Genotype-dependent stable genetic transformation in German spring wheat varieties selected for high regeneration potential

Five commercial German spring wheat cultivars (Triticum aestivum L.), four of them selected for high regeneration potential, were used fbr particle bombardment of embryogenic scutellar calli with plasmid pAHC25 containing the bar and the uidA gene, each under the control of the maize ubiquitin-1 promoter. In transient expression of uidA, no statistically significant differences between the varieties used could be detected. From four of the cultivars used, 16 transformants were obtained. Variety <Combi> showed the highest transformation frequency (0.96%), followed by <Turbo> (0.58%), <Hanno> (0.48%) and <Naxos>, (0.15%). <Thasos>, proved to be recalcitrant. At least one copy of both the uidA and the bar gene had been integrated into the genome of each transformant. The bar gene was expressed in all T-0-plants, whereas the uidA gene had been silenced in 4 of them. From most transformants the transgenes were transmitted unchanged in a Mendelian manner to the T-1- and T-2-generations, and their expression was maintained. Only three transformants were unstable. In the T-1, they had lost either the bar or the uidA gene. In all of the other T-2- and - first results - Ts-generations, the transgenes proved to be stable, and no additional silencing was observed. The data indicate stable transformation in most of the commercial varieties used. In addition, two more general conclusions can be drawn: First, in comparing the present data with the results of earlier Agrobacterium-mediated gene transfer attempts, using the same wheat variety <Turbo> and the same coding regions, convincing evidence for the superiority of biolistic methods in wheat transformation could be obtained. Second, there was no parallelism between the frequencies of regeneration and transformation, indicating genotype dependent transformation potentials.