Potomac Valley Chapter
of the
American Rhododendron Society
Newsletter: Fall 2004

Calendar

• January 16, 2005 1:00 - 4:00 Regular Meeting, National Arboretum: "Special Plants and Special Places" by Don Hyatt
• March 20, 2005 1:00 - 4:00 Regular Meeting, National Arboretum
• April 27 - May 1, 2005 ARS Convention - Victoria, British Columbia
• May 7, 2005 Chapter Flower Show, National Arboretum
• May 8 - 9, 2005 Chapter Field Trip to the Roanoke area
• May 12 - 15, 2005 District 9 Meeting, Westminster, MD

The 2004 Fall Banquet

He is an avid hybridizer, and judging from the many questions from the audience I think John's enthusiasm rubbed off on everyone. We were amazed at those long leaf hybrids derived from species like R. roxieanum and makinoiR. aureum and proteoides, and giants that they have developed from R. rex and fictolacteum.

John discussed new lepidotes from Hokkaido, Japan, many of which were double forms of R. dauricum var. nanum. He showed us a very rare plant with sectored flowers like a Satsuki azalea.

He also introduced us to some of his own evergreen azalea hybrids, many of which were crosses with R. kiusianum and nakaharae. That led to a number of questions on flower color inheritance including the one below.

What's the difference between F1 and F2?

The term "F1" actually means the "first filial generation", or the initial cross between two species or distinct forms. Often an F1 cross does not yield the desired goals because some traits do not show up in those first generation seedlings.

For instance, what might one expect from a cross between an orange azalea species with a purple one? Purple color is dominant over orange in azaleas so all seedlings would likely be purple and not some ugly mix of those two shades. Every seedling does carry a gene for orange color but that trait is recessive and does not appear.

An "F2" cross is the next generation, or the result of crossing two sister seedlings from the F1 cross. Selfing an F1 plant produces an F2 also. Using the same example as before, if we crossed two of those purples from the F1 generation, the seedlings in the F2 cross often show the full range of possibilities, both purples and oranges.

Usually hybridizers want to combine the best traits from two different species when they make that initial F1 cross but don’t reach their goals till the F2. We need to know how the genes work in order to understand why that happens. Let's look at an example using both color and height.

Unlike flower color, height is not typically a simple dominant and recessive trait. It is often an average of the two growth habits. So, what should we expect if we crossed a dwarf purple species with a tall orange in the quest for a dwarf orange?

The dwarf purple would have a gene for flower color that I will show as an upper case "C" since purple is dominant. I’ll represent the gene for dwarf height with a lower case "h". The tall orange would have genes for each characteristic too, orange color represented by "c" since orange is recessive, and tall height with the gene "H".

Most normal organisms are "diploid", having two sets of genes for every characteristic. Species are often pure in their genetic makeup (also called homozygous). Thus, the dwarf purple azalea would have two genes for each trait, two for purple (CC) and two for dwarf (hh), or the genetic makeup of CChh. The tall orange species would have a similar genetic makeup, two genes for orange color and two for tall height, or ccHH.

Since every seedling gets half of its genes from each parent, all plants in the F1 generation would get and Ch from the dwarf purple and cH from the tall orange giving every seedling the same genetic makeup, CcHh. Those plants would be purple because of the dominant color factor but medium height since that trait is just an average.

F1 Generation:     ccHH x CChh = ??
x	cH
Ch	CcHh Medium Purple

In the next generation, or the F2 cross, the genes get reshuffled again so there are many possibilities. As before, half of the genes come from each parent but there are lots of choices now. The F2 results are listed in the chart below.

F2 Generation:     CcHh x CcHh = ?? (many possible combinations)
x	CH	cH	Ch	ch
CH	CCHH Tall Purple	CcHH Tall Purple	CCHh Medium Purple	CcHh Medium Purple
cH	CcHH Tall Purple	ccHH Tall Orange	CcHh Medium Purple	ccHh Medium Orange
Ch	CCHh Medium Purple	CcHh Medium Purple	CChh Dwarf Purple	Cchh Dwarf Purple
ch	CcHh Medium Purple	ccHh Medium Orange	Cchh Dwarf Purple	cchh Dwarf Orange

It turns out that three fourths of the plants will be purple. Some are pure (CC) like the original species but others carry both genes (Cc) just like the F1 parents. Only one fourth of the seedlings will have orange flowers since that happens when both recessive orange genes (cc) appear together.

We get a variety of heights now: dwarf, medium, and tall too. Approximately one sixteenth of the plants would reach our goal: orange color and dwarf height, or cchh. If we cross any two F2 plants, we would get an F3 but that gets complicated!

In reality, azalea flower color is controlled by many sets of genes so lots of unpredictable things can happen when hybridizing. The azalea cross John Weagle discussed was an F1 hybrid of a dwarf white, R. kiusianum album, and a dwarf orange, R. nakaharae. A white crossed with an orange but the F1 plants were all purple! Why?

One possible explanation for the observed outcome was that kiusianum album carries purple genes. Maybe the alba form is white because it is unable to produce pigment of any kind, possibly controlled by a recessive gene. It was basically a purple azalea but just could not produce any color. When crossed it with the orange nakaharae, the resulting F1 seedlings got those dominant purple genes from kiusianum but now the ability to produce color from the nakaharae parent. This could explain why all the F1 progeny were purple.

Now he moved to the F2 generation by crossing two F1 sister seedlings. The genes got reshuffled again. He saw purples and oranges as predicted by the prior example, but he saw a few whites too. The whites could happen if seedlings ended up with two recessive genes that inhibited color expression. However, he also got other shades like pink and red, which just means color inheritance is more complex than we imagine. If scientists ever map the full azalea genome, we might finally understand how everything works.

There is a humorous story related to the unpredictable results in inheritance. A lady once told George Bernard Shaw that he had the greatest brain in the world and she had the most beautiful body, so they ought to produce the most perfect child. He replied, "What if the child inherits my body and your brains?" He declined the offer.

“Special Plants and Special Places” by Donald W. Hyatt

Special Plants and Special Places

From our ARS District 9 Director, Don Voss

Don Voss recently returned from the Board Meeting in Hawaii. He asks that we update contact info to reflect the new ARS Executive Director:

Laura Grant, Executive Director
American Rhododendron Society
PO BOX 525
NIAGARA FALLS NY 14304-0525
(416) 424-1942

Other items in his report include:
The Copyright Committee has received minimal response to its request for authors and photographers to supply (or deny) permission to reproduce their work for Internet publication. Please cooperate, using the form from the JARS or a typed copy and spare the committee the cost and tedious effort of tracking you down individually.

Bob Weissman has devoted an amazing amount of work to the Society’s website. Over 900 high-quality images of hybrid and species rhododendrons are available to you. Click on “Plant Data” in the header and proceed with selection. This site is a treasure—visit it!

The R & A News (click Rhododendron and Azalea News on the rhododendron.org home page) wants contributions from members. Some topics desired are book reviews, ideas for chapter activities, reports on garden visits, and plant tips.

Bill Mangels’ Endowment Fund Committee has continued its yeoman service, researching questions related to the Society’s Endowment Fund. The committee presented options relating to fund accounting and investment practices, including an option that would place these funds under a separate ARS foundation. The Bylaws and Policies Committee recommended that the Donor Restricted Account (Publications) be merged into the Donor Restricted Account (General), citing reasons that were commented upon negatively by the District 9 Director. On a motion by the Western VP, the present fund structure and accounting and investment arrangements were reaffirmed without change. Given the present sizes of the two donor-restricted accounts, I believe that at this time the interests of the Society are best served by directing endowment donations to the Donor Restricted Account (General). Donations to the General Fund and Research Foundation are, of course, always welcome.

Other Notes:

The December newsletter will carry our seed exchange. If you have any seed to donate, please send it to Don Hyatt by mid November.

Convention 2006 plans are proceeding well. We had nearly 30 people come out for the "potting party" at Marshy Point Nursery on 10/23/04. Join us next time. We had lots of fun!