JARS v45n2 - Finding Big Breeders

Finding Big Breeders
Mark Konrad, MD
Sewickley, Pennsylvania

Sometimes a casual observation will save time and energy in a hybridizing program. For instance, some rhododendrons such as 'Calsap' open pollinate every truss completely, while others such as 'Mist Maiden' open pollinate incompletely. This observation might lead us to deduce that the one will lend itself quite readily to crossing whereas the other might be resistant.

R. 'Mist Maiden'
'Mist Maiden'
Photo by Mark Konrad

Since there can be many causes for rhododendrons to open pollinate or not, we cannot speak in scientific absolutes, especially in view of the complexity of the process. Factors that cause pollination to fail include genetic incompatibility, plant sterility, improper techniques, unfavorable weather conditions, improper timing, faulty reproductive parts and deteriorated pollen.

R. 'Calsap'
Photo by Mark Konrad

Despite these factors, observing which plants readily open pollinate or not might serve as an index to eliminate some of the unproductive aspects of hybridizing or at least show where extra effort must be concentrated. It would also be well to identify the appreciable number of rhododendrons that exhibit selfing incompatibility.

R. maximum
R. maximum
Photo by Mark Konrad

Pollen fertility is another matter and requires a totally different analysis. As an example, I found 'Mist Maiden' pollen crossed very well on 'LaBar's White' this year.
I may have overlooked other factors that cause heavy open pollination. One example that comes immediately to mind is R. maximum which usually totally open pollinates; however, there is the possibility of apomixis taking place. [Apomixis is an uncommon reproductive process where seed is produced without fertilization, ed.]
Nevertheless, observing which rhododendrons tend to open pollinate easily should show us desirable plants to use in hybridizing programs.

Dr. Konrad shares his insights, based on many years of experience in rhododendron hybridizing and culture, with ARS Journal readers from time to time.