EFFECT OF AGROBACTERIUM GROWTH STAGE AND CULTURE DENSITY ON THE TRANSFORMATION EFFICIENCY OF SWEETPOTATO

The efficiency of genetic transformation of plants via Agrobacterium cocultivation is determined by several factors. This experiment aimed to study whether the culture age and bacterial density of Agrobacterium tumefaciens influenced the transformation efficiency of sweetpotato ( lpomoea batatas ). The A. tumefaciens (MP90 gus::nptII ) was cultured in LB broth (10 ml) and resuspended in half -strength MS solution prior to use. Petiole and leaf lamina explants of cultivars Regal and Rojo Blanco were cocultivated with the bacterial cultures that were 6-32 hour old. The age of the Agrobacterium culture used for cocultivation had a significant effect on the extent of explant area transformed. Cultures that were 24 h old (4×10 9 CFU/ml) produced the highest transformation. When cultures of various ages were diluted 1, 5 and 10 times (prior to cocultivation), the extent of transformation was not significantly affected. Thus, high dilutions (up to 10 times) could be used in the sweetpotato transformation to minimize the bacterial overgrowth on the explants duing subsequent incubation. Petioles were generally more competent to transformation and had proportionately larger transformed areas when compared to leaf lamina.