Chromosome-mediated Transformation via Microinjection

Many economically important plant characteristics such as drought tolerance are encoded by multiple genes or polygenes. Individually, polygenes exert very little effect on the phenotype [14]. These genes can either occur scattered throughout the genome or clustered within blocks. The genetic methods for analyzing polygenic traits have been thoroughly developed [17]. The prohibitively large number of generations (~>25) required for genetic analysis, however, precludes applying these methods to most higher plant species. Current gene transfer methods can successfully transfer single genes. For example, the Ti plasmid of Ag r obac t e r i um tume fac i ens has been used to transfer 14 kilobases of DNA [2]. However, a single polygenic trait could contain up to 20 individual genes comprising 500 kb of DNA. Most plasmids could not con-