Abstract
A number of factors that have been reported to affect transformation/regeneration rate in plants were studied in multiple eucalypt genotypes. These include surfactant, acetosyringone, fipexide, basal media, activated charcoal, ascorbic acid, lipoic acid, proline, cytokinins, sugars, spectinomycin selection, Agrobacterium strains and concentrations, forchlorfenuron, PVP, silver nitrate, and explant heating prior to cocultivation. Heating, use of acetosyringone, basal medium, cytokinin type, carbon source, and Agrobacterium strain had substantial impacts—whereas the other factors studied had negligible or a negative impact. In search of a model genotype for producing transgenic shoots, 53 diverse genotypes that included E. grandis, E. grandis x E. urophylla , E . urophylla x E. grandis, and E. dunnii, were screened using a highly infective gall-causing Agrobacterium strain with T-DNA genes isolated from strain C58. One E. grandis x E. urophylla genotype was identified, Egu45-1, that showed a regeneration rate of transgenic shoots of 4% to 8% (frequency of explants that produced one or more transgenic shoots). This genotype and the associated transformation protocol will be made available to any interested party without restriction.