Blotch Heat Stability

As mentioned in a previous post (The Hulthemia Holy Grail - Blotch Heat Stability), the heat stability of the Hulthemia blotch is one of the biggest challenges in breeding for this group of rose hybrids.  The Hulthemia shown below was a brand new seedling in 2011 and got my attention when it first bloomed.  I made a post (A Most Remarkable Blotch) about this seedling last year.  This year it appears to have excellent blotch heat stability given the fact that last week on the 2 days prior to this bloom opening, the temperature was 102º F and 108º F, and then 102º F again on the day this photo was taken.  Like many of the other Hulthemias with improved blotches, this one doesn't seem to release any pollen.

Mixed Hulthemia Pollen - A Good Recipe!

Having produced many thousands of rose seedlings (unique roses resulting from planting rose seeds), I have tried to keep as complete records as possible, in order to trace the heritage of my seedlings.  Data on the pollen and seed parents, along with some other information are kept in MS Excel spreadsheets.  This allows me to trace a seedling's pedigree.  These kind of pedigrees are helpful when crossing various roses with one another if you have a particular objective in mind.

Not long after I started breeding Hulthemia roses, I observed that many cross pollinations failed to produce rose hips (hips are the fruit within which rose seeds develop).  Presumably this meant that the pollen or seed parent was of lower fertility or that there was some other incompatibility.  This made for a lot of work without much to show for it.  Realizing that when breeding for Hulthemias, it was the blotch trait that I was trying to capture, and was really not concerned with the heritage (just as long as one of the parents exhibited the blotch), I decided to mix the pollens of the best Hulthemias with each other and use the mixed pollen for cross pollinations.  This has allowed for a much better hip "take" (the hips stay on the plant to develop seeds) and a larger number of seedlings from which to select for use in further breeding. I think that this approach has allowed us to make quicker improvements in the Hulthemias by shortening the generation time.

Since each year we have been seeing progress in Hulthemia blotch development (blotch size, blotch intensity, and heat stability of the blotch), I have been using the mixed pollen of the newest (current year seedlings) that exhibit the best blotches.  I especially like doing this later in the breeding season (like now), in order to take advantage of those new seedlings that are exhibiting the best blotch heat stability.  Last year I posted more about how Hulthemias tend to lose their blotches in the heat in the post entitled The Hulthemia Holy Grail - Blotch Heat Stability.

Below is shown the pollen cup that I have been using to collect the pollen of the newest batch of Hulthemias that are showing the best blotches, even in our heat.  I have been applying this pollen to some of the best Hulthemia seed parents, as well as to non-Hulthemia parents, including 'Darlow's Engima', 'Sunny Knock Out', 'Francis Meilland', and some of my own non-Hulthemia seedlings.

Each day fresh pollen is collected from the best new 2012 Hulthemia seedlings.  The petals seen in the photos below represent 3 batches of Hulthemias that contributed their pollen for the cross pollination effort this year.  These are some of the best Hulthemias that I have seen and represent improvements over prior years.

Hulthemia Fertility - Update on Seedling "O352"

If you are familiar with the Hulthemias, it is easy to see why I wanted to use "O352" in further breeding:  It has one of the largest blotches that I have ever seen; the blotch is heat stabile (doesn't fade in the summer like most Hulthemias); it is fully remontant (blooms all summer); it doesn't get any powdery mildew; and, unlike the often vicious armor (thorns) seen with most Hulthemias, this one appears to be completely thornless (even the rachis are prickle free).
Note "O352" was mentioned in an earlier post The Largest Blotch A Dead End?

Time and time again, however, I had tried to get pollen from this particular seedling to use in breeding, but to no avail.  There was just no pollen released.  It is sterile as a pollen parent.

So, what do you do when you have a rose/Hulthemia that is pollen sterile?

Well, one of the wonderful things about roses is that they can be used as either a pollen parent (male parent), or a seed parent (female parent).  The very first Rose-Hulthemia hybrid that proved to be fertile was 'Tigris' (a once bloomer and a fairly weedy type plant),  but it too was pollen sterile.  It only worked as a seed parent.  Fortunately for all of us, when pollen was applied to 'Tigris' blooms, hips formed, yielding viable seeds. All of the new Hulthemia hybrids get their characteristic darker central blotch from 'Tigris'.

In the photo below, you can see some pollen spilling onto the petals of "O352".  Knowing that it does not produce pollen, you have probably guessed that I played the bee in this case, slopping pollen onto the stigmas.  You will notice too, that tags were hung from the peduncles, identifying the pollen parent(s).

In the second photo below, you can see that like 'Tigris', "O352" appears to be fertile as a seed parent.  Right now, there are many hips devoloping on it.  I am hopeful that the seeds forming within the hips will germinate when they are planted this coming winter.

You may be able to make out the writing on the tag as "Rx".  I use the "Rx" designation to indicate Radler genetics (Bill Radler is the breeder of the Knock Out series of roses known for their strong resistance to many of the fungal diseases that attack roses).  Rather than make many different crosses using the various pollens that I have from the Bill Radler group ('Knock Out', 'Double Knock Out', 'White Out', 'Sunny Knock Out', 'Carefree Sunshine', and 'Milwaukee's Calatrava'), I mix the pollen.  For me, the crucial thing is bringing in the genetics of cleanliness from these roses, rather than knowing the specific pollen parent.  "Rx" seemed to me to be a good description too, since Radler genetics are the right prescription for better health in roses (and Hulthemias)!