote flowering . In its native inches had a very low survival rate after the compare productivity of the surviving lines habitat at 21O to 22 â?쳌 S latitude , plants start first clipping , and dry matter yields dropped and to collect information on harvesting the flowering from January to March , equivalent off precipitously . plants for leaf production . Cuttitlgs were to July to September in the northern hemi - Stevia grown at Davis gave the greatest taken from different parts of the plant to sphere . Subsequentfloweringsoccur in rapid yields when harvested only once at the end of determine the best parts for vegetativepropa - as regrowth from the plant crown succession of 900 grams dry the growing season . Yields gation . Cuttings were made from the growing grows shorter each time until winter in July . matter per square meter appear to be possi - tips of branches , the second 3 - inch segment Long days favor leaf yields and leaf stevio - ble . If this yield consists down the branch , or other parts of the plant of 40 percent leaf , side contents . Consequently , plant growth in top , These cuttings were kept separate by 7 percent stevioside , temperate areas with long summer days and if the leaf contains clone and plant part , and success of rooting would be ideal for high stevioside yields , but there would be 25 grams of stevioside per and vigor of rooted cuttings were measured . seed production would be difficult . square meter , the sweetening equivalent of In itsregion 6.3 kilograms per square meter of adaptation , steviacompetes of sucrose . All plant parts from all clones rooted suc - with other small plants adapted to infertile cessfully under mist . Cuttings from the grow - 220 pounds of stevi - This would translate into osideper acre with soil . Under cultivation , weeds grow much a sweeteningpower equiv - ing tips of branches rooted most quickly and faster than well - establishedstevia plants , and alent of approximately 28 tons per acre of grew into the largest plants . Plant dry weights weed control remains a problem . after 100 days reflect the difference in initial sucrose sugar . 2.9 grams for the vigor ( dry matter averaging Possible planting sites Experimental cultivation growing - tip cultures as opposed to 0.9 for Stevia apparently will produce best where plants derived from other cuttings ) , even Seeds and live plants were collected by the there is a long growing season , minimal frost , though these differences were minimized by author in the wild along tributaries of the high light intensities , and warmtemperatures . competition by other cuttings in the dense Ypane River in Paraguay . Seedswere planted The plant is not adapted to water stress or stand . in the greenhouseand in the field at the Uni - saline conditions . Stevia occurs naturally on In a greenhouse experiment to test relative versity of California , Davis , to monitor survi - acidsoilsof pH 4to 5 but willgrowwellon less productivity of 17 of the surviving clones of val . Germination occurred mostly on the acid to neutral soils with a pH of 6.5 to 7.5 . stevia , several clones were more productive sixthday and was very poor . About 200 stevia Although a wide range of sites for experi - of each than the others . Stevioside content plants were set out in the field in 1979to find mental plantings might be tried throughout clone has not been determined . those that would overwinter . Eighteen lines the state , southern coastal valleys away from A field clipping trial was planted in 1981 of 1979 - 80and survivedthe moderate winters the immediateinfluence of coastal fog would with plants of one clone , line 1 , to obtain data 1980 - 81 . Plant tops died back completely appear to be the most suitable . Any produc - as a function of plant on stevia productivity after light frosts except for line 18 , which re - tion should be attempted with caution appro - density and harvesting strategy . Plants were tained green branches . priate for a new crop with untested potential established at different densities and ferti - Sprouting began in March , but significant and problems . lized with nitrogen . growth did not occur until April . Slugs When plants were clipped just once , at the threatened survival of resprouting plants in Research needs the spring . Flowering occurred in October , end of the growing season , dry matter yield Steviais stilla plant of very recent domesti - but frost averaged or cold weather terminated the 920 grams per square meter . Plants cation . It is believed that yield improvements can be achieved by selectionand breeding for stevioside content , leaf - to - stem ratios , and plant response to fertilization . Other aspects needing investigation include methods of propagation , weed control , and water man - agement . Plants with high production of viable seed need to be found . Optimal ferti - lizer formulations for California need to be determined . Research in these areas might result in a new crop plant for California agri - culture . No seed is available for distribution at this time . A limited number of rooted cuttingsare For further details and a list of available . references , the article â?? Experimental Culti - vation of Rebaudiâ??s Stevia in California , â?쳌 Agronomy Progress Report 122 , is available from Department of Agronomy and Range ScienceExtension , 135 Hunt Hall , University of California , Davis , CA 95616 . ~ ~ Clinton C . Shock , former Research Assistant , Department of Agronomy and Range Science , University of California , Davis , is now Assistant In its natural surroundings in Paraguay , stevia grows to 24 inches tall . In trials at Davis , the Professor , Louisiana State University , Iberia Live - stock Experiment Station , Jeanerette . 28 tons per acre of sucrose sugar . plant produced sweetening power equivalent to CALIFORNIA AGRICULTURE , SEPTEMBER - OCTOBER1982 5