Pomology Dataset & Rule Engines

02The rule engines

Ploidy and pollen sterility

Most fruit cultivars are diploid. A triploid — Bramley's Seedling, Jonagold, Blenheim Orange — carries three chromosome sets and produces effectively sterile pollen. It needs a partner, and it cannot repay one.

That is why a triploid requires two compatible diploid partners rather than one: the two diploids must pollinate the triploid and each other, because the triploid cannot pollinate either of them. A block of a triploid plus one diploid leaves the diploid without a partner, and it is the diploid that fails.

Pollen-donor status is tracked separately from ploidy, because ploidy alone does not catch every case. Male-sterile diploids exist — Magness, Waite and Ubileen among pears accept pollen freely but never donate it — and a model keyed only to ploidy would offer them as partners.

S-allele compatibility

Sweet cherry uses gametophytic self-incompatibility: each cultivar carries two S-alleles, and pollen carrying an allele the mother also carries is rejected in the style. Compatibility is therefore computed, not looked up — no shared allele gives a full cross, one shared allele a partial one, and two shared alleles a complete block.

This matters more than it sounds. For cherry a partner list is a derived output rather than stored data, so it stays correct as cultivars are added — a stored list silently goes wrong the moment the catalogue grows. The one exception is the S4′ mutation bred from the Stella line: cultivars carrying it are universal donors, accepted by every cultivar regardless of shared alleles.

Parentage, sports and named incompatible pairs

Apple and pear have no deployed genotype model to compute from, so incompatibility is asserted from published records instead, along three routes:

• Parent and offspring. A cultivar cannot be reliably pollinated by a direct parent. Jonagold is a Golden Delicious × Jonathan cross, so Golden Delicious is excluded as its partner on parentage — quite separately from Jonagold also being a triploid.
• Sports. A sport is a mutation of the same tree, genetically identical to its source and therefore useless as its partner. Tracked separately from parentage because the certainty differs: a sport shares 100% of its source's alleles, an offspring 50%.
• Named intersterile pairs. Crosses a source states outright do not work, held as explicit pairs with the reason attached.

Siblings are deliberately not excluded. Two cultivars sharing both parents inherit alleles probabilistically rather than identically, so blocking them would remove genuinely usable partners. Parent-to-offspring and sport-to-source are the only two relationships certain enough to block on.

Chill models

Winter chill is not measured on one scale, and the figures are not interchangeable. The schema records which model a figure was measured in, because a number carried across models is simply wrong:

• Hours below 7.2 °C — the simplest count, and the one most commonly quoted in nursery and extension literature. Treats every hour below the threshold as equal.
• Utah chill units — weights hours by temperature and subtracts for warm spells, which makes it better suited to climates with mild winter interruptions.
• Dynamic model chill portions — models chill accumulation as a two-step process that can be reversed before it is fixed. The most robust of the three in warm climates.

The schema supports all three. Coverage today is 17 cultivars of 285, and every one of those figures is recorded in a single model: hours-below-7.2c (17). Cold hardiness has a validated schema recording an absolute minimum survivable temperature with an empirical source, and no cultivar carries a record yet. Neither field is used to gate advice while coverage is this thin.

03How the ripening figures were obtained

A required source string turned out to be a weak guard. It is trivially satisfied by a plausible-looking citation, so it demands attribution while having no way to demand verification — and commissioned research produced authoritative-looking sources without opening them, one report saying so outright. Every ripening window therefore records the route by which its figure arrived:

transcribed0 records

Read directly from the named primary source. The only value that means somebody opened the primary document.

quoted33 records

Read from a secondary source quoting or compiling primary research, without opening the original.

converted108 records

Transcribed from a different reference frame and converted onto ours — the source stated a real observed date, measured against a different anchor cultivar or region.

reconstructed0 records

Derived from established sequence knowledge rather than read from a document.

This is not a quality ranking. A reconstructed figure drawn from a strong sequence consensus can be better than a transcribed one taken from a nursery catalogue. It is a statement about the retrieval path, so a reviewer knows which rows a spot-check would actually change.

Read plainly, 141 of 285 cultivars carry a ripening window, and none of them was read direct from a primary document — the transcribed tier is empty. The figures are converted from other reference frames or quoted from compilations. We publish that rather than round it up.

04How completely each crop is modelled

A separate axis from the one above, and a different question. Retrieval path asks how a figure was obtained; this asks whether the crop has a model at all. The distinction decides what a grower is told — a data gap invites them to look a cultivar up elsewhere, a model gap says the tool cannot answer for that crop yet.

named-pairs

No genotype model for the crop. Incompatibility comes from published parentage, sport relationships and explicitly named intersterile pairs.

Almond, Apple, Hazelnut, Peach, Pear, Pecan, Walnut

s-genotype

Compatibility is computed from published S-genotypes. Partner lists are a derived output, so they stay correct as cultivars are added.

Cherry

sparse

Partial published data. The tool can identify reliable donors within a pool but cannot rule every pairing in or out.

Apricot, Plum

05References

The dataset's backbone is the pomological literature and the national collections: the National Fruit Collection at Brogdale for accession identity and phenology, Bultitude (1983) and Morgan & Richards (2002) for cultivar description and parentage, the Brooks & Olmo Register of Fruit & Nut Varieties for release records, and peer-reviewed HortScience cultivar releases for disease resistance. Below is every named reference actually cited by a record, generated from the data rather than curated by hand.