Hybridization is one of the primary means of developing new varieties of hostas. A hybrid is made by taking pollen from one hosta and placing it on the stigma of another. The resulting offspring will be a new variety, or "hybrid".
Bees and other insects are wonderful natural pollinators. In cases where hosta flowers are open-pollinated, the seedlings are usually selfed. That means that the pollen and the eggs are both from the same plant. While the offspring that are produced from selfed crosses may show a little variation, they are not actually new hybrids.
In a more controlled environment, however, intentional crosses can be made in which the plant breeder transfers pollen from one species or cultivar and places it on another of a different variety. This work is usually done with specific goals in mind. For example, a hybridizer may strive to create a new variety with a narrower leaf, a red petiole, or a larger flower. Hundreds or even thousands of crosses involving multiple generations may be required to obtain the desired characteristics.
One factor that is sometimes considered in making such crosses is ploidy. Most hostas are diploid, which means they have thirty chromosomes in each of the male and female tissues, for a total of 2n x 30 = 60. Polyploid hostas, on the other hand, contain more than two sets of chromosomes. Tetraploid hostas, for example, have four sets of chromosomes, for a total of 4n x 30 = 120. Others may be triploid (3 sets of chromosomes) or in some cases consist of a mixture of different ploidies. These are known as ploidy chimeras.
It is always interesting to compare tetraploid hostas with diploids. Tetraploids often exhibit many positive traits including better leaf substance, larger flowers, a more compact structure, shorter and stronger scapes, and brighter coloration, among other qualities.
While making successful crosses between plants of different ploidy is not possible among some genera, with the genus Hosta it is somewhat common and well-documented. Over the years, hybridizers have made crosses between tetraploids and diploids, for example, with no consideration given to ploidy status, and with no regard to which is the pod parent and which is the pollen parent. The ploidy of a given hosta species or cultivar does not appear to be a significant limiting factor when making crosses for a hybridizing program.
When two hostas of different ploidy are crossed, the ploidy status of the resulting hybrid generally falls somewhere between that of the pod parent and that of the pollen parent.
Below is a list of hybrids which have been made from crossing two hostas of different ploidy. The inferred ploidy according to flow cytometry testing by Dr. Ben Zonneveld is given, in the cases for which it is known.
'Betty' (nakiana 2-2-2 x ventricosa 4-4-4)
'Gary Jones' ('Trade Wind' 4-4-4 x 'Dorset Blue' 2-2-2)
'Green Jeans' ('Sum and Substance' 3-3-3 x yingeri 2-2-2)
'Jaz' 2.4-2.4-2.4 ('Sum and Substance' 3-3-3 x yingeri 2-2-2)
'Kiwi Black Magic' 4-4-4 (sieboldiana 2-2-2 x ventricosa 4-4-4)
'Lakeside Emerald Lights' (ventricosa 4-4-4 x 'Invincible' 2-2-2)
'Little Blue' 3-3-3 (ventricosa 4-4-4 x unknown)
'Nancy Gill 2.7-2.7-2.7 and 2.8-2.8-2.8 ('Sum and Substance' 3-3-3 x pycnophylla 2-2-2)
'Paintbrush' ('Undulata' 2-2-2 x ventricosa 'Aureomaculata' 4-4-4)
'Raleigh Remembrance' 2.5-2.5-2.5 ('Sum and Substance' 3-3-3 x plantaginea 2-2-2)
'Rippled Honey' (ventricosa 4-4-4 x plantaginea 2-2-2)
'Rosedale Barney' (ventricosa 4-4-4 x 'Invincible' 2-2-2)
'Rosedale Dough Boy' (ventricosa 4-4-4 x 'Invincible' 2-2-2)
'Rosedale Stitched in Silk' (ventricosa 4-4-4 x 'Invincible' 2-2-2)
'Slick Willie' 2-2-2 (ventricosa 4-4-4 x 'Invincible' 2-2-2)
'Stargazer' [('Beatrice' x yingeri 2-2-2) x ventricosa 'Aureomarginata' 4-4-4]
'Tardiflora Hybrida' (ventricosa 4-4-4 x 'Tardiflora' 2-2-2)
'Tossed Salad' 2.3-2.3-2.3 ('Sum and Substance' 3-3-3 x pycnophylla 2-2-2)
'Unducosa' ('Undulata' 2-2-2 x ventricosa 4-4-4)
'Venucosa' 3-3-3 (venusta 2-2-2 x ventricosa 4-4-4)
Additional Probable Inter-Ploidal Crosses:
'Alba Improved' (minor 'Alba' x ventricosa 4-4-4)
'Heartache' (ventricosa 4-4-4 x 'Gold Regal')
'Her Eyes Were Blue' ('Frosted Dimples' 4-4-4 x 'Sea Frolic')
'Holly's Honey' (ventricosa 4-4-4 x unknown, but probably diploid 1)
'Honey Hill Pins and Needles' (ventricosa 4-4-4 x longipes 2-2-2 or longissima 2-2-2)
'Misty May' ('Revolution' 4-4-4 x "seedling 43")
'Nouzang' ('Revolution' 4-4-4 x unknown)
'October Sky' ('Frosted Dimples' 4-4-4 x 'Salute')
'PeeDee Treasure' ('Gold Drop' x ventricosa 4-4-4)
'Rachael' ('Heartache' x ventricosa 4-4-4)
'Sunny Disposition' (ventricosa 4-4-4 x 'Birchwood Parky's Gold')
'Tucker Valentine' ('Herifu' x ventricosa 4-4-4)
1 'Holly's Honey' is a hybrid of ventricosa. The pollen parent is unknown. However, the pollen parent is probably diploid.
H. 'Holly's Honey' was selfed and produced 'Holly's Dazzler', which was tested by Zonneveld and found to be diploid, 2-2-2.
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