Development of Two Screening Methods for Tomato Seedlings Containing the NPT II Selectable Marker Gene
Two simple, cost-effective methods to screen fresh-market tomato seedlings containing the kanamycin resistance gene construct, in which the nopaline synthase promoter from pMON128 is driving the NPT II gene, have been developed. The assays can reliably distinguish kanamycin-resistant from sensitive progeny for a variety of tomato genotypes. One method is an in vitro germination assay. Two selective agents, geneticin (G418) and kanamycin sulfate, were evaluated for their efficacy, and titrations were performed to determine the optimal concentration of the appropriate agent. The second method is a whole-plant spray test of seedlings to identify kanamycin-resistant progeny. A protocol was developed that could distinguish positives from negatives in 5 weeks. Currently, these assays are being used to screen R1 progeny rapidly to identify positives and obtain segregation ratios. They also are being used to screen R2 progeny to identify quickly those lines that are “true-breeding” or homozygous for field trial evaluation.