Raghavan Ramakrishnan Nair

High-frequency plant regeneration through cyclic secondary somatic embryogenesis in black pepper (Piper nigrum L.)

A high-frequency plantlet regeneration protocol was developed for black pepper (Piper nigrum L.) through cyclic secondary somatic embryogenesis. Secondary embryos formed from the radicular end of the primary somatic embryos which were originally derived from micropylar tissues of germinating seeds on growth regulator-free SH medium in the absence of light. The process of secondary embryogenesis continued in a cyclic manner from the root pole of newly formed embryos resulting in clumps of somatic embryos. Strength of the medium and sucrose concentration influenced the process of secondary embryogenesis and fresh weight of somatic embryo clumps. Full-strength SH medium supplemented with 1.5% sucrose produced significantly higher fresh weight and numbers of secondary somatic embryos while 3.0 and 4.5% sucrose in the medium favored further development of proliferated embryos into plantlets. Ontogeny of secondary embryos was established by histological analysis. Secondary embryogenic potential was influenced by the developmental stage of the explanted somatic embryo and stages up to “torpedo” were more suitable. A single-flask system was standardized for proliferation, maturation, germination and conversion of secondary somatic embryos in suspension cultures. The system of cyclic secondary somatic embryogenesis in black pepper described here represents a permanent source of embryogenic material that can be used for genetic manipulations of this crop species.

Somatic embryogenesis and plant regeneration in black pepper (Piper nigrum L.): I. Direct somatic embryogenesis from tissues of germinating seeds and ontogeny of somatic embryos

Summary A protocol was developed for induction, maturation and germination of somatic embryos from the tissues of germinating seeds of black pepper (Piper nigrum L.). Explants were cultured on growth regulator – free solid SH medium maintained in the dark. The first somatic embryos developing directly from the explant tissue were noticed after 60 d of culture. Somatic embryos originated from a ring-like tissue on the micropylar region of the seeds. Sucrose concentration of the medium was found to be crucial for the induction of somatic embryos, and 30 g l–1 was found to be the optimum. Maturation and germination of somatic embryos were achieved on the same medium. Suspension culture enhanced the process of maturation and germination. Regenerated plants were established in soil. Histology confirmed the ontogeny and each stage of development. Growth regulators were found to inhibit the induction of somatic embryogenesis. Cytological analysis of the regenerated plants revealed the normal chromosome number of 2n=52.SummaryA protocol was developed for induction, maturation and germination of somatic embryos from the tissues of germinating seeds of black pepper (Piper nigrum L.). Explants were cultured on growt...

Somatic association of chromosomes and other mitotic abnormalities in Vanilla planifolia (Andrews)

SUMMARYAbnormal mitotic behaviour in Vanilla planifolia is analysed with special emphasis to association of somatic chromosomes. Indications of somatic association were evident in interphase, prophase and metaphase stages of root tip mitosis. Reasons for somatic association is discussed. Possible origin of vanilla as a hybrid is suggested. Role of somatic association in enriching variability is also discussed.

Variation in pollen fertility and chromosome number among germplasm collections of ginger (Zingiber officinale Rosc.)

AbstractPollen fertility in 21 germplasm collections of ginger was determined by glycero-carmine staining and in vitro germination. Pollen fertility based on staining ranged from 5.59% to 67.73%, while in vitro germination ranged from 2.35% to 60.31% in different collections analyzed. High pollen stainability was not always followed by high in vitro germination in collections analyzed. However, the in vitro germination percentage was always lower than the percentage of stainability in all the collections. Highest in vitro pollen germination was recorded in acc. no. 195 (60.31%) followed by acc. no. 821 (50.67%). Somatic chromosome number analysis of the collections revealed that the two collections with high pollen fertility (acc. nos. 195 and 821) were tetraploids with 2n = 44 while most of the other collections had 2n = 22, the normal chromosome number. One collection with aneuploid chromosome number of 2n = 24 had lower pollen germination (4.82%), similar to many diploid collections. Tetraploids are id...Abstract Pollen fertility in 21 germplasm collections of ginger was determined by glycero-carmine staining and in vitro germination. Pollen fertility based on staining ranged from 5.59% to 67.73%, while in vitro germination ranged from 2.35% to 60.31% in different collections analyzed. High pollen stainability was not always followed by high in vitro germination in collections analyzed. However, the in vitro germination percentage was always lower than the percentage of stainability in all the collections. Highest in vitro pollen germination was recorded in acc. no. 195 (60.31%) followed by acc. no. 821 (50.67%). Somatic chromosome number analysis of the collections revealed that the two collections with high pollen fertility (acc. nos. 195 and 821) were tetraploids with 2n = 44 while most of the other collections had 2n = 22, the normal chromosome number. One collection with aneuploid chromosome number of 2n = 24 had lower pollen germination (4.82%), similar to many diploid collections. Tetraploids are identified for the first time from germplasm collections of ginger. The role of polyploidy in improving pollen fertility in ginger is discussed.