Y. P. S. Bajaj

Regeneration of plants from potato meristems freeze-preserved for 24 months

SummaryPlants have been regenerated from cultures of potato meristems freeze-preserved in liquid nitrogen (−196°C) for 24 months. The implications and the feasibility of employing cryogenic methods for the long-term conservation, and international exchange of germplasm of potato, and other vegetatively propagated crops are pointed out.

Technology and prospects of cryopreservation of germplasm

SummaryEntire plants have recently been regenerated from frozen cultures of protoplasts, cells, tissues and organs and stored at super-low temperatures for various lengths of time. This suggests the possibility of utilizing cryogenic methods for the conservation of important and rare germplasm, especially of the vegetatively propagated plants, which at present do not have any satisfactory method for their preservation. In addition, the freeze preservation offers a number of significant uses and prospects; (i) tissue cultures often show chromosomal variations, nuclear and ploidy changes, and mutations. Such genetic variables and cell lines which do not occur in nature can be picked out, banked and used in response to research needs; (ii) to maintain a cell line, it has to be transferred to a fresh medium periodically; the freeze storage would suppress cell division and thus the need for subculturing is avoided; (iii) at super-low temperatures the cells are in a non-metabolic state, which delays or virtually stops the ‘ageing’ process, and thus the morphogenetic potential of cultures is retained; (iv) pathogen-free stocks could be frozen, revived and propagated when desired, this would be ideal for the international exchange of such materials; and (v) the freezing of pollen would solve some of the problems encountered with the incompatibility and pollen longevity.Ever increasing population pressures demand improving and evolving new cultivars. However, with this enthusiastic search for obtaining new plants, and rapid increase in their number, it is not only becoming difficult but at times impossible to maintain or preserve some of the stocks which at present, are not needed for breeding purposes. Thus, some of the germplasm which may not seem to be of importance today, but might be needed in future, is ignored or completely lost. Therefore it is for the purpose of preservation of materials which are threatened with extinction that ‘Germplasm Banks’ need to be established.It is envisaged that freeze storage and tissue cultures would be a meaningful tool in experimental biology and agricultural research for the preservation and international exchange of important and pathogen-free germplasm.

Interspecific hybridization of Brassica napus and B. juncea through ovary, ovule and embryo culture

SummaryEmploying in vitro culture of ovaries, ovules and embryos, interspecific hybrids have been obtained amongst two important oilseed crops, Brassica napus x B. juncea and their reciprocal. The test-tube hybrid plants have been transferred to the field, and reared to maturity. The F1 seeds obtained from the hybrid ovaries showed normal germination, and the hybrid plants exhibited a range of variation of characters.

Interspecific hybridization inBrassica juncea × Brassica hirta using embryo rescue

SummaryInterspecific hybrids have been obtained in an otherwise incompatible cross betweenBrassica juncea × Brassica hirta through the in vitro culture of hybrid ovules and ovaries. The best response was observed from ovules and ovaries cultured 10–15 and 5–7 days after pollination respectively on a basal medium supplemented with indoleacetic acid, kinetin and casein hydrolysate. In some cases the basal cut end of the ovaries proliferated to form callus and shoots. The in vitro-derived hybrid seeds varied in their colour, size and shape, and the F1 plants in the field showed a large diversity in their morphological traits. The hybrids were sterile, and had an intermediate number of chromosomes (2n=30).

Hybridization between diploid (Gossypium arboreum) and tetraploid (Gossypium hirsutum) cotton through ovule culture

SummaryWith in vitro culture of ovules, interspecific hybrids have been obtained in an otherwise incompatible cross between a diploid (Gossypium arboreum) and a tetraploid (G. hirsutum) cultivated cotton. The early abortion of the embryo was prevented by repeated treatment of the flowers, immediately after pollination with a solution of gibberellic acid and naphthalene acetic acid. The ovules excised three days after pollination and cultured in a liquid medium underwent profuse proliferation, whereas on an agar-solidified medium supplemented with casein hydrolysate, indoleacetic acid and kinetin they germinated to form hybrid plants.

In vitro induction of genetic variability in cotton (Gossypium spp.).

SummaryThrough the in vitro culture of excised embryos and ovules, interspecific hybrids have been obtained from cultivated and wild species of Gossypium. The hybrids matured upon transfer to the field. The anthers, ovules and embryos from both the diploid (2n=26) and tetraploid (2n=52) species underwent proliferation, and this response was genotypic. The diploid species invariably showed profuse callusing in comparison with the tetraploid. The callus showed various chromosome numbers, ranging from haploids to hexaploids, and from high polyploidy to aneuploidy. Hybrid callus culture may augment the genetic variability by providing a means for obtaining genetic exchange in interspecific hybrids. The implications of the in vitro induction of genetic variability for cotton improvement are discussed.

Interspecific hybridization in the genus Arachis through embryo culture

SummaryThe embryos of a cultivated tetraploid peanut (Arachis hypogaea), a wild diploid species (A. villosa), and their hybrid embryos, which generally abort in nature, were cultured in vitro and the plants have been successfully transferred to the soil. The hybrids showed triploid chromosome number (3x=30). The significance of wide hybridization in peanut-improvement programs is discussed.

INTERSPECIFIC HYBRIDIZATION IN THE GENUS GOSSYPIUM THROUGH EMBRYO CULTURE

SummaryWith embryo rescue and culture techniques interspecific hybrids have been obtained amongst diploid cultivated (Gossypium arboreum, G. herbaceum) and wild species (G. stocksii, G. anomalum) of cotton. The early abscission of the young bolls was prevented by repeated application of growth regulators followed by the culture of immature hybrid embryos (15 days after pollination). The best growth and development were obtained on modified Murashige and Skoogs medium with supplements. The plants were stouter when the cultures were first incubated in the dark for 15–25 days, followed by exposure to light. The hybrid plants transferred to soil developed further and matured, and were more or less intermediate between their respective parents.

Regeneration of genetically diverse plants from tissue cultures of forage grass — Panicum sps

SummaryCallus tissue cultures of 3 species of forage-grass (Panicum) were established from the excised embryos, shoot tips, and segments of young inflorescences, and induced to regenerate plants showing genetic diversity. These plants were transferred to the soil, and reared to maturity. The importance of in vitro methods for increasing the reservoirs of germplasm in forage-improvement programs is emphasized.

Hybridization in Brassica juncea × Brassica campestris through ovary culture

SummaryOvary culture has been employed for the production of interspecific hybrids of a partially compatible cross of Brassica juncea (2n=36) × Brassica campestris (2n=20). Five to seven days old ovaries cultured on Whites medium supplemented with casein hydrolysate (300 mg/l) and sucrose (5%) produced more seeds than any other media tried, but seed development was better on media fortified with plant hormones. The seed yield was better in B. juncea × B. campestris than their reciprocal cross. The plants obtained from ovary-derived seeds were transferred to the field; they were intermediate in some morphological characters and chromosome number (2n=28) as compared to their parents. The flower buds generally did not open and had poorly developed anthers with mostly sterile pollen. The pod size/setting was very much reduced, but healthy seeds were obtained.