KeithB said: I just wonder which of the initial seed purchases from Lily Auction or EBay carried the genes, and why they appeared only on second or third generation crosses.
The most likely reason that white seeds only appeared on second or third generations crosses would be that the genetics of white seeds is recessive. It is also rare. So the few daylilies that have the gene (formally it is the allele) are heterozygous. The second part is that the outer seed layers are not determined by the seed but by the pod parent. So a genetically white seed w/w (for diploids) would usually be the normal black colour. A genetically w/w pod parent would produce white seeds when crossed with any pollen parent but in most cases all the white seeds would actually be genetically W/w.
The parents of such plants would usually be W/w and produce normal coloured black seeds. Those seeds produced by a cross of W/w X W/w would be 1/4 WW 1/2 Ww and 1/ww. But all those seeds would be black. Since the allele for white seeds is rare then heterozygous daylilies (W/w) are also rare. Your initial seeds purchases might have had only one W/w seed. Possibly there might have been one seed purchase that had more than one W/w seed. However, even when a cross is by chance W/w X W/w only one in four of the seeds produced can be expected to be w/w and produce white seeds when crossed with any pollen parent.
So you might have had more than one seed that produced a W/w plant. By chance it would have had to be crossed to another daylily that was also W/w (most likely from the same seed purchase but not necessarily). Since white seeds are almost certainly recessive it could by chance, take many generations of crosses until a W/w x W/w cross happened to produce a w/w plant and that w/w plant (which would have been a normal black seed) was used to produce new seeds.
The simplest case is that you purchased seeds that were W/w. Those would most likely have themselves produced some seeds that were W/w. At some time, by chance a cross was made in your garden of a W/w daylily with another W/w daylily. That cross produced a seedling that was w/w. The seed that produced that w/w plant would have been black. The w/w daylily when used as the pod parent will produce all white seeds from any cross. In the most likely case it would take two generations of crosses in your garden to produce white seeds. But it could take have taken many more generations since it is just by chance that a cross is made of W/w X W/w and that a w/w seedling was then used as a pod parent.