Cell and Tissue Culture Approaches in Relation to Crop Improvement

Abstract

Plant cell and tissue culture involves the growing of cells, tissues and organs on synthetic medium under closely controlled and aseptic conditions. Plant cell and tissue culture methods offer a rich scope for the creation, conservation and utilization of genetic variability for the improvement of field, horticultural and forest plant species. Micropropagation of selected plant species is one of the best and most successful examples of the commercial application of tissue culture technology. Micropropagation ensures true-to-type, rapid and large-scale multiplication. Now scores of multimillion-dollar industries around the world propagate a variety of plant species through micropropagation. Tissue culture technology offers environmental-friendly industries to flourish. It is likely that automation of multiplication systems will be commercially feasible within the next few years for several species including potato microtubers, lily bulblets and gladiolus corms. Meristem culturing and in vitro grafting help in developing disease-free plants. Improvement of somatic embryogenesis, coupled with embryo desiccation and encapsulation technology, may lead to the utilization of ‘artificial seeds’ for mass cloning of plants. Further induction of somatic embryogenesis in plants helps in cloning and transformation. Somaclonal variation is a potent emerging aspect for broadening the genetic base and thus obtaining incremental improvement in the commercial cultivars, more particularly, in the vegetatively propagated plant species. Using the technique of in vitro selection, many million cells/protoplasts can be screened against various biotic and abiotic stress factors in a single Petri dish which is more efficient as compared to the screening of similar number of plants in the field which requires more time and space as well. Production of haploids through bulbosum, anther/pollen culture and embryo rescue from wide hybrids has been exploited for the production of haploids/doubled haploids for early release of varieties. These methods ensure true-breeding (doubled haploids) plants in less than 1 year, which are otherwise obtained after seven to eight generations through conventional methods. Since the possibility of producing useful secondary products in plant cell cultures was first recognized in the 1970s, considerable progress has been made, and a number of plant species have been found to produce secondary products such as shikonin, diosgenin, caffeine, glutathione and anthraquinone. Embryo culture is the practical approach to obtain interspecific and intergeneric hybrids among otherwise difficult to cross parents. It has been successfully used to transfer desirable genes from wild relatives into cultivated varieties of several field and vegetable crops. Somatic cell hybridization helps in combining characteristics even from otherwise sexually incompatible species and to obtain cybrids and organelle recombination not possible through conventional methods. In vitro freeze storage and cryopreservation are very important techniques for germplasm conservation especially of the vegetatively propagated crops. Plants have been successfully regenerated from tissues cryopreserved at –196 °C in liquid N2 for several months to years in several crops. During the past 25 years, the combined use of recombinant DNA technology, gene transfer methods and cell and tissue culture techniques has led to the efficient transformation and production of transgenics in a wide variety of crop plants. In fact, transgenesis has emerged as an additional tool to carry out single-gene breeding or transgenic breeding of crops.