Somaclonal Variation for Salt Tolerance in Rice

Abstract

Somaclonal variation for plant improvement is among the most important developments in the agricultural application of this technology; rates of mutation in existing genes have been increased and even new genotypes not found in nature have been engineered. Negative selections using agents such as antibiotic drugs, analogs of metabolic compounds, or simply NaC1 are widely used. The selection of salt-tolerant characteristics is relatively simple, especially if compared to the selection of other characteristics such as high seed protein or disease resistance. However, the main problem in the selection process is the low rate of plant regeneration from different forms of cell aggregates derived from cultured explants. This bars the use of large numbers of regenerants for mass selection. Other problems arise because of the lack of information on what mechanisms produce salt tolerance in cells, tissues, and at whole plant levels. There is also the difficulty of conserving other characteristics of the original varieties in plants selected for their tolerance of salt. The ideal occurrence is a single gene mutation for salt tolerance at a specific locus, which does not involve a chromosome rearrangement in a given adapted variety. This can be achieved through selection of variants resulting from soma-clonal material in vitro in the form of protoplast, cell colony, or callus. Even the selection of entire plants in natural conditions becomes possible, or a combination of these uses, followed by conventional breeding processes.