P. ‘Damsel’s Delight’ (foot), P. ‘Betty Myles Young’ (centre) and the common Passion flower (top ).

Passiflora Passion flowers – Polyploids

In nature plants commonly have multiple occurences of chromosomes, called polyploidy. A single set is called haploid, a double diploid, a triple triploid & four sets tetraploid. Some plants like many commercially grown strawberries have as many as eight sets, which is called octoploid. Tetraploids of other plants have occured as a spontaneous mutation naturally in the wild. There are some wild Passiflora tetraploids but they are rare. Polyploidy is of interest to hybridizers as it can give rise to larger flowers, fruit & leaf differences and more vigorous and hardy plants. See the Riverside® Hybrids.

Variations

Passiflora like ourselves are diploid, meaning that they have 2 copies of each chromosome. For most Passiflora, but not all, 2n (the number of chromosomes) =18, so their pollen or egg cells are half that, n=9. Tetraploid plants have 4n=36 chromosomes & their pollen usually 2n=18.

Polyploid Passiflora

Thanks to Dr. Knight (USDA) we have a tetraploid hybrid, P. ‘Byron Beauty’. More recently Dr. Roland Fischer has also created tetraploid species selections such as P. ‘Clear Sky’ & P. ‘Emil Kugler’  which are both selections of P. caerulea and also some spectacular tetraploid hybrids such as P. ‘Jara’ & P. ‘Inspiration’.  I have also managed some polyploid hybrids myself with plenty more to come I hope!

Sometimes not all the tissues in a plant will have the same increase in chromosomes, which can cause some oddities e.g runners reverting back to diploid from tetraploid. The first triploids are also now starting to appear.

Dr Roland Fischer

Roland comments:-

”Hybrids often produce unreduced egg cells (2n=18) which would give 4n=36 seeds with pollen from tetraploids, that means they would be true tetraploids.”

This means that a number of diploid hybrids, including ones previously thought sterile may be able to cross with tetraploids. It is also likely that some hybrids and species will produce a small number of unreduced pollen grains which could be used to set fruit on tetraploids to produce fruit containing tetraploid seed. Dr Roland Fischer, Dr. Les King, others and myself are doing work on this – see papers below.

The Passiflora Cultivar Registrar Dr Les King on the left & myself studying one of my new Passiflora hybrids – a very unusual polyploid cross.

Publications

‘Pure Passion’ PLANTSPROFILE on Myles Irvine by Philip Clayton
The Garden (RHS) Volume 135 Part 9 September 2010
The Garden September 2010 PDF

‘Breeding hardy Passiflora’ by Myles Irvine
The Plantsman (RHS) New Series Volume 9 Part 3 September 2010 The Plantsman 2010 PDF 

Investigation of Passiflora hybrids using flow cytometry by L.A. King and M.S. Irvine
Passiflora (2010), 20(1): pp. 5-1 Passiflora polyploids PDF