1. Introduction

Genetic selection of transformed cells is a significant step of any plant transformation. Screening of transformed cells or plants for gene integration and expression in transformed cells or plants is a process that involves several techniques, including DNA and RNA blot hybridization analysis, PCR, ELISA analysis. In the absence of a correct selection system one would face with the option of screening every shoot that regenerates in a transformation experiment. In cases where transformation frequency is high this may be possible but for plant species that transform with low frequencies this would be a laborious, if not impossible, task. Therefore, a selectable marker gene (Table 27.1) is incorporated into the plant transformation vectors and an appropriate selecting agent is added to the culture medium which favors the growth of only transformed cells. The genes used as selectable markers are dominant and typically of bacterial origin. For successful selection, the target plant cells must be susceptible to moderately low concentrations of the selecting agent in a non-leaky way. The compound that inhibits the growth but does not kill the wild type cells is preferred as a selecting agent in plant transformation. The concentration of the selecting agent used varies widely depending on the sensitivity of the plant species and/or explant source.

Table 27.1 : Selectable marker genes used in plant transformation