What would enable someone to reproduce the tree from scratch, and continue developing that line of trees, using tools common to apple tree breeders? I’m not an apple tree breeder, but I suspect that’s the seeds. Maybe the genetic sequence is like source code in some analogical sense, but unless you can use that information to produce an actual seed, it doesn’t qualify in a practical sense. Trees don’t have a “compilation phase” to my knowledge, so any use of “open source” would be a stretch.