Diversity of Pawpaw (Asimina triloba) Cultivars in USDA Repositories and Selected Retail Nurseries c. 2022 – Richard B. Frost. J. American Pomological Society, January 2023 Number 1 p. 2.
Abstract:
This study reviewed available data for Pawpaw (Asimina triloba) cultivars in the U.S. with the goal of determining genetic diversity and genomic-morphologic relationships. Ninety cultivars available at U.S. retail sites and 20 cultivars at USDA sites (6 unique from retail) in 2022 are listed. Nine genetic studies of pawpaw are then reviewed, finding 17 genetic associations among the retail cultivars. Recent agricultural, chemical, tensile, and spectrometric morphology data are also reviewed. An association with larger fruit weight and cultivars derived
from ‘Middletown’ was found, but the remaining forms of morphology data were either uncorrelated with genomic data or otherwise unsuitable to determine genomic associations. A discussion of criteria for future genomic-morphologic studies of Asimina triloba is also included.
@Richard basing on all the date, Rebecca’s Gold is for 99% a seedling from North Carolina ? For my understanding of genetic if it would be a seed from C.Davis plants it will be near some of them (of course ‘Davis’ would be somewhere close to ‘Middletown’). Also I think that the similarity to ‘Middletown’ comes more from physical distance between original tree and ‘Ketter’. If my theory is right the line from ‘Ketter’ to ‘Fairchild No. 2’ was based on the same “Ohio” population. Also I’m mostly sure that the BEF53 and BEF54 were from selfing or full-sibling cross. Of course it’s based on my theory that admixture of BEF30 reduced the similarity to ‘Middletown’ to around ~60 %. I hope #53 or #54 is/are alive at Blandy and can be a source of some wood.
I was basing on Peterson (2003) “Pawpaw Variety Development:…” in my conclusions, I need to ask him about this matter. I mean Fig7. based on Huang (2003), as line I was thinking about ‘Ketter’ (pollinated in OH, maybe selfing) → ‘Fairchild’ → ‘Fairchild’ x op (‘Ketter’ and full siblings from 1916 contest fruit) = ‘Fairchild No.2’ → ‘Fairchild No.2’ x op (possible selfing or full sib. cross) = BEF53 and BEF54
In the time between submitting the above article and the present, I have demonstrated that markers assayed by PCR technology (e.g. SSR markers) will produce positive reactions even when the marker is not physically in the DNA of the specimen. Consequently you will have to wait for complete DNA libraries of the cultivars of interest to prove your theory.
@Phlogopite
I’ll begin with the preface that PCR assay of plant DNA (aka genetic markers) does not involve any sequencing of DNA, except for the construction of the marker. That only involves a few hundred bases per marker whereas each chromosome of the plant contains millions of bases. Instead of sequencing, horticultural PCR is based on a chemical reaction between each marker and the cell nuclei.
So about your question, we’ll first have to find out which repositories (or robust trusted sources) have the cultivars of interest. Then in the Spring or early Summer of some year we have leaf samples shipped cryogenically from the repositories to a full-service sequencing lab. This current cost is about $400 per shipment, one shipment per site.
A full-service sequencing lab will not only perform the initial sequencing and auxiliary lab work, but also assemble chromosome-level “libraries” that are needed for any comparative study. The current cost is about $5,000 per diploid specimen. For tetraploids, etc. – people who do this suffer from wishful thinking.
So once the specimens get to the lab and you pay them 50% down, the sequencing part of the work will take several months because you have to wait your turn. The actual time to prep and sequence is 3 to 8 days for plants. After that, assembling the library takes a very long time, currently about 2.5 years.
It is well known that the Asimina triloba trees #53 and #54 at the Blandy Experimental Farm are long deceased. Please provide data to support your theory that the line from "Ketter’ to ‘Fairchild 2’ was based on the same ‘Ohio’ population, and that BEF-53 and BEF54 were from selfing or full-sibling cross.
Neal wrote that ‘Fairchild’ is a seedling from the winner fruit from 1916 contest. Mrs. Ketter was an amatour grower some for my gues she grow only local (for her) seedlings. He also found that Mr. Fairchild was growing only ‘Ketter’ and his seedlings (full siblings of ‘Fairchild’). ‘Fairchild #2’ as I understand Neals graph comes from Fairchilds property. It should be the same for the other founding trees at Blandy (planted near the office), but it’s just my suppose.
Mike, Fairchild and others have documented his vast collection of plant species and cultivars at various stages of his life. I believe Peterson was aware of this. Peterson though was interested in documenting known ancestry of existing cultivars, plus a few cultivar names of historical interest. His work is very meticulous. I don’t believe further speculation is warranted.