Somaclonal variation

• The genetic variability present among the cultured cells, plants derived from such cells or progeny of such plants is called somaclonal variation.
• The plants derived from cell and tissue cultures are termed as somaclones and the plants displaying variation as somaclonal variants.
• Somaclonal variation may occurs either for single trait (or) more than one trait at a time.
• Somaclonal variation may occur due to chromosomal abnormality in cultured cells and plants regenerated from them.
• The chromosomal abnormality may be due to changes in chromosomal number (ploidy level) and chromosomal structure.

Types of somaclonal variation

a) Gametoclonal variation : variation observed among the plants regenerated from gametic cultures. Eg: Adroclonal variation (pollen) and Gynoclonal variation (ovule).

b) Protoclonal variation: – variation observed among the plants regenerated from protoplast cultures.

c) Calliclonal variation: – variation observed among the plants regenerated from callus cultures.

Factors affecting somaclonal variation

a) Species and genotype: Vegetatively Propagated > sexually propagated.

b) Ploidy level: positive correlation between ploidy level and variation eg barley 1%, wheat 40%.

c) Source of explant: petiole is preferred to stem.

d) Tissue culture technique: protoplast more, than others.

e) Duration of cell culture: positive correlation.

Application of Somaclonal variation

a) Isolation of regenerants resistant to diseases.

b) Isolation of variants resistant to abiotic stresses

c) Cell lines resistant to chilling have been isolated in several cases. Eg: -Chillies, Nicotiana sylvestris.

d) Development of varieties with improved seed quality. A variety Ratan of Lathyrus which has low neurotoxin content has been develop through somaclonal variation

e) Stress resistance

f) Crop improvement

g) Mutant isolation

others

a) Novel variants from agronomic traits (Cotyledon color).

b) Disease resistant variants: maydis in maize.

c) Abiotic stress variants: salt tolerance in rice.

d) Herbicide resistance varieties: Glyphosphate in tomato.

e) Insect resistance varieties: Aphid in wheat.

f) Seed Quality:

g) Alien gene integration

Approaches to isolation of somaclonal variation

1. Screening: observing large cells to variations.
2. Cell selection: Selecting only the qualitative cells.