William S - I think you mean potato, not tomato.
If you mean Defender, that has a single R gene (R1). At best it has medium resistance which can be overcome. I would need to look up Elba, as it is a European potato and may not be available in the US. There are better ones out there for breeding with, especially if you want to look outside the pool of cultivated potatoes. What you ideally want is durable field resistance, meaning the plant is not affected. There are very few potatoes with what is considered durable field resistance, but there are a few available to potato breeders through the USDA genebank. One of the problems with breeding tetraploid potatoes is that most potatoes descended from them will segregate for the genes present in the parents. Achieving homozygosity in tetraploids is difficult and may take many years and thousands of plants, potentially.
This article has a brief summary history of available R genes for LB resistance, and where efforts are heading with breeding work, and why potatoes with single R genes, or sometimes multiple R genes are overcome. I would recommend downloading the PDF.
https://www.sciencedirect.com/science/article/pii/S1876610212003049Regarding multiple gene potatoes, the following article (again, download the pdf) explains some of the details and surprisingly, discusses that there are other factors in play other than just R genes.
https://www.researchgate.net/publication/296623252_The_Adoption_of_Cv_Igorota_in_the_Philippines_and_Vietnam There is a chart that compares several potatoes including Igorota and Favorita. Igorota, grown in the Phillipines, has near durable field resistance, while Favorita is susceptible, but they share the same two R genes, so there obviously are other genes at work providing resistance that are not identified. Cooperation88 is a CIP bred potato that so far has provided durable field resistance in China, and has at least 4 major R genes. The same two as Igorota, plus two others. Igorota and Cooperation88 are from similar LB breeding populations.
There are also potato lines that have resistance to LB, but no known R genes. Those are the ones that interest me the most at this point.
I'll post in more detail later after I compile some of my notes.