H: Friday, June 10, 2011

Creel Demonstrates Rule #4

In June 2007 Mike Creel wrote the following:

"I well-pollinated two different Mountain Flame Azaleas - 'Gamecock' and 'Walhalla Gold' - with fresh pollen from a nearby eastmanii this May, and NONE of the flowers formed a seed pod, acting like they had never been pollinated."

"Can anyone try to explain this apparent incompatibility between calendulaceum and eastmanii?"

"A friend of mine in Oregon has had several successes with crossing occidentale and eastmanii, so those species appear compatible."

Answer to the Question.

The Mountain Flame Azalea, Rhododendron calendulaceum, is a tetraploid and a member of the tetraploid clade of deciduous azaleas.

Rhododendron eastmanii and Rhododendron occidentale are diploids and members of the diploid clade of deciduous azaleas.

By Rule #2, Rhododendron occidentale will accept pollen from Rhododendron eastmanii.

Rule #2: Species within a given clade freely cross in both directions. The resulting offspring are normally viable and fertile. The offspring normally reflect characteristics that are intermediate between the 2 species involved.

By Rule #4, Rhododendron calendulaceum will reject pollen from Rhododendron eastmanii.

Rule #4: Species in the tetraploid clade normally reject pollen from species of the diploid clade. Exceptions occur but they are extremely rare.

By Rule #3, Rhododendron eastmanii would accept pollen from Rhododendron calendulaceum.

Rule #3: Species in the diploid clade freely accepts pollen from species in the tetraploid clade. The resulting offspring are often viable but usually sterile (bloom but do not produce seed) triploids. The offspring often reflect more characteristics of the tetraploid pollen parent. Offspring having pink or salmon colored flowers with a yellow blotch are not unusual. Deformed anthers, multiple petals and color streaks in the corolla are also frequently seen.

Read Rules of Engagement.

John and Sally Perkins
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