How about this one: Constitutive expression of the virulence genes improves the efficiency of plant transformation by Agrobacterium. Hansen G, Das A, Chilton MD. Proc Natl Acad Sci U S A. 1994 Aug 2;91(16):7603-7. And a recent one: The efficiency of Arabidopsis thaliana floral dip transformation is determined not only by the Agrobacterium strain used but also by the physiology and the ecotype of the dipped plant. Ghedira R, De Buck S, Nolf J, Depicker A. Mol Plant Microbe Interact. 2013 Jul;26(7):823-32. doi: 10.1094/MPMI-11-12-0267-R.