Examination of Factors Affecting Transformation of `McIntosh' Apple by Agrobacterium tumefaciens

The overall goal of our research is to develop an efficient transformation and regeneration system for `McIntosh' apple. The first objective was to determine the optimum combination of Gelrite (G) and agar (A) to maximize regeneration and minimize vitrification. Treatments included the following combinations of agar (in g–liter–1) and Gelrite (in g–liter–1): 1) 7 and 0; 2) 5.25 and 0.625; 3) 3.5 and 1.875; 4) 1.75 and 1.875; and 5) 0 and 2.5. There were 10 replications, and a single petri plate containing six leaf pieces was the unit of replication. Both 5.25(A) and 0.62(G) and 3.5(A) and 1.25(G) provided high regeneration of healthy, nonvitrified shoots. Since modification of media affects the concentration of antibiotics used in selection due to precipitation of antibiotics, the second objective was to determine the optimal concentration of antibiotic for the selection and regeneration of transformed `McIntosh' on gelrite–agar-based media. Kanamycin was tested at 0, 10, 25, 50, 75, and 100 μg–ml–1 and paromomycin was tested at 0, 50, 100, 150, 200, and 250 μg–ml–1. Antibiotic selection will be discussed relative to optimum concentration and efficiency of selection.