My experience with Rosa banksia hybrids began in the year 2000 with the chance creation of a repeat blooming fertile hybrid shrub given the name, 'Lila Banks'. Parentage is 'Lilac Charm' x (R. banksiae banksiae x 'Old Blush'. Details of the development of this seedling were detailed in my last article entitled, "Banksia Hybrids, A New Beginning".

At the time of my first article I was unsure about the fertility offered by this new hybrid. As of this writing, it is apparent that 'Lila Banks' is fertile as pollen parent with many modern hybrids. Experiments performed in the last year creating hybrid seedlings with a number of seed parents bear this out. Banksia roses have long resisted attempts at hybridization. Although hybrids have been created in the past, many are infertile or difficult to propagate and many are now lost to commerce and likely extinct. These new fertile offspring offer hybridizers an unexplored direction in which to exploit the many desirable characteristics offered by this species.

Banksia roses are known throughout the temperate zones of the world for their great vigor, long life, floriferous and prickle free nature. They are generally resistant to most insects and diseases. They exhibit unusual elongated leaflets and blossom in huge displays.

Much hybridization has been done to further development of roses for cool climates. Relatively little has been done to improve and expand the types of roses that prosper in temperate climates. This is largely the role these new hybrid cultivars are expected exploit.

Newest Hybrids

Several goals were kept in mind while selecting seed parents to use with 'Lila Banks' pollen. Requirements include reliable germination, vigor, Winter flowering, an evergreen nature, repeat bloom, ease of rooting and disease resistance.

The first seed parent chosen, 'Antoine Rivoire', is a very early Hybrid tea and derives largely from Rosa gigantea. It produces many fertile seed in my climate. As progenitor of 'Ophelia' it has much to offer those seeking to breed roses adapted to mild climates with hybrid tea form. The resultant seedling, 'Riverbanks' exhibits good repeat, tea fragrance and sets hips easily. The seed of this cultivar is large and easy to handle. Seedlings are relatively healthy. The percentage of germination is generally good.

'Riverbanks' is fertile throughout a wider range of temperatures than is typical with many cultivars. Under warm conditions flower size and petal count will be reduced but fertility will often be retained.

A number of open pollinated hips were produced in 2005 using 'Riverbanks. In order to test fertility, seed from these hips was germinated early in 2006. Many seedlings were produced. I am selecting those exhibiting the best vigor while preserving the characteristics I would like to preserve like elongated leaflets and desirable flower form. Several are being evaluated at this time for use in backcrosses.

Another parent selected was the Shrub Rose, 'Armada'. This cultivar is bred from two well known roses, 'New Dawn' x 'Silver Jubilee'. The use of this rose as seed parent is to instill hardiness, modern form, disease resistance and ease of rooting. 'New Dawn' derives largely from Rosa wichurana.

Many seedlings of this cross were germinated in 2006. Of those, several are being evaluated. The general tendency is toward pink semi-double blossoms of small to medium size. Some of these seedlings are showing a tendency toward a vigorous habit and may be shrubs or climbers. It is too early to tell whether any of these seedlings will offer commercial potential.

The Hybrid Tea, 'Sweet Afton' is a rose I admire. It sets seed easily here and offers long stems, long buds and strong fragrance. It has a strong rosa foetida heritage which offers the possibility for yellow in seedlings, parentage, ('Charlotte Armstrong x 'Signora') X ('Alice Stern' x 'Ondine')

Since Rosa banksiae banksiae produces its blossoms on quite short stems as does 'Lila Banks', I was unsure what to expect from this cross. So far stem length seems to be varied and intermediate in length among offspring but hybrid tea flower form is evident in most seedlings.

One of the seedlings from this cross, 'Sweet Afton' x 'Lila Banks' #3 is light yellow in color and offers an interesting flower form similar to that of a Water Lily. I will be working to bring more yellow into the genetic mix in the near future.

Hybrids of 'Sweet Afton' x 'Lila Banks' show promise for producing other crosses of the same type. Large quantities of seedlings need to be produced in order to select out those with the most desirable traits.

One last hybrid of 'Dortmund' x 'Lila Banks' was produced. 'Dortmund' is tetraploid Rose kordesii hybrid descended from 'Max Graf', a hybrid of Rosa rugosa x Rosa wichurana. It is very disease resistant and tolerant of cold temperatures. The one surviving seedling lacks vigor but proves the fertility of the cross. Only one hip was pollinated last season. Other attempts should be made to get a better idea of the range of types this cross can produce. Blossoms are semi-double and red.

Most of these seedlings produce the odd elongated leaflet or elongated sepal indicating their affinity to R. banksiae banksiae.

Fertility

Often crosses between diploid species like Rosa banksia banksiae and modern tetraploid garden roses result in infertile triploid mules useless to breeders. Occasionally these normally infertile triploid roses offer fertility, a new pathway for rose breeders to continue a new line of breeding. Now roses of most types can now be utilized for hybridization.

Both 'Lila Banks' and 'Riverbanks' were confirmed triploid by Researcher David Zlesak. The "Root Tip Squash Method" was used to determine ploidy. The "Root Tip Squash Method" involves removing the actively growing root tip of the cultivar in question. It is then stained pressed between slides and examined using a Light Microscope to determine chromosome number.

David Zlesak offers some clues as to what is happening with these hybrids on a genetic level as he observes;

"If trends that I've noticed in general hold true both Lila Banks and River Banks should produce primarily tetraploid offspring with tetraploid parents based on their pollen diameter. Pollen size is determined, in part, by chromosome number and is useful to predict ploidy. There may be some triploids as well (if the gamete from the triploid has one set of chromosomes) or even pentaploids. The mean pollen diameters of these two triploid roses are about that expected for tetraploids (although the standard deviation and variability around the mean is generally greater)."

"The diameter of 30 pollen grains (in micrometers) per rose were recorded and below is are the means and standard deviations of each. There was a high rate of pollen abortion in 'Lila Banks' (~50%) and more variation in size (larger standard deviation) suggesting that out of the stained grains there may also be a lot of aneuploids (extra/missing chromosomes) which can lead to reduced viabilty and fitness of such pollen and the resulting offspring as well. 'River Banks', however, relatively speaking had less aborted pollen (~30%) and much more uniformity among pollen grains. The diameter across pollen grains had greater consistency, like what is generally found from fertile tetraploid roses."

"In general the pollen diameter of roses with 1x (7 chromosomes) pollen (standard pollen from diploids) is ~31-35 micrometers, 2x pollen (standard from tetraploids) ~35-44 micrometers, 3x pollen ~45-50 micrometers, 4x pollen ~48-52 micrometers. The larger pollen grains in 'Lila Banks' may reflect some 3x pollen through unreduced (2n) gametes as well as aneuploids with higher chromosome numbers."

'Lila Banks'

43.1 (Average pollen size) 4.1 ( Standard deviation)

'Riverbanks'

40.2 (Average pollen size) 3.7 (Standard deviation)

My experiences bear out David's findings. Greater than average pollen size explains diminished fertility with use of 'Lila Banks' pollen as observed with most, but not all diploids. Most pollen is too large to provide fertility with these roses.

I have noted that 'Lila Banks' seems to be much more fertile with tetraploids. 'Riverbanks' is more fertile with tetraploids but also accepts most diploid pollen allowing for potential fertility with a wide number of rose species. 'Riverbanks' produces pollen seemingly fertile with most garden roses, though seedlings have yet to be germinated to bear this out.

Fertility of 'Lila Banks' is observed with most tetraploids, though as predicted some seedlings exhibit diminished vigor because of possible aneuploidy (abnormal chromosome count). However, in my experience some seedlings of diminished vigor are to be expected with any cross.

Because of the large size of pollen produced by 'Lila Banks', adaptability for use with pentaploids, or even hexaploids might be possible. This would lead to some very unusual hybrids with hybrids of Northern rose species including those of the section caninae offering much greater climatic adaptability than I would have expected from hybrids of R. banksiae banksiae. This would be a very interesting line of breeding to carry out experimentation with and might greatly expand the climactic tolerance these hybrids are capable of attaining.

Present and Future Crosses

As of this date few of these seedlings seem to offer much in the way of commercial potential but are instead steps on the path to better hybrids. A few may be made available to those seeking to further this line of breeding.

Crosses in 2006 focused on incorporating modern R. bracteata and R. clinophylla hybrids. Good seed set was generally obtained using 'Riverbanks' as seed parent. Propagation and utilization of 'Riverbanks' and other newer hybrids for use in reciprocal and backcrosses will be a focus of the 2007 hybridizing season.

Other goals will be the utilization of modern yellow pollen parents and the incorporation of Noisettes to produce repeat blooming climbers.

Further testing and cross breeding will be attempted in order to broaden the range of plant forms, blossom types and colors.