All,
This spring I made some new observations concerning fertility of crosses between standard daffodils and species. Tetraploid standard daffodils with four chromosome sets (NNNN) crossed with diploid species for example jonquils (JJ) give an allotriploid plant with NNJ, which should be unfertile, because normal reduction division can not take place. I have found many exceptions from this rule. The plant in the picture, a cross of Trigonometry x N. cordubensis made in 2005, is pollen fertile with pollen of the constitution NJ. One half of the pollen has the dominant gene for the split corona. I pollinated in this spring Limequilla, Pink Setting and a white fertile jonquilla hybrid of my own breeding, all NNJJ, with it and shall get seedlings of the constitution NNJJ too. Many with split coronas, two to four flowers per stem and a little smaller than the seed parents, because one chromosome set J is of N. cordubensis the other J of N. jonquilla. The crosses should be fertile and some coronas coloured, if Quickstep genes are used or in the background. In 2011 crosses with Quickstep and Pink Step are planned. To get coloured crowns Actaea x N. viridiflorus and Ballygowan x N. viridiflorus (NNVV) as seed parents are further possibilities. The descendants of the type NNJV should be fertile and one half of them should have also a split corona.
Trigonometry x N. cordubensis and the described children are fertile with N. cyclamineus, N. cantabricus from Spain, N. hedraeanthus, N. triandrus and the diploid yellow bulbocodiums from Spain, as are the existing fertile jonquilla hybrids like Quickstep, Hillstar, Limequilla and some others. One half of the produced new generation has a split corona . It consists of three chromosome sets NJX or NJ(V)X, one of N with the split corona gene, one of J or J mixed up with V and one of the species listed above. I think that crosses with N. assoanus, N. gaditanus, N. scaberulus and N. calcicola should also function. Much to do and many interesting possibilities to get nice and extraordinary daffodils of quite another type than the existing. I had and have many seedlings with three different chromosome sets, but I found no plant which was fertile.
Perhaps many of you doubt my assumption that the cross in the picture has pollen of the form NJ. Most experts assume that, if the plant is fertile, the pollen should be unreduced with the same constitution as the other cells of the plant, namely NNJ. My observation for allotriploid daffodils is that this case occurs seldom. During meiosis the two N chromosome sets coorporate and divide. The J- or X chromosomes go all or most of them to one of the pollen cells. In some rare cases the residual N pollen cell is viable too. A proof of this assumption can come from the measuring of the volume of the pollen grain. The volume gives some hints for the number of the chromosome sets. The pollen grain of for example cotton or alfalfa of a tetraploid plant with two chromosome sets has twice the volume of the diploid plant with one chromosome set. For tetraploid standard daffodils the pollen grain´is nearly twice the volume of the diploid N. poeticus. If you have two or three different chromosome sets in the pollen grain you can make an addition of the different volumes. This is one way to come nearer to the solution. The other is the look at similar pollen from other plants. From Hillstar you get NJ pollen. If the pollen volume of Trigonometry x N. cordubensis is not too far from the volume of Hillstar one can conclude that both pollen are NJ. The volume of the the Trigonometry x N. cordubensis pollen is 0,0000306 cubic mm, the volume of the Hillstar polllen is 0,0000440 cubic mm and the sum of the volumes of N and J is 0,0000288 cubic mm. The volumes of the pollen grains were calculated assuming the form of an ellipsoid.
Theo