Selection of Radiation-induced Salt Tolerant Rice Mutants by in vitro Mutagenesis

Abstract

Radiation induced mutagenesis has been studied extensivelyfor the identification and isolation of a plant gene and inplant breeding programs. Rapid progress in plant tissue culturemethods is attributed to the availability of many mutantsthat can be generated for specific biochemical events thatare difficult or impossible to use with intact plants (Carlson1970; Larkin and Scowcroft 1981; Schaeffer and Sharpe1983; Kim et al. 2004). This may be achieved by co-culturingplant tissues with pathogens or their toxins and by manipulatinga medium composition, e.g. selection for a resistanceto salinity, drought and amino acid analogs. Although,it is possible to select mutants with a salt tolerance by asomaclonal variation, mutant frequencies are often lower inplant systems due to inefficient recovery techniques, as wellas the presence of multiple gene copies located on differentchromosomes, and by cell-to-cell interactions in even themost ideal suspension culture systems (Schaffer and Sharpe1983). Therefore, in vitro mutation induction techniques providetools for a rapid creation and increase of the selectionfrequencies of cell types for which there is no obvious counterpartin field environments (Maluszynski et al. 1995). Suchtechniques enable a greater use of mutated genes for a cropimprovement, the cumulative effect of which may result ina more desirable character than the original variety. Rice, animportant staple food, is consumed by more than half of theworld’s population. It is sensitive to a salt stress; therefore,development of varieties with an increased salt tolerance isrequired. The possibility of a screening for a salt stress in aculture makes in vitro methods attractive for developingstress tolerant plants (Lee et al. 2003). In the present protocol,we described the selection of salt tolerant cell lines viain vitro mutagenesis, regeneration, a consecutive selectionthrough each generation (M2-M3), and a screening of salttolerant lines in a saline field. Fig. 1 shows a flow chart ofthe procedures for the selection of the salt tolerant lines.