Regulatory mechanism of GA3 on tuber growth by DELLA-dependent pathway in yam (Dioscorea opposita).

KEY MESSAGE: Endogenous and exogenous GA3 responses to DoEXP and DoXTH depend on the DoGA20ox1, DoGA3ox1, DoGA2ox3, DoGA2ox4, DoGID1a, and DoDELLA1 to regulate yam tuber growth. Yam tuber undergoes significant alteration in morphogenesis and functions during growth, and gibberellins (GA) are considered potentially important regulators of tuber growth. However, it is little known about the regulation of GA metabolism and GA signaling components genes in tuber growth of yam. In this study, the cloning and expressions of GA3 level, GA metabolism and signaling genes, and cell wall genes in tuber growth in response to GA3 and GA biosynthesis inhibitor paclobutrazol (PP333) treatments were studied. The contents of GA3 accumulated at the tuber growth, with the highest levels in the early expansion stage. DoGA20ox1, DoGA3ox1, and four DoGA2ox genes were significantly abundant in the early expansion stage of tuber and gradually declined along with tuber growth. Three DoGID1 and three DoDELLA genes were showed different expression patterns in the early expansion stage of tuber and gradually declined along with tuber growth. Five DoEXP and three DoXTH genes expression levels were higher in the early expansion stage than in other stages. Exogenous GA3 increased endogenous GA3 levels, whereas the expression levels of DoGA20ox1, DoGA3ox1, DoGID1a, and DoDELLA1 were down-regulated in the early expansion stage of tuber by GA3 treatment, DoGA2ox3 and DoGA2ox4 were up-regulated. PP333 application exhibited opposite consequences. Thus, a mechanism of GA3 regulating yam tuber growth by DELLA-dependent pathway is established.

Genetic control of flowering in greater yam (Dioscorea alata L.).

BACKGROUND: Greater yam (Dioscorea alata L.) is a major tropical and subtropical staple crop cultivated for its starchy tubers. Breeding of this dioecious species is hampered by its erratic flowering, yet little is currently known on the genetic determinism of its sexual reproduction. RESULT: Here we used a genome-wide association approach and identified a major genetic barrier to reproduction in yam on chromosome 1, as represented by two candidate genes. A deleterious effect on male fitness could be hypothesized considering the involvement of these two genes in male reproduction and the low frequency of this non-flowering dominant allele within the male genepool. We also extended the hypothesis of a XX/XY sex-determination system located on chromosome 6 in D. alata to encompass most of the species diversity. Moreover, a kompetitive allele-specific PCR (KASPar) marker was designed and validated that enables accurate cultivar sex estimation. The reconstruction of chromosome 6 associated with the detection of highly putative structural variations confirmed the possible involvement of a major part of the chromosome. CONCLUSION: The findings of this study, combined with proper estimation of accession ploidy levels to avoid endosperm incompatibility issues, could facilitate the design of future promising parental combinations in D. alata breeding programs. Moreover, the discovery of this genetic barrier to reproduction opens new avenues for gaining insight into yam reproductive biology and diversification.

Cultivation and possible domestication of feral and possibly wild yams (Dioscorea spp.) in Southwest Ethiopia: ethnobotanical and morphological evidence.

The far Southwest Ethiopians transplant wild plant species to their gardens. One of such plant is the Dioscorea that we studied to assess the knowledge of wild yam and process of domestication. The study links two types of evidence to obtain insight about the process of yam domestication. We analyze two data sets derived from (1) ethnobotanical survey using 231 semi-structured interviews; and (2) morphological study in 47 yam accessions. Our study revealed that domestication is still active in some villages. Knowledge of yam domestication was shared by 44% of the farmers' even by those that have never practiced its domestication. Farmers who can describe the trend of domestication and the morphotypes of domesticate represented 21 and 28%, respectively. Farmers who have recent transplants in their garden varied from 4% in Bench to 10% in Sheko. The domestication process described by the two ethnic groups is similar. The duration of domestication can take up to six years, but with most of the individuals, it only takes three to five years. By linking the two types of evidence, two evolutionary processes are distinguished: (1) populations of recent domesticate expressing a domestication syndrome possibly belongs to the wild D. abyssinica or D. praehensilis, and (2) plants of incipient domesticate that might be derived from volunteers or diverse types of hybrids. Each of these processes can lead to integration of wild genotypes into the cultivated gene pool, and hence, enhance genetic diversity of cultivated yams. The domestication practices of traditional farmers should thus be taken into account if yam conservation and improvement plans need to be established.

Dioscorea Alata Tuber Proteome Analysis Uncovers Differentially Regulated Growth-associated Pathways of Tuber Development.

During its life cycle, the Dioscorea tuber undergoes multiple morphological and biochemical changes. To gain a better understanding of the metabolic changes associated with tuber growth, a stage-specific gel-free proteome analysis of four distinct morphological stages namely germinating tuber (S1), degrading tuber (S2), new tuber formation (S3) and tuber maturation (S4) was done and validated by principal component analysis. A comprehensive data set identifying 78.2% of the total 3,681 proteins was generated. PANTHER and KEGG MAPPER revealed both expected (carbohydrate metabolism and redox regulation) and novel biological processes (transcription factors and hormonal regulation) characteristic for each developmental stage. Higher abundance of the enzymes of ascorbate-glutathione cycle and carbohydrate metabolism was detected during tuber germination (S1) and tuber formation stages (S3) in comparison with the mature tuber. The presence of ethylene biosynthesis components during tuber formation hints toward its probable role in postharvest shelf life. The data set comprehensively describes the proteome of Dioscorea tuber and provides growth-specific markers for tuber germination (ascorbate peroxidase, monodehydroascorbate reductase, invertase) and tuber formation (sucrose synthase), which were validated by enzyme activity assays and Western blotting. The study provides information that may influence the direction of research for improving the productivity of this under-utilized and largely neglected crop.

A field trials-based authentication study of conventionally and organically grown Chinese yams using light stable isotopes and multi-elemental analysis combined with machine learning algorithms.

In this study, stable isotopes and multi-element signatures combined with chemometrics were used to distinguish conventional and organic Chinese yams based on field trials. Four light stable isotopes δD, δ13C, δ15N, δ18O, and 20 elements (e.g. Li, Na, Mn) were determined, then evaluated using significance analysis and correlation analysis, and modeling of various chemometrics methods. Consequently, the RandomForest model showed the best performance with AUC value of 0.972 and predictive accuracy of 97.3%, and Mn, Cr, Se, Na, δD, As, and δ15N were screened as significant variables. Moreover, many chemical components and antioxidant activity of yam samples were determined spectrophotometrically. The results indicated that organic yams had advantages in secondary metabolites such as polyphenol, flavonoid and saponin; conversely, conventional samples had more primary metabolites like protein and amino acids. Above all, this work provides a beneficial case in the authentication and quality evaluation of conventional and organic yams.

Organ- and Age-Specific Differences of Dioscorea polystachya Compounds Measured by UPLC-QTOF/MS.

Dioscorea polystachya, named Chinese yam, is widely cultivated as a functional food and natural medicine in China. There is currently little information about the chemical characteristics of Dioscorea polystachya in different organs (tuber cortex and tuber flesh) and at various ages. In this study, an ultra-high-performance liquid chromatography coupled to quadrupole time-of-flight mass spectrometry (UPLC-QTOF/MS) was used to profile chemical compounds in Dioscorea polystachya. As a result, thirty-eight compounds were detected in yam tuber cortex and tuber flesh. More compounds were detected in yam tuber cortex than in tuber flesh. Compounds such as dehydroepiandrosterone, allantoin and flavonoids were selected as biomarker candidates. Dehydroepiandrosterone was found more abundant in tuber flesh, while allantoin and flavonoids showed higher levels in tuber cortex. Furthermore, the levels of dioscin, malvalic acid and sucrose differed significantly among age groups and were highest in the tubers at 2 years. While the levels of allantoin, adenosine and glutamine increased with the growing years and were highest at 4 years. Thus, 2-year old Dioscorea polystachya tubers could be harvested to prepare dioscin, malvalic acid and sucrose supplements. The 4-year-old Dioscorea polystachya tubers would be the best choice for obtaining a large amount of allantoin and adenosine in industrial production.

Agro-ecological suitability assessment of Chinese Medicinal Yam under future climate change.

Chinese Medicinal Yam (CMY) has been prescribed as medicinal food for thousand years in China by Traditional Chinese Medicine (TCM) practitioners. Its medical benefits include nourishing the stomach and spleen to improve digestion, replenishing lung and kidney, etc., according to the TCM literature. As living standard rises and public health awareness improves in recent years, the potential medicinal benefits of CMY have attracted increasing attention in China. It has been found that the observed climate change in last several decades, together with the change in economic structure, has driven significant shift in the pattern of the traditional CMY planting areas. To identify suitable planting area for CMY in the near future is critical for ensuring the quality and supply quantity of CMY, guiding the layout of CMY industry, and safeguarding the sustainable development of CMY resources for public health. In this study, we first collect 30-year records of CMY varieties and their corresponding phenology and agro-meteorological observations. We then consolidate these data and use them to enrich and update the eco-physiological parameters of CMY in the agro-ecological zone (AEZ) model. The updated CMY varieties and AEZ model are validated using the historical planting area and production under observed climate conditions. After the successful validation, we use the updated AEZ model to simulate the potential yield of CMY and identify the suitable planting regions under future climate projections in China. This study shows that regions with high ecological similarity to the genuine and core producing areas of CMY mainly distribute in eastern Henan, southeastern Hebei, and western Shandong. The climate suitability of these areas will be improved due to global warming in the next 50 years, and therefore, they will continue to be the most suitable CMY planting regions.

Agromorphologic, genetic and methylation profiling of Dioscorea and Musa species multiplied under three micropropagation systems.

Plant in vitro vegetative propagation using classical semi-solid culture medium is limited due to the low degree of automation, suboptimal nutrient availability and induced physiological stress which often reduce its efficiency. Temporary Immersion System (TIS) emerged as an innovative approach to optimize and eliminate the drawbacks associated with the conventional system of micropropagation. In this study, both Dioscorea and Musa spp. were subjected to conventional semi-solid culture media, complete immersion in shaking liquid culture media and TIS using RITA bioreactor. In vitro grown plantlets were screened for possible vegetative changes using agro-morphological descriptors while genetic and methylation differences were assessed using amplified fragment length polymorphism (AFLP) and methylation-sensitive amplification polymorphism (MSAP). In vitro results showed that the number of shoots produced in Musa spp. varied significantly (P≤0.001) with the type of culture system. The highest mean shoot produced was observed with TIS (28.40) and the least using semi-solid culture medium (1.13). For Dioscorea spp., there was no significant interaction between the hormone combination and the culture system. However, the lowest mean shoot value (1.55) was observed in the semi-solid culture medium. Genetic analysis via AFLP using 15 primer pair combinations revealed that the 3 culture systems maintained genetic variation for Musa and Dioscorea spp. under in vitro and field conditions. Results showed 99% and 91% of the total bands were polymorphic under in vitro and field conditions respectively for Musa and 100% polymorphism for Dioscorea under in vitro and field conditions. Methylation investigation via MSAP using 12 primer pair combinations showed 25% and 46% polymorphic methylated-sensitive loci, 100% and 78% of non-methylated loci of the total bands generated under in vitro and field conditions respectively. Unmethylated (HPA+/MSP+) levels were highest in TIS (0.0842) as compared to CI (0.0227) and SS (0.0161) while full methylation or absence of target (HPA-/MSP-) was lowest in TIS (0.5890) and highest in SS (0.7138). For Dioscorea, 52% and 53% methylated sensitive loci and 100% non-methylated loci were polymorphic under in vitro and field conditions respectively. Although in vitro plant tissue culture techniques led to methylation at some loci of both species, there were no observable changes in the phenotype of both crops under field conditions. This also confirmed that not all methylation events lead to phenotypic changes.

Effects of yam/leguminous crops intercropping on soil chemical and biological properties of yam field.

We investigated the effects of yam/leguminous crops intercropping on soil chemical and biological properties as well as soil comprehensive fertility in a field experiment. Results showed that compared with the monoculture, both yam/alfalfa and yam/clover intercropping increased the concentrations of nitrate nitrogen (N), available phosphorus (P) and available potassium (K) in the 0-20 cm and 20-40 cm soil layers, while reduced soil pH and electrical conductivity (EC) in early growth period and rhizome rapid expansion period of yam. Intercropping with leguminous crops enhanced the activities of urease, alkaline phosphatase and catalase, and also enhanced soil basal respiration in the 0-20 cm and 20-40 cm soil layers during the whole growth period of yam. There was no influence of intercropping on soil sucrase activity and dehydrogenase activity. The effects of intercropping with leguminous crops on soil fertility at yam harvest were further analyzed by combining the membership function model and principal component analysis. Results showed that intercropping with leguminous crops could significantly increase the soil comprehensive fertility in the 0-20 cm and 20-40 cm soil layers. Therefore, it might be an effective measure to improve soil fertility and environmental quality, as well as alleviate continuous cropping obstacles of yam by yam/leguminous crops intercropping through enhancing soil biological diversity.

An integrated metabolomic strategy for the characterization of the effects of Chinese yam and its three active components on septic cardiomyopathy.

Chinese yam (CY), used as both a traditional Chinese medicine and a nutritious food, is an excellent candidate for treating septic cardiomyopathy (SCM). Adenosine, arbutin and allantoin are the major active components in the aqueous extract of CY. The aim of the present study was to interpret the roles of CY, adenosine, arbutin and allantoin in SCM treatment. Firstly, significant physiological indexes were examined to assess the model and treatment effects of CY, adenosine, arbutin and allantoin. Then, a metabolomic approach was utilized to reveal the metabolic disorders in SCM concerning the intervention of CY/adenosine/arbutin/allantoin. The integrated results demonstrated that adenosine, arbutin and allantoin are responsible for the efficacy of CY on SCM treatment by regulating amino acid, arachidonic acid, sphingolipid, glycerophospholipid and glycol metabolism. Moreover, adenosine and/or arbutin could be used as a substitute for CY in treating SCM, and allantoin efficacy was slightly weaker. This integrated metabolomic approach performed excellently in understanding the herbal function and the roles of its components.

Molecular basis of African yam domestication: analyses of selection point to root development, starch biosynthesis, and photosynthesis related genes.

BACKGROUND: After cereals, root and tuber crops are the main source of starch in the human diet. Starch biosynthesis was certainly a significant target for selection during the domestication of these crops. But domestication of these root and tubers crops is also associated with gigantism of storage organs and changes of habitat. RESULTS: We studied here, the molecular basis of domestication in African yam, Dioscorea rotundata. The genomic diversity in the cultivated species is roughly 30% less important than its wild relatives. Two percent of all the genes studied showed evidences of selection. Two genes associated with the earliest stages of starch biosynthesis and storage, the sucrose synthase 4 and the sucrose-phosphate synthase 1 showed evidence of selection. An adventitious root development gene, a SCARECROW-LIKE gene was also selected during yam domestication. Significant selection for genes associated with photosynthesis and phototropism were associated with wild to cultivated change of habitat. If the wild species grow as vines in the shade of their tree tutors, cultivated yam grows in full light in open fields. CONCLUSIONS: Major rewiring of aerial development and adaptation for efficient photosynthesis in full light characterized yam domestication.

[Regionalization study of Dioscorea nipponica in Jilin province based on MaxEnt and ArcGIS].

At the urgent practical issue of resource protection and artificial cultivation area selection of Dioscorea nipponica, the dominant environmental factors affecting the distribution of D. nipponicain Jilin province were selected by field investigation and using the maximum information entropy model and geographic information technology. MaxEnt model study found that the standard deviation of seasonal variation of temperature, precipitation in October and other six environmental factors on the growth of D. nipponica are the greatest impacting factors. The range of suitability for the growth of D. nipponica was 4.612 08×10-6-0.544 31, and the regionalization study was divided into four parts: high fitness area, middle fitness area, low fitness area and unfavorable area. The high fitness area is concentrated in the central and southern areas of Jilin Province, using ArcGIS statistical environment factors in the appropriate area of the numerical situation. The results showed that the regionalization study of D. nipponica was basically the same as the actual situation. It is clear that the natural environment suitable for the growth of D. nipponica is also the basis for the protection of the resources and the selection of cultivated area.

Asada-Halliwell pathway maintains redox status in Dioscorea alata tuber which helps in germination.

Reactive Oxygen Species (ROS) are important regulatory molecules governing physiological processes. In the present study a biochemical and proteome level comparison of two contrasting growth stages of Dioscorea alata tuber namely germinating and mature tuber was performed in order to understand the tuber physiology and biochemistry. Existence of all the component enzymes [APx (ascorbate peroxidase), GR (glutathione reductase), DHAR (dehydroascorbate reductase), MDHAR (mono-dehydroascorbate reductase)] and major products [ascorbate (ASC) and glutathione (GSH)] of the cycle showed an operational Asada-Halliwell cycle in the tuber. A 2.65 fold increase in ASC content & a 3.8 fold increase in GR activity fortified the redox milieu during germination. In contrast a 5 fold higher H2O2 content (due to 3.08 fold lower APx activity) and accumulation of reactive nitrogen species (RNS) such as nitric oxide (NO, 2.4-fold) and S-nitrosothiol (SNO, 2.08 fold) contributed to overall oxidative conditions in the mature tuber. The carbonic anhydrase (CA, 7.5 fold), DHAR (5.31 fold) and MDHAR (7 fold) activities were higher in the germinating tuber in comparison with the mature tuber. GSNO negatively regulated the CA (3.6 & 3.95 fold), MDHAR (7.5 & 1.5 fold) and APx (2.3 & 1.81 fold) while another NO donor, CysNO negatively regulated the DHAR (2.24 & 1.32 fold) activity in the mature and germinating stages respectively indicating again that the lesser inhibition by NO (via nitrosylation) may be because of overall reducing environment in the germinating tuber. Increased SNO leading to S-nitrosylation of dioscorin was confirmed by Biotin switch assay. This is the first report showing dioscorin nitrosylation. The present analysis showed differential redox regulation and also suggests the physiological relevance of CA, DHAR, MDHAR, APx & GR in tuber germination for the first time. These enzymes may be used as potential markers of tuber germination in future.

[New variety breeding of Dioscorea alata, cultivar "Wenshanyao No.1].

To breed a new yam cultivar of Dioscorea alata, the different and excellent germplasm resources were investigated within artificially cultivated population and some superior individuals, with a higher yield and medicinal properties, were selected. Considering results of the yield and medicinal properties during 2006-2013 cropping season, strains and lines were established and selected. As a result, the yield of the new developed cultivar (Wenshanyao No. 1, WSY01-1) reached 2217. 0 kg per 667 m2 (fresh weight) and 348.3 kg per 667 m2 (dry weight), and increased 23.8% and 23.9% comparing with control cultivars (landraces). Comparing with control cultivars, the level of polysaccharide, allantoin, and dioscin increased 36.9%, 48.3%, 20.9%, and reached 12.2%, 1.30%, 579.7 µg · g(-1), respectively. This result showed that the systematic selection method can significantly improve yield and medicinal properties of D. alata, and the developed " Wenshanyao No. 1" exhibits wide spreading prospects.

[Preparation Technique of Tetraploid of Dioscorea zingiberensis Synthetic Seed Based on Embryogenic Callus].

OBJECTIVE: To provide technical support for industrialization promotion of tetraploid of Dioscorea zingiberensis, the manufacturing method for synthetic seeds of tetraploid of Dioscorea zingiberensis was established and the correlated influential factors were studied. METHODS: By taking embryogenic calluses of tetraploid of Dioscorea zingiberensis as propagation materials, the influential factors such as components of artificial endosperm, seed coats,storage conditions and germination materials on germination and seedling of the synthetic seeds were evaluated. RESULTS: When 4% alginate +2% CaCl2 + 2% chitosan was served as seed coat materials, and 1/2 MS +0. 2 mg/L BA +0. 5 mg/L NAA + 0. 1 mg/L penicillin + 0. 3% carhendazim powder + 0. 2% sodium benzoate + 1. 0% sucrose + 0. 5% activated carbon + 1. 0% tapioca starch was served as endosperm, the synthetic seeds had high germination rate and seedling rate. After storing at 4 °C for 20 d, the germination rate and seedling rate of synthetic seeds was 76. 7% and 71. 7%, respectively. CONCLUSION: Manufacturing technology of synthetic seeds of tetraploid of Dioscorea zingiberensis with embryogenic calluses as propagation materials has production prospects.

Comparison of starches from five plants of Sect. Stenophora Uline and Sect. Lasiophyton Uline of Dioscorea grown in China.

BACKGROUND: Dioscorea resources with vital medicinal and functional values are abundant in south-west regions of China, especially in Sichuan Province. However, the resource in this region has received less attention compared with that of the north. D. zingiberensis, D. collettii, D. kamoonensis cv. Emei and Jinfo, and D. melanophyma from Sichuan Province and Chongqing City were studied with regard to the most abundant carbohydrate (starch) to search for new medicinal and food resources. RESULTS: The starches were small round granules or small oval granules and large elongated granules, except D. zingiberensis starch granules, which were disc-like in shape. D. zingiberensis and D. collettii starches showed higher values in total starch content, water-binding capacity and infrared ratio of absorbance bands at 1047/1035 and 1047/1022 cm⁻¹. Differential scanning calorimetry analysis demonstrated a higher gelatinisation temperature required more energy during the gelatinisation process. D. zingiberensis and D. collettii starches showed higher resistant starch content of 724.0 and 693.2 g kg⁻¹, respectively, with lower hydrolysis index and estimation of glycaemic index. All the starches exhibited an A-type pattern except D. melanophyma starch, which showed a C-type pattern evaluated by X-ray diffraction. CONCLUSION: These results showed that the starches with their low hydrolysis index values possessed potential values as healthy food.

[Research on Breeding of Dioscorea opposita cv. Tiegun].

OBJECTIVE: To breeding the new varieties Dioscorea opposita cv. Tiegun with the best comprehensive properties. METHODS: Seven new Dioscorea opposita. cv. Tiegun cultivars were screened by space mutation breeding of Dioscorea opposita cv. Tiegun bulbils. Yield,allantoin content,water soluble extractive and the resistance of these seven cultivars were compared with the main cultivar Dioscorea opposita cv. Tiegun( CK). Meanwhile, the nutrition quality of new cultivars No. 6 and No. 10 were compared with the main cultivar. RESULTS: (1) The fresh weight per plant ranked in the order as follows: No. 6 > No. 10 > No. 4 > No. 9 > No. 1 > CK > No. 2 > No. 8. The drying rate ranked in the order as follows: No. 2 > No. 10 > No. 9 > No. 6 > No. 8 > CK > No. 1 > No. 4. Dry weight per plant ranked in the order as follows: No. 10 > No. 9 > No. 6 > No. 2 > No. 1 > CK > No. 4 > No. 8. The fresh weight per plant, drying rate and dry weight per plant of No. 6 and No. 10 were higher than the main cultivar. (2) The allantoin content ranked in the order as follows: No. 6 > No. 4 > No. 10 > CK > No. 9 > No. 8 > No. 2 > No. 1. (3) The water soluble extractive contents ranked in the order as follows: No. 6 > No. 2 > No. 4 > No. 10 > No. 1 > CK > No. 9 > No. 8. The water soluble extractive content of No. 6 was higher than No. 10 and the main cultivar. (4) No. 10 had the best taste of dry, soft, sweet and fragrant, No. 6 had the taste of dry, floury and hard, and No. 9 had the taste of dry and crisp. (5) No. 6 had the strongest resistance to Gloeosporium pestis and Cykindrosporium dioscoreae; No. 10 had a middle resistance to Gloeosporium pestis and a strong resistance to Cykindrosporium dioscoreae; and the main cultivar had a middle degree of being prone to Gloeosporium pestis and a middle resistance to Cykindrosporium dioscoreae. (6) The content of starch, reducing sugar, protein and ash in No. 6 and No. 10 were higher than that of the main cultivar,while the content of water in No. 6 and No. 10 were lower,which indicated that the nutrition quality of No. 6 and No. 10 is better than the main cultivar. CONCLUSION: The new cultivar No. 10 is suitable for popularizing as a new variety of edible Dioscorea opposita cv. Tiegun. The new cultivar No. 6 is suitable for popularizing as a new variety of medicinal Dioscorea opposita cv. Tiegun.

[Study on Rapid Micropropagation in Vitro Technique of Guangfeng Medicinal Yam (Dioscorea opposita) Plantlets].

OBJECTIVE: In order to provide methodology reference for virus-free and germplasm conservation of Guangfeng medicinal yam (Dioscorea opposita) plantlets, rapid micropropagation in vitro technique of Guangfeng medicinal yam plantlets was studied. METHODS: Using the method of plant tissue culture, single factor test and flow-cytometry, the basic procedure of Guangfeng medicinal yam tissue culture was established and the DNA content of Guangfeng medicinal yam plantlets and its potted seedlings was detected. RESULTS: The best disinfection procedure of stems with a bud of Guangfeng medicinal yam was washed with sterile water for three times after sterilized with 70% alcohol for 20 - 30 s and then washed with sterile water for three times again after sterilized with 0.1% mercuric chloride for 10 - 12 min; The best explants of stems with a bud of Guangfeng medicinal yam was slightly woody and more mature stems witha bud; The best proliferation culture medium of stems with a bud of Guangfeng medicinal yam was MS + 6-BA 2.0 mg/L + NAA 0.1 mg/L; The best rooting culture medium of stems with a bud of Guangfeng medicinal yam was MS + NAA 0.5 mg/L; The best culture method of Guangfeng medicinal yam plantlets was liquid culture; The best transplanting matrix of Guangfeng medicinal yam plantlets was the mixture of paddy clay and fine sand (1: 2) or the mixture of perlite and vermiculite (1: 2); The DNA content between Guangfeng medicinal yam plantlets and its potted seedlings had no significant difference. CONCLUSION: A fast and efficient micropropagation in vitro technological system of stems with a bud of Guangfeng medicinal yam is established, and the flow cytometry detect results also show the genetic stability of Guangfeng medicinal yam plantlets, whose results provide the technical and theoretical basis for the large-scale production of Guangfeng medicinal yam plantlets.

[Studies on genetic relationship of Dioscorea].

Based on the results of the morphologic studies on genus Dioscorea, the paper summarized the entire chemical constituent that isolated from this genus and analyzed it with the methods of chemotaxonomy. The rules of the chemical constituent and pharmacodynamic effects were analyzed. Seventeen species which belong to Sect. Stenophora Uline of Dioscorea contain steroidal sapogenin. Other species with different main components such as polysaccharide and tannin have have different effects. This chemotaxonomic view point will conduce to establish a phylogeny of the genus Dioscorea.

[Preliminary study of Dioscorea bulbifera plantlet microtuber in vitro induction].

OBJECTIVE: In order to provide a theoretical basis for the microtuber factory production and its germplasm resources preservation, in vitro induction of Dioscorea bulbifera plantlet microtubers was studied. METHODS: Through plant tissue culture technique and single factor experiment method, stems with buds of Dioscorea bulbifera plantlets as explants, the effects of various factors such as sugar, inorganic salt, cultivation mode, activated carbon and physiological state of stems with buds on in vitro induction of Dioscorea bulbifera microtubers were studied. RESULTS: The optimal sugar of Dioscorea bulbifera microtuber in vitro induction was 60 g/L sucrose or 90 g/L white sugar. The best inorganic salt concentration of Dioscorea bulbifera microtuber in vitro induction was MS. The best culture method of Dioscorea bulbifera microtuber in vitro induction was solid-liquid double layer culture. Activated carbon had a significant effect on Dioscorea bulbifera microtuber in vitro induction, whose optimum concentration was 0.03%. More mature the stem with buds was, the shorter the time of microtuber formation need. CONCLUSION: This experiment establishes a rapid method of Dioscorea bulbifera microtuber in vitro induction for the first time,which provides a new way for the application of Dioscorea bulbifera microtubers in agricultural production.