RAPD analysis of somaclonal variants derived from embryo callus cultures of peach

An assessment for in vitro propagation and genetic stability of Phoebe goalparensis Hutchinson, an endemic valuable timber tree of North East India

BACKGROUND

Phoebe goalparensis is an endemic forest species of North East India that belongs to Lauraceae family. P. goalparensis is used as timbers yielding plants for commercial importance in the local furniture markets of North East India. A rapid in vitro micropropagation protocol was established by using apical and axillary shoot tips on Murashige and Skoog medium with varied concentrations of plant growth regulators.

RESULTS

In this study, 5.0 mg/l BAP augmented medium was chosen as the best for shoot multiplication of the plant. However, IBA (2.0 mg/l) was the most responsive for root induction. Moreover, 70% of root induction was recorded during rooting experiment and 80-85% survivability was observed during the acclimatization of this species. Clonal fidelity of P. goalparensis was determined with ISSR marker and it was observed that in vitro raised plantlets were polymonomorphic.

CONCLUSION

Hence, an efficient protocol with high proliferation and rooting was established for P. Goalparensis that could aid in massive propagation in future.

Micropropagation and Biomass Production of True-to-Type Stevia rebaudiana Bertoni

Here we describe an efficient micropropagation protocol for Stevia rebaudiana Bertoni. We present experiments carried out to optimize the suitable media for in vitro shoot multiplication and root induction and to study the effect of culture vessel on shoot multiplication. Among all different media tested for in vitro shoot multiplication, hormone-free liquid medium is most suitable. The highest number of nodes per shoot (5.4) and length of shoot (4.76 cm) at 4 weeks after subculturing are observed when single node explants are placed on modified MS medium supplemented with 1 % sucrose and 0.7 % agar. The highest response of multiplication rate (9.56) is observed on half strength of macroelement of MS with full strength of microelement of MS and 170 mg/l KH2PO4, and 185 mg/l MgSO4 in plastic growth container. Further, RAPD marker analysis of in vitro-raised plants maintained their clonal fidelity and true-to-type without showing any somaclonal variation.

In vitro plant propagation of Catharanthus roseus and assessment of genetic fidelity of micropropagated plants by RAPD marker assay

An investigation was carried out to develop an efficient micropropagation protocol for Catharanthus roseus. Experiments were conducted to optimize suitable media for in vitro shoot multiplication and root induction. Out of the different media compared for in vitro shoot multiplication, Murashige and Skoog (MS) medium supplemented with 1 mg/l of 6-benzylaminopurine and 0.2 mg/l α-naphthaleneacetic acid showed better response in terms of the emergence of shoots from axillary buds as well as proliferation and multiplication of shoots. The shoots when placed on half strength of MS medium having 1 mg/l indole 3-butyric acid and 0.25 % charcoal showed cent percent root induction with maximum number of roots per shoot (4.2) as well as maximum root length (1.72 cm). Further, clonal fidelity of the in vitro-raised plants was carried out using randomly amplified polymorphic DNA marker and results indicated that all the tissue culture-derived plants are true-to-type and there were no somaclonal variations among these plants.

Micropropagation of seedless lemon (Citrus limon L. cv. Kaghzi Kalan) and assessment of genetic fidelity of micropropagated plants using RAPD markers

A micropropagation protocol was developed for multiplication of seedless lemon (Citrus limon L. cv. Kaghzi Kalan) using nodal explants. The maximum shoot regeneration was observed on low level of BAP (0.1 mg l(-1)) or kinetin (0.5 mg l(-1)). BA was recorded to be better than kinetin in terms of number of days taken to bud break. The maximum number of shoots per explant was observed on 0.1 mg l(-1) BA and 0.5 mg l(-1) kinetin. Shoot proliferation decreased with increasing concentration of BA alone, but in case of a combination of BA and NAA (0.1 mg l(-1) each), it increased with increasing concentration of BA up to 10.0 mg l(-1). None of the treatments including BA or kinetin alone or BA in combination with NAA produced significantly more shoots for commercial exploitation. In the case of a combination of BA + kinetin + IBA, the maximum (5.5 shoots per explants) proliferation was observed on MS medium containing 1.0 mg l(-1) BA + 0.5 mg l(-1) kinetin + 0.5 mg l(-1) IBA or 0.25 mg l(-1) BA + 1.0 mg l(-1) kinetin + 1.0 mg l(-1) IBA. Regenerated shoots showed root induction on MS basal medium or on MS medium containing 1.0 mg l(-1) IBA. It is concluded that a five-fold increase (1.0 mg l(-1) BA + 0.5 mg l(-1) kinetin + 0.5 mg l(-1) IBA) in axillary shoot proliferation, while seven-fold increase (0.25 mg/l mg l(-1) BA + 1.0 mg l(-1) kinetin + 1.0 mg l(-1) IBA) during the second cycle of multiplication could be obtained using the two plant growth regulator combinations. PCR amplification with 14 different random primers confirmed no somaclonal variant up to two cycles of shoot multiplication.

Genetic instability in calamondin (Citrus madurensis Lour.) plants derived from somatic embryogenesis induced by diphenylurea derivatives

Somatic embryos were regenerated in vitro from calamondin style-stigma explants cultured in the presence of N (6)-benzylaminopurine (BAP) cytokinin and three synthetic phenylurea derivatives, N-(2-chloro-4-pyridyl)-N-phenylurea (4-CPPU), N-phenyl-N'-benzothiazol-6-ylurea (PBU) and N,N'-bis-(2,3-methilendioxyphenyl)urea (2,3-MDPU). The phenylurea derivative compounds tested at micromolar level (12 muM) were able to induce a percentage of responsive explants significantly higher from that obtained with BAP and hormone-free (HF) conditions. In order to verify the genetic stability of the regenerants, 27 plants coming from different embryogenic events were randomly selected from each different culture condition and evaluated for somaclonal variations using inter-simple sequence repeat and random amplified polymorphic DNA analyses. We observed that 2,3-MDPU and PBU gave 3.7% of somaclonal mutants, whereas 4-CPPU gave 7.4% of mutants. No somaclonal variability was observed when plantlets were regenerated in BAP or HF medium. Although diphenylurea derivatives show a higher embryogenic potential as compared to BAP, they induce higher levels of somaclonal variability. This finding should be taken in consideration when new protocols for clonal propagation are being developed.

Plant regeneration through somatic embryogenesis from tissues of mature oak trees: true-to-type conformity of plantlets by RAPD analysis

Somatic embryogenesis was induced in expanding leaf explants excised from epicormic shoots forced from branch segments taken at four different times of year from a mature oak (Quercus robur L.). Branch segments 2-4 cm in diameter produced most shoots when collected in March. Somatic embryos were induced on explants derived from branches of all collection dates, although collection in November seemed to afford the best results. Germination and conversion ability of embryos of embryogenic lines derived from six oak trees depended heavily on genotype, conversion rates ranging from 0 to 70%. RAPD analyses found no evidence of genetic variation either within or between the embryogenic lines established from three of these trees, or between these lines and the trees of origin, or between somatic embryo derived plantlets and the trees of origin. The embryogenic system used in this study appears to be suitable for true-to-type clonal propagation of mature oak genotypes.

Detection of microsatellite instability during somatic embryogenesis of oak (Quercus robur L.)

Five microsatellite loci (QpZAG1/5, QpZAG9, QpZAG36, MSQ4, MSQ13) were used to test for genetic stability of three somatic embryogenic culture lines of Quercus robur L. and plantlets derived therefrom. DNA variation was detected among somatic embryos within all embryogenic lines, whereas no genetic instability was found among the regenerated plants. Two microsatellite loci revealed variation, and a locus-dependent instability was observed. The most polymorphic and useful microsatellite locus for detecting genetic variation was QpZAG9, with 28.5% of the investigated loci being variable.

Genetic stability of micropropagated almond plantlets, as assessed by RAPD and ISSR markers

Almond shoots produced by axillary branching from clone VII derived from a seedling of cultivar Boa Casta were evaluated for somaclonal variation using randomly amplified polymorphic DNA (RAPD) and inter-simple sequence repeats (ISSR) analysis. To verify genetic stability we compared RAPD and ISSR patterns of plantlets obtained after 4 and 6 years of in vitro multiplication. A total of 64 RAPD and 10 ISSR primers gave 326 distinct and reproducible band classes, monomorphic across all 22 plantlets analysed. Thus, a total of 7,172 bands were generated, exhibiting homogeneous RAPD and ISSR patterns for the plantlets tested. These results suggest that the culture conditions used for axillary branching proliferation are appropriate for clonal propagation of almond clone VII, as they do not seem to interfere with the integrity of the regenerated plantlets. These results allowed us to establish the use of axillary branching plantlets (mother-plants) as internal controls for the analysis of somaclonal variation of shoots regenerated from other in vitro culture processes performed with clone VII (adventitious regeneration, regeneration from meristem culture, virus sanitation programs and genetic engineering).

Maturation and germination of oak somatic embryos originated from leaf and stem explants: RAPD markers for genetic analysis of regenerants

Experiments were performed to determine the influence of maturation medium carbohydrate content on the rates of germination and plantlet conversion (root and shoot growth) of somatic embryos from four embryogenic lines derived from leaf or internode explants of Quercus robur L. seedlings. The conversion rate was favoured by high carbohydrate content as long as the maturation medium contained at least 2% sucrose, which was necessary for healthy embryo development. Given this, sorbitol and mannitol favoured the conversion rate more efficiently than sucrose, the highest rate, 32%, being achieved by medium with 6% sorbitol and 3% sucrose. Maturation treatment did not affect the root or shoot lengths of converted embryos. In supplementary experiments, 2 weeks of gibberellic acid treatment between maturation and germination treatments did not improve germination rates, but did reduce root length and the number of leaves per regenerated plantlet. In the four embryogenic lines tested, plant recovery rate was enhanced by inclusion of benzyladenine into the germination medium following culture of the embryos on maturation medium with 6% sorbitol and 2-3% sucrose. In embryogenic systems it is important to assess the uniformity of the regenerants. Random amplified polymorphic DNA (RAPD) analysis using 32 arbitrary oligonucleotide primers was performed to study variability in DNA sequences within and between four embryogenic lines. No intraclonal nor interclonal polymorphism was detected between embryogenic lines originating from different types of explant from the same seedling, but every one of the primers detected enough polymorphism among clones originating from different plants to allow these three origins to be distinguished. No differences in DNA sequences between regenerated plantlets and their somatic embryos of origin were detected, but a nodular callus line that had lost its embryogenic capacity was found to be mutant with respect to three other clones originating from the same plantlet. This study shows that high carbohydrate levels in the maturation medium significantly increase plant conversion of oak somatic embryos, which exhibit no variation in DNA sequences when proliferated by secondary embryogenesis.

Intra-clonal variation and a similarity threshold for identification of clones: application to Salix exigua using AFLP molecular markers

Although molecular methods are a major advance over phenological or root connectivity studies in the identification of clonal plants, there is still a level of ambiguity associated with two types of error: misidentification of genetically similar seedlings as clones and misidentification of dissimilar fingerprints from clones as genetically distinct individuals. We have addressed the second of these error types by determining the level of variation for AFLP fingerprints in Salix exigua, and then by developing a threshold value of Jaccard's similarity index for assigning individuals to clones or to siblings. Variation in AFLP banding patterns among clones was partitioned into three potential sources; clones, stems within-clones and foliage within-stems. Most of the variation was attributable to clones and then to stems within-clones. To provide an objective means of identifying clones, we developed a method for establishing a threshold similarity index to assign individuals to the same clone. Our method yielded a Jaccard similarity threshold of 0.983 that resulted in a potential pairwise error rate of 8.1% putative clone assigned to siblings and 1.5% sibling assigned to clones. The method was tested on independent clonal and sibling individuals resulting in the same threshold value and similar error rates. We applied our method to assign individuals to clones in a population of S. exigua along the Cosumnes River, California. A total of 11 clones were identified, with one clone including 43% of the individuals sampled. Our results show that this approach can be useful in the accurate identification of clones.