Biotechnological approaches for crop improvement in ornamental crops
Ornamental plants are produced mainly for their aesthetic value, thus the propagation and improvement of quality attributes such as leaf types, flower color, longevity and form, plant shape and architecture, and the creation of novel variation are important economic goals for floriculturists.
The introduction of various in vitro techniques has revolutionized the horticulture sector in India in recent years. The greatest stimulus provided by the tissue culture technology lies in increased speed of clonal multiplication of shoot meristem culture of highly desired strains of plant material besides freeing the clonal material from pathogens. The three major areas of bio-technology, which can help us in crop improvement in general and floriculture in particular are micro propagation systems, including tissue culture, genetic engineering and new methods of in vitro hybridization and recombinant DNA technique
In vitro culture:
In vitro culture is one of the key tools of plant biotechnology that exploits the totipotency nature of plant cells, a concept proposed by Haberlandt (1902) and unequivocally demonstrated, for the first time, by Steward et al. (1958). Tissue culture is alternatively called cell, tissue and organ culture through in vitro condition (Debergh and Read 1991). It can be employed for large-scale propagation of disease free clones and gene pool conservation.
Tissue culture is a means of preserving species that are rare and threatened and providing an alternative source of plants for commercial, horticultural and traditional medicinal trade. Tissue culture is the “aseptic culture of plant protoplasts, cells, tissues or organs on a culture medium which is as defined as possible; the cultures are maintained under controlled environmental condition”. Tissue culture consists of growing plant cells as relatively an organized masses of cells on an agar medium (callus culture) or as a suspension of free cells and small cell masses in a liquid medium (suspension culture). Tissue culture is used for vegetative multiplication of many species and in some cases for recovery of virus-free plants. It has potential application in production of somatic hybrids, organelle and cytoplasm transfer, genetic transformation and germplasm storage through freeze-preservation. The in vitro culture of cells, tissues and organs of plants has a great potential to generate improved crop plants and ornamentals. Micropropagation is undoubtedly the most familiar application of plant biotechnology.
The technique offers not only means for mass propagation but also plays an important role to conserve elite or rare plants that are threatened with extinction. Orchids were, in fact, the first plants to be propagated commercially utilizing in vitro methods. Presently this technique is being commercialized in rose, gladiolus, anthuriums, etc. Micropropagtion is production of large number of clonal progeny through tissue culture.
Plan tissue culture:
The production of exact copies of plant that produce particularly good flowers or desirable traits
To quickly produce plant lets
Multiplication of plants in the absence of seed
Regeneration of whole plants form plant cells that are genetically modified
Diseased free stocks particularly viral free seedlings
Chrysanthemum can be multiplied at a fast rate by cultivating shoot apex in vitro from somatic callus, peduncle and other floral parts and from leaves. Higo-chrysanthemum were regenerated form florets of 3 line cultured in vitro. In rose dormant auxiliary buds are more suitable for in vitro culture than shoot tips.
Recovery of virus free stocks: virus infections spread rapidly in vegetatively propagated crops. In chrysanthemum clonal propagation through meristem culture in vitro resulted in production of disease free plant let which are resistant to important virus (TSWV) and viroid like chrysanthemum stunt viroid (chSv)
Recovery of distant hybrids are done through embryo culture. When distant species or genera are crossed abortion of endosperm will occur and lead to death of young embryos. So in such cases, young embryos are excised before endosperm abortion and cultivated in vitro to obtain plant lets. Eg: R. spinosissima x R. foetida R. nutkana x R. acicularis R. pendulina x R. rugosa
Recovery of haploids plants from interspecific cross: individuals having the gametic chromosomes number of the species are called haploid (n). haploids are produced in nature though parthenogenesis, anther culture, interspecific crosses, culturing of unfertilized ovaries, X- irradiated pollen etc.,
Orchid breeding: Orchids lack endosperm and in many orchids the embryos are not fully developed. So it’s easy to obtain seedlings by embryo culture
this has enable the transfer and expression of a desirable gene from any organism in to the plant. Integration of specifically desired traits through genetic engineering has been possible in some flower crops. Recent advancements in molecular biology and genetic transformation have made it possible to identify, isolate and transfer desirable genes from any living organism to plants.
Using traditional breeding methods, breeders have been able to create new varieties that have desirable traits but it has its limitation. One of the main disadvantages of traditional breeding is the limited gene pool in any single species. In addition, heterozygous nature of the materials makes the lack of success of traditional techniques in breeding an orange petunia or a blue rose.
Flavonoids, caratenoids and betalains are major floral pigments. Among these three flavonoids contribute most of the range and type of coloured pigment in plants. Flavoinds consists of more than 10 class of components.
orange, red magenta, violet and blue colours Aurones and chalcones: yellow Flavones and flavonols: colourless and pale yellow
The flavonoid biosynthetic pathway leading to floral pigment accumulation have been well characterized. By using genetic engineering technique have primarily targeted the flavonoid pathway to alter flower colour. Using this technique blue rose have been developed.
Blue rose: Blue rose is believed to be the symbol of love and prosperity. It does not occur in nature and they were created by dying white roses with blue colour. In 2004 researchers have used GM to create blue rose. It is a collaborative research by Australian company Florigen and Japanese company Suntory. They have inserted a gene for the plant pigment delphinidin cloned form petunia and inserted to the old garden rose.
Initially obtaining exact blue was difficult because of present of pigment cyaniding. So by using RNAi technology they have depressed the production of cyaniding and bale to produce Mauve colour flower.