The Effects Of GA And CCC On Main Agronomic Traits, Physiological Indexes And Steviol Glycosides Yields Of 4 Different Stevia Rebaudiana Lines

Stevia rebaudiana Bertoni belongs to the Stevia genus and Asteraceae family. It is named Sweet-leaf Chrysanthemum in Chinese because of the whole plant, especially in leaves, riching in glycosides, alias Sweet Chrysanthemum, Sweet weed or Sweet Tea et.al. S. rebaudiana is native to semitropical region of South America, which introduced into China successfully in 1977 and had planted in more than 20 provinces and cities of the whole country now. Recently in Sichuan province, the agricultural planting area of S. rebaudiana is larger and larger as days going on. The dry leaves and stems of S. rebaudiana are sweet and of fresh smelling, which can be used as natural botanic medicine, or be used to extract glycosides as sweeten additives. The glycosides in S. rebaudiana are of high sugariness and low calorie trait, so it is hornored as the third sweeten-plant in the world ranked after sugarcane and beet. Plant growth regulators GA and CCC are widely used to improve plants yield and quality. Steviol glycosides, the main effective compositions of S. rebaudiana share the same biosynthetic way with GA before ent-kanrene formed. However, CCC plays antagonistically with GA, which impeds geranylgeranyl diphosphate (GGPP) transferring into ent-kanrene to hinder GA forming. In this study, we had selected excellent single plants and discussed the different types of S. rebaudiana planting in Sichuan province, and we finally selected out 4 representative lines; we further studied the effects of GA and CCC on main agronomic traits, physiological indexes, endohormones and steviol glycosides yields of the 4 different lines, in order to provide some references for better cultivation of S. rebaudiana. The main results of these studies are as follow:1. There were significant differences in RA and ST contents among 46 plants, among which RA content ranged from 0 to 10.56%, ST content ranged from 2.90% to 20.97%, RA+ST content ranged from 4.72% to 21.74%, RA/(ST+RA) ranged from 0 to 0.758, ST/(ST+RA)ranged from 0.242 to 1.000 and RA/ST ranged from 0 to 3.139. The classification based on cluster analysis of steviol glycosides contents was different from that based on the phenotype of the plants, which indicated that there might be no significant correlation between the traits of phenotypes and RA or ST content in S. rebaudiana. It could be necessary to detect the glycosides contents in single plant of S. rebaudiana during the breeding.2. In the 4 different types of S. rebaudiana lines, SRI was high ST content line, SR2 was high RA content line, SR3 was high RC content line and SR5 was high ST and low RA content line. RA content in 4 lines was SR2>SR3>SR1>SR5 in order, and the highest content line was SR2, in which the RA content was 11.59±0.43%; the second highest content line was SR3, in which the RA content was 8.70±0.12%. ST content in 4 lines was SR5>SR1>SR2>SR3 in order, and the higher content lines were SR5 and SR1, in which the ST content were 17.39±0.40% and 15.26±0.26% repectively. The RA+ST content in 4 lines from high to low was SR1>SR2>SR5>SR3, and SR3 which was rich in RC content, was the lowest RA+ST content line among the 4 lines. RA/ST ration of SR3 was close to SR2, however, RA and ST contents in SR2 were significantly higher than that in SR3.3. Compared with contrast, plant height and node length increased significantly, leaves length became longer and leaves width became narrower, and leaves length/width ratio increased, after S. rebaudiana lines were sprayed with GA. Plant height was higher and higher as the concentration of GA increased, while leaves length and leaves width decreased. Except SR2, dry leaves yields of the other lines decreased significantly after GA treated.After S. rebaudiana lines were sprayed with CCC, the color of plants' leaves were darker, and the leaves became thicker, there was a tendency of decreasing in plant height and node length as concentration of CCC increased, however, CCC treatment finally made no significant difference with contrast. Treated with 100 mg/L and 500 mg/L CCC improved the dry leaves yields of SR1, and 300 mg/L CCC improved the dry leaves yield of SR2.4. The activities of POD, CAT, SOD and contents of MDA in S. rebaudiana lines were generally improved, especially at higher concentration of GA, which might bring oxidative stress to S. rebaudiana. However the activities of POD, CAT, SOD and contents of MDA in 4 S. rebaudiana lines were decreased when applied with CCC, which indicated CCC might be benifint to S. rebaudiana. After sprayed with GA, the soluble sugar contents of 4 different lines increased, while which slightly declined or kept the same lever with contrast when treated with different concentrations of CCC. The changes of soluble sugar contents were approximately opposite to that of total glycosides.5. GA and CCC treatments made endohormones ZT contents increased(except SR2), while IAA contents declined(except SR5). Treated by CCC, ZT/IAA ratio improved significantly in SR1 and SR3, however which declined in SR5 and kept the same in SR2. The changes of ZT/IAA ratio treated by GA were similar as CCC treatments. It is generally considered that higher ZT/IAA ratio helps the growth of shoots, but the dry leaves yields of SR1 and SR3 did not improve as the ZT/IAA ratio improved after spayed exohormone. And there seemed to be no relationship between glycosides contents and endogenous ZT, IAA or their ratio.6. For high ST content type line SRI, sprayed CCC or 100 mg/L GA were benefit to improve RA content and RA/ST ratio, and lower ST content at the same time; The better treatments were 100 mg/L GA (A1) and 500 mg/L CCC (C3), which improved RA content to 7.29% and 8.26% respectively, and improved RA/ST ratio from 0.4331 of contrast to 0.7678 and 0.6457 respectively. For high ST and low RA content type line SR5, sprayed 100 mg/L or 300 mg/L CCC helped SR5 to accumulate more ST and surpress RA, and improve ST/RA ratio, which meant conveniently extracting and purifying during productive processes. For high RA content type lines SR2 and SR3, different concentrations of GA or CCC treatments did not benifit to improve RA content or RA/ST ratio.7. The yields of RA, ST, RA+ST of SRI improved largely as 100 mg/L CCC treated, but considering improving RA content as well as RA/ST ratio,500 mg/L CCC was optimal to improve the sweetener-used quality of SRI.100 mg/L or 300 mg/L CCC could improve ST yield and ST/RA ratio of SR5 line, which was abundant in ST and rare in RA. To improve the medicine-used quality, spraying 100 mg/L CCC is better than 300 mg/L CCC. Different concentrations of GA or CCC treatments did not help to improve RA yields or RA/ST ratio of high RA content type lines SR2 and SR3.Summing up, the effects of GA or CCC on main agronomic traits, physiological indexes and steviol glycosides contents and yields of 4 different type Stevia rebaudiana lines were different. GA treatments were not good for improving dry leaves yield and steviol glycosides contents. The plant height became higher and leaves became narrower, endogenous ZT contents increased and IAA declined by spraying with GA, and S. rebaudiana might suffer oxidative stress at higher concentration of GA. CCC treatments made the plants grow healthier and the leaves greener, endogenous ZT and IAA contents increased. Appropriate concentrations of CCC could relieve oxidative stress, improve dry leaves yield and glycosides contents, however, the idiographic concentration was different for different lines.