Accelerated production of transgenic wheat (Triticum aestivum L.) plants.

We have developed a method for the accelerated production of fertile transgenic wheat (Triticum aestivum L.) that yields rooted plants ready for transfer to soil in 8-9 weeks (56-66 days) after the initiation of cultures. This was made possible by improvements in the procedures used for culture, bombardment, and selection. Cultured immature embryos were given a 4-6 h pre-and 16 h post-bombardment osmotic treatment. The most consistent and satisfactory results were obtained with 30 μg of gold particles/bombardment. No clear correlation was found between the frequencies of transient expression and stable transformation. The highest rates of regeneration and transformation were obtained when callus formation after bombardment was limited to two weeks in the dark, with or without selection, followed by selection during regeneration under light. Selection with bialaphos, and not phosphinothricin, yielded more vigorously growing transformed plantlets. The elongation of dark green plantlets in the presence of 4-5 mg/l bialaphos was found to be reliable for identifying transformed plants. Eighty independent transgenic wheat lines were produced in this study. Under optimum conditions, 32 transformed wheat plants were obtained from 2100 immature embryos in 56-66 days, making it possible to obtain R3 homozygous plants in less than a year.