Dominance in Sinningia Heredity

By examining hybrids between species with contrasting traits, one can get an idea of the genetics of some of these traits.  For instance, indeterminate growth (an indefinitely extending stem) appears to be very dominant, in that only a little bit of indeterminate-growth ancestry is sufficient to make the hybrid have the same trait.  On the other hand, possession of peduncles (see below for definition) usually - but not always - dominates.

As for other traits, the evidence suggests that galeas are recessive, while tubers are dominant.  Such features are almost certainly controlled by more than one gene, so "dominance" will not always be a yes/no proposition.

1. Dominance of indeterminate growth
2. List of indeterminate x determinate hybrids
3. Partial dominance of peduncles
4. List of pedunculate x nonpedunculate hybrids
5. Galeas are more or less recessive
6. List of hybrids involving galeate sinningias
7. Tubers are dominant?
8. List of hybrids between tuberous and nontuberous parents

Dominance of Indeterminate Growth

Some sinningias have determinate growth: that is, a flowering-size plant makes only a fixed number of leaves and then flowers.  Other sinningias have indeterminate growth: the plant makes nodes and leaves without a predetermined limit on their number.  The majority of sinningia (and almost all other gesneriads) show this growth pattern.

Even the determinate species of sinningia usually have indeterminate growth until they reach flowering size.  Examples are S. leucotricha and S. defoliata.

So the question arises: when a determinate plant is crossed with an indeterminate plant, what type of growth does the resulting hybrid exhibit?

In all cases that I know of, the answer is that the hybrid has indeterminate growth.  In other words, indeterminate growth is dominant and determinate growth is recessive.  A plant with one indeterminate parent and one determinate parent will ignore its determinate ancestry and show regular indeterminate growth.

This is even true in one case where the indeterminate parent was itself an indeterminate/determinate hybrid and thus probably harbors one or more silent determinate genes.  In the list of examples below, one of the indeterminate parents was S. 'Peninsula Belle', a cross between S. reitzii (indeterminate) and S. lineata (determinate).  If the determinate/indeterminate trait were controlled by a single gene, we would expect that half of the plants resulting from a cross between S. 'Peninsula Belle' and a determinate plant would show indeterminate growth.  Such is not the case, however.  So far, all the progeny exhibit indeterminate growth, like the S. reitzii grandparent.

This suggests that the determinate/indeterminate trait is controlled by more than one gene.  It also suggests that it will be difficult to create determinate hybrids unless only determinate parents are used.  For instance, it may take several generations of crosses to recover a determinate hybrid from S. reitzii x leucotricha.  Where the hybrids are likely to be sterile (as appears to be the case with those of S. helioana and perhaps S. defoliata as well), it may be impossible to get the unique growth pattern of the determinate parent without using a determinate plant as the other parent.

Hybrid List

Here is a list of some hybrids (mostly my own) that have one determinate parent and one indeterminate parent.  Only hybrids that have bloomed are included.  The results show that all the hybrid offspring have indeterminate growth.

Hybrids between two determinate parents have always yielded determinate plants.  Examples:

• S. leucotricha x douglasii
• S. leucotricha x piresiana (Jon Lindstrom's hybrid)

Partial Dominance of Peduncles

Some sinningias have pedunculate inflorescences.  That is, when there are multiple flowers per axil, they are borne on stalks which carry more than one flower.  A complete discussion of peduncles can be found here.

Some species with peduncles are S. lineata, S. reitzii, and S. aghensis.  Some species without peduncles are S. leucotricha, S. piresiana, and S. insularis.

Hybrid List

Here is a list of some hybrids that have one pedunculate parent and one nonpedunculate parent.  Only hybrids that have bloomed are included.  The results show that most of the hybrid offspring have pedunculate growth.

Galeas are Recessive (Mostly)

Some sinningia flowers have galeas.  The upper two lobes of the corolla extend about 1 cm farther out than the lower three lobes, which are shortened.

The largest galeas are borne by a closely related group of species in the Dircaea clade.  A few species in the Corytholoma clade have an apparent galea, but the lower three lobes are not shortened but rather curled back so that the upper lobes project.  Examples are S. araneosa and S. defoliata.

Hybrid List

Here is a list of some hybrids involving galeate species.  What evidence there is strongly suggests that galeas are recessive.  That is, a cross between a galeate species and a nongaleate species will result in nongaleate plants.  (Crosses between hybrids are another matter.)

Tubers are dominant?

A few crosses have been done between tuberous sinningias and non-tuberous paliavanas or vanhoutteas.  I believe the resulting hybrid plants have all had tubers.

I have only one of them, Jon Lindstrom's Sinningia conspicua x Paliavana tenuiflora.  This one definitely has a tuber.

Hybrid List

This is the nucleus of what I hope will be a much longer list of hybrids between tuberous and non-tuberous parents.  If you have them, send me your results!  (See here for the email address.)