somaclonal

Somaclonal variation refers to heritable genetic and epigenetic differences that arise among plants regenerated from somatic tissue culture compared with the donor plant. The variation can occur in plants produced through callus culture, shoot regeneration, protoplast fusion, or other in vitro methods. It encompasses genetic changes, such as point mutations, chromosomal rearrangements, aneuploidy or polyploidy, as well as epigenetic alterations including changes in DNA methylation and chromatin structure, often associated with transposable element activity. Factors contributing to somaclonal variation include the duration of tissue culture, the type and concentration of plant growth regulators (auxins and cytokinins), osmotic stress, and other culture conditions; environmental stress can activate mutational and epigenetic processes. The rate and spectrum of variation depend on species and genotype, explant source, culture duration, and media composition.

Manifestations of somaclonal variation range from subtle biochemical differences to visible phenotypic changes such as plant height, leaf morphology, flowering time, yield, or disease resistance. Some variations are stable and heritable through vegetative propagation or seeds, while others may be transient. Detection relies on phenotypic screening and molecular techniques, including RAPD, AFLP, SSR, or SNP markers, as well as cytogenetic analyses and methylation-sensitive assays like MSAP or bisulfite sequencing.

Applications and implications: somaclonal variation can be a useful source of novel traits for plant breeding or crop improvement, but it can also undermine genetic fidelity in clonal propagation programs. Researchers study somaclonal variation to understand stress responses, genome stability, and epigenetic regulation in tissue culture. Field validation is typically required to confirm trait value before commercial adoption.