GENETIC-TRANSFORMATION OF SWEET-POTATO BY PARTICLE BOMBARDMENT

Transient and stable expression of foreign genes has been achieved in sweet potato using the particle bombardment system of gene delivery. C allus and root isolates of two genotypes (Jewel and TIS-70357) with po sitive signs of transformation have been recovered. Tungsten microcarr iers coated with plasmid DNA (pBI221 containing the gusA gene) were ac celerated at high velocity using a biolistic device into sweet potato target tissues. Histochemical examination of bombarded leaf and petiol e explants revealed that most had cells expressing the gusA gene. When explants were cultured, calli and roots developed in most bombarded t issues. Similar results but with a lower frequency of transformation w ere observed when the plasmid pBI121 (with gusA and antibiotic resista nce nptII genes) was employed and bombarded explants cultured on an an tibiotic selection medium. Subcultured roots and calli were positive f or gusA expression when tested even after one year of in vitro culture , and thus the expression of the foreign gene is fairly stable. The pa rticle bombardment approach of gene delivery appears to have a potenti al for generating transgenic sweet potatoes with useful agronomic trai ts.