Study On Rooting And Acclimatization Of Tissue Culture Rhubarb Plants And Field Growth Characters

Culinary rhubarb (Rheum rhaponticumL.) is a species belonging to the family Rheum of Polygonaceae. Its long, thick and juicy petiole has unique taste and is used as vegetable. Rhubarb petiole is rich in pro-vitamin A and vitamin C, succinic acid, calcium, phosphorous, and high dietary fiber. Therefore, rhubarb becomes favorite health-care food. China is one of the original areas of culinary rhubarb, but its cultivation for vegetable is little known. Introduction and cultivation of culinary rhubarb are important to enrich germplasm resources abd increase variety of health-care vegetable species. In order to speed up the process of introduction, cultivation and breeding of culinary rhubarb plant tissue culture has been applied for rapid propagation of rhubarb planting materials.Our laboratory has involved in introduction of rhubarb cultivars since 2004. It has successfully established the in vitro regeneration system of 6 rhubarb varieties by using shoot-tip culture method. Previous study has set up the groundwork for extension and cultivation of rhubarb. Rooting, acclimatization and plantlet transplanting are major factors for improve survival rate of tissue cultured plants. So far, in vitro rooting, acclimatization of micropropagated rhubarb plants has not been well studied. This thesis reports the characteristics of in vitro rooting, acclimatization and transplanting of regeneratged plants by investigatng 4 rhubarb cultivars (Rt,Ro,R19,R17).This thesis has achieved the following results and technical information:(1) Characteristics of in vitro rooting from 4 cultivars of culinary rhubarb were investigated. It was observed that the rate of callus formation from regerated plantlets could reach to 100% after 10d, with the rate of root formation reaching to 100% after 14d. Cultivars Rt,R19,R17 produced showed the callus formation of 100% in 8d. Cultivar Rt showed the most rapid rooting ability, reaching to 100% in 12d. According to the data of callus and rooting, a"Logistic"model, with"S"stype, of 4 rhubarb cultivars was created for predicating the progress of callus formation and in vitro rooting for micropropagated plantlets. According to the model, three in vitro rooting stages can be noted, including root number increasing stage (7-14d), root enlongation stage(14d-21d)and root aging stage (after 21d).(2) According to the result, rooting temperature and different fixtures had direct influence on survival rate of transplantion during acclimatization. At 20±2℃the highest survival rate (90%) of transplantation was obtained from regenerated plantlets with 14d rooting in agar media, followed by 7 days acclimatization. At 27-32℃, the highest survival rate (79.2%) of transplanting was obtained for plants rooted in river sand or vermiculite for 21d, followed by 7d acclimatization, however, under the same condition the survival rate was 25.9% for plants rooted in agar media.(3) The sucrose concentrations (from 0 to 40g/L) showed substantial effects on survival rate of transplantation, with sucrose concentration at 30g/L achiving the highest survival rate (88.9%). Different organic additives also had prominent influence on acclimation and transplant survival rate of regenerated plants. The treatments with coconut juice 30g/L and banana 10g/L respectively obtained survival rate 100%, while treatments added with soymilk 3g/L and 5g/L had the lowest transplant survival rate of 93.3%. All the results are significantly different from 88.9% for plants rooted in 30g/L sucrose media.(4) The results demonstrate that hardening off at 20℃can achieve relatively high transplant survival rate, and different time of hardening off had a significant effects on leaf stomata characters of regenerated plantlet. At the first 7 days of hardening off, there was significant variation in stomata width, length and closure rate, 7 days later, these three indexes had no significant change. There was very little difference in stomatal closure rate between plants with 7 days'hardening off and micropropagated plants growing 3 months in the field, indicating that 7 days of hardening off is a appropriate period for acclimatization.(5) Field trials indicated that culinary rhubarb has a relatively stronger cold-resistance, and it can successfully over-winter at -12℃. It starts growth at the beginning of March, flower blossoms at mid-May, and seeds mature in early July. It becomes dormancy in November. It can be harvested in June and September. Field observation showed great differences in morphological characters among different cultivars and these morphological characteristics can be used as basical standard of cultivar selection. In addition, analysis in mineral elements reveals difference in mineral content between cultivars, R5 had a higher content of calcium, and RV has a higher content of iron and zinc, while RO had a higher content of manganese. It also noted that culinary rhubarb are prone to diseases of pythium debaryanum in seeding stage and root rot in rainy summer. Grub and prodenia litura are the main pests to be controlled.