Age of plant and ability to set seed

Hi Merk,

This is an interesting question, fertilization in plants has alot to do with ploidy or the number of chromosomes the plant has. Hibiscus are polyploids meaning they have more chromosomes than the average diploid (2n) Triploid (3n) and Tetraploid (4n). When hybridizing with polyploids, the most important thing to remember is even vs odd numbered polyploids. Even numbers can are only going to be able to pollinate other even numbered varieties and the same goes for odd numbered. The prevents problems during meiosis, where if one chromosome is left without a "partner" the egg will not be fertile and no seed will form. Unfortunately this ploidy number problem has not been worked out in hibiscus breeding, but there is alot of good information that is directly applicable on Day-lily breeding efforts. I believe that the majority of hibiscus varieties are likely one type either even or odd and poor seed setters are dubbed so because they are having the wrong ploidy pollen being used to pollinate them. I have done a few of my own breeding experiments trying to figure this out, and my preliminary data is mostly surrounding the variety "Braveheart." Charlie said he has not been able to get viable seed from this variety, so I decided to cross it only to other varieties that share a common parent with this one, as they are most likely to have compatable ploidy numbers and so far I have multiple pods forming on "Braveheart" with pollen parents that have 5th dimension (Braveheart is 5th dimension x Muffin Man). With that being said, it will not set seed when crossed with Moonstruck or Fly me to the moon.

Phew! Now going back to your question about whether or not older plants set seed better than younger plants. My answer to this question would be sometimes. It is possible that polyploid plants can forgo mitotic (cell division) events and double their chromosome number. For example if a plant originally is an odd number chromosome type say, 3n (n refers to the number of chromosomes) then if it doubles its chromosomes during mitosis, but does not divide the number of chromosomes is now 6n which would make it compatible with even type varieties. In this case a poor seed setter (because it had the wrong ploidy number) could now be fertilized by even type varieties.

In addition to ploidy number there are also several environmental factors which contribute to the sigma pads being receptive or unreceptive to pollen. Temperature and humidity seem to be the largest players here.

whoops this turned into a long post, I hope it helps!