About fifty species of plants have been transformed. Some are inherently easier to transform than others. Tobacco, for example is probably the easiest species to transform. The success of transformation procedures in many crop plants is proportional to the time scientists have spent on them. Corn is a very economically valuable crop. Therefore a greater proportion of research dollars have been spent on corn transformation research. This has resulted in a higher success in corn transformation than in soybean, wheat or sorghum transformation. What is true of all transformation procedures is 1) they involve a mix of ’art’ and science. The same procedures may not work equally in the hands of all scientists, and 2) they are labor intensive and thus expensive.
Obviously, the goal of a genetic engineer is to reliably generate as many transgenic plants as possible. Most genetic engineering laboratories try to become efficient at using one method of transformation and stick with that. Sometimes their decision of which method to use is dictated by patent rights associated with the different methods. University and USDA genetic engineers have the primary mission of studying how the transformation process works. They are also more likely to commit their efforts on crops that industry dedicates less time to, such as sorghum.
All transformation procedures are most successfully used when the law of averages is incorporated into the process. The actual insertion of DNA into a plant chromosome is poorly understood. Scientists who are best at the technical merging of the gene delivery techniques with the culture of plants regeneration from cells that have been transformed will have the most successful transformation systems. As our knowledge of the process improves, the procedure may become more like engineering. For now, it is much less predicatable than the name implies.