Iiya, good point. Polyembryonic seed made it possible to transfer clones of great tasting citrus around the world when travel was slow and difficult. Citrus that were known to breed true to type, would be the preferred ones to start new groves from. It could hardly be more convenient for the orchardist and the best available material has been selected to be polyembryonic via this convenience. So taste may not be associated with polyembryony at all.
Thank you and all the people on this forum for sharing so much knowledge. Its a lot to think through when hoping for a few pleasant tasting citrus to grow in zone 8a. The long term F1 breeding project started by Walt is especially interesting. You posted a link there, discussing the inheritance of sour vs sweet in citrus and also the information about the precocious poncirus not producing perfect flowers for several years. Not to say the pollen would not be useful. I had a lemon that behaved this way and was about to discard it last spring but it suddenly starting producing perfect flowers and so I saved it and got lemons. (as in fruit not bad results) The idea of developing a deciduous citrus from PT genes seems like the ideal solution to cold hardiness. Such complicated genetics to work through. But a really good solution. I take to heart comments that after many years of breeding the results are still not satisfactory. I hope all the work from the breeding projects done by the forum members does not get lost. It seems that the cold hardy plants developed before 1930 are still the starting material for many cold hardy citrus breeders. There must have been intrepid gardeners between 1930 and 2000 breeding better cold-hardy citrus. But who know what happened to them?
This is a follow on question about polyembryony, I made crosses last year using changsha as the citrus mother with citromelo, tanglelo, meyer lemon, and key lime as pollen. The majority of the flowers pollinated with citromelo and tangelo proceeded to fruit, and produced about 30 seed per fruit which is normal for this changsha. The lemon on the other hand produced far fewer seed, around 7-8 per fruit and far fewer fruit actually took. The lime was the worst. Out of about 15 fruit, two set. One was completely seedless and the fruit very small the other contained only one large seed.
This winter when the seed were planted, the tangelo cross sprang up first and grew vigorously, the citromelo also followed and grew fairly fast. The lemon seedling came up very slowly and are growing slowly. Some creature broke into the green house, and chewed the lime seed to mush. I estimate the actual number of zygotic seedling to be low (10-15%) based on the small number of plants with PT leaves among the citromelo seedlings. The thing that makes me wonder is that the number of plants germinating from each seed seemed to be affected by the pollen parent. The changsha x lemon crosses were all mono-embryonic except for one seed which has two seedlings. They came up as large seedlings but are growing very slow and a few seem to lack a meristematic buds. They put out three leaves and stop though the leaves get bigger. The difference in germination and growth could have been the soil, I used two batches of potting soil but the difference in number of seedlings per seed between the lemon and tangelo is odd. I would be glad to hear your thoughts on whether the pollen parent can effect the number of embryo's per seed or if this is just a coincidence.