Elementary plant Biochemistry and Biotechnology (2+1)

Applications

1. Production of doubled haploids: Homozygous lines of the cross pollinating species and hybrids are highly desirable to increase the efficiency of selection and production of homozygous plants. The conventional method to produce homozygous plants is lengthy and laborious, requiring 7-8 recurrent cycles of inbreeding. Moreover, this approach is impractical for self-incompatible and male sterile and tree species. On the other hand, homozygous plants can be obtained in a single generation by diploidization of the haploid. This kind of production of stable, homozygous dihaploids (DH) in a single generation equivalent to the F α generation of pedigree breeding and thus considerably shortens the breeding cycle. Generally, colchicines is recommended to diploidize the pollen plants. In practice, the pollen derived plants are immersed in filter sterilized solution of colchicines or applied as lanolin paste or injecting into the secondary buds or by root feeding. Besides bringing about chromosome duplication, colchicines treatment may also result in chromosome and gene instabilities. Therefore, the frequent occurrence of spontaneous duplication of chromosomes in differentiated plant cells (cortex, pith) and callus cells in long term cultures has also been exploited to raise homozygous fertile diploids from haploid plants (Figure). In this method, pieces of vegetative parts such as stem, root or petiole segments are cultured in a suitable medium to induce callusing. The initial callus may have some diploid cells but their frequency would increase in repeated subcultures. Such calli are transferred to the plant regeneration medium. Many of the plants so derived are diploid. However, the ploidy of individual plants must be confirmed before incorporating them in further experiments.
2. Normally, in a hybridization programme evaluation of lines is possible only after 4-5 years of backcrossing (F5 or F6 generations) and it takes another 4-5 years to release a new variety. By anther culture of F1 hybrids the various genotypes of gametes can be fixed and evaluated in the first generation. Anther culture can itself generate new recombinations and fix them simultaneously.
3. Haploids are extremely useful for detecting recessive mutants which may not express themselves in the heterozygous diploid background and therefore can be easily lost.
4. Gametoclonal variation –in vitro androgenesis provides a unique opportunity to screen the gametophytic variation caused by recombination and segregation during meiosis. For example, a gametoclone of tomato, which bears fruits with higher solid content than the parent cultivar, has been produced through anther culture.
5. Mutagenesis- Detection and isolation of recessive mutants in the haploid state and rapid obtainment of the mutated gene in a homozygous diploid state is a special merit of haploidy in higher plants. Application of mutagenic treatment at the microspore stage, which is a single celled structure, has the added advantage of obtaining solid mutants. Through, microspore mutagenesis, a mutant of Brassica napus with high oleic and low lanoleic acid content was obtained.
6. Production of super male of Asparagus officinalis- In A. officinalis, a dioecious crop species, an inbred population is produced through sib crosses between pistillate and staminate plants which yield 50 % males and 50 % females. However, the commercially desirable features of this crop are uniform male population with spears having low fibre content. Anther culture was used to produce haploids of this species and this was diploidized to raise homozygous males. These are called as super-males

Limitations

1. Low Yield- generally 5-8% of the total pollen grains in a responding anther undergo androgenic development.
2. 70-80% of the embryos are incapable of normal germination due to structural, physiological and biochemical abnormalities of pollen.
3. Occurrence of high frequencies of albinos in cereals.
4. Instability of genetic material during androgenesis.