Self-incompatible species require 2+ genetically distinct plants.
Well established · costly if ignored → warn
How it works
Many fruit trees carry self-incompatibility alleles at a single locus: when a pollen grain shares an allele with the pistil it lands on, the pistil rejects it and no seed sets. A plant's own pollen always shares its alleles, so it cannot fertilize itself — and neither can a second tree of the identical variety, which is genetically the same. Fertilization needs pollen from a genetically distinct plant.
What to do about it
Plant at least two, and where the species needs a second cultivar make them different varieties — two of the same will not pollinate each other.
The evidence
Evidence: confirmed against 2 sources in the research-based literature.
the 2 sources
Penn State Extension, 'Pollination Requirements for Various Fruits and Nuts', extension.psu.edu/pollination-requirements-for-various-fruits-and-nuts (read 2026-07-11): 'Apple: Cross-pollination is always needed to produce adequate fruit crop'; 'Cherry: Sweet: Most varieties are self-unfruitful'; 'Those fruits listed as self-fertile will set fruit with their own pollen.'
'Pollen-Pistil Interaction in Response to Pollination Variants in Subtropical Japanese Plum (Prunus salicina Lindl.) Varieties', PMC9692414, pmc.ncbi.nlm.nih.gov/articles/PMC9692414 (read 2026-07-11): 'Japanese plum exhibits gametophytic self-incompatibility (GSI), a prezygotic reproductive barrier where genetically related pollen is rejected by the pistil ... governed by a polymorphic locus (S) ... Self-incompatibility occurs when the same S-allele is expressed in the haploid pollen grain and the diploid pistil.'
Change history
Every change to this rule is one commit. This is what the project's version history records — the date and the reason — not a summary of it.
- self-incompatible species — fill the stub mechanism
- corpus: another rule here says what to do about a lone self-incompatible plant (remedy)
- promote to verified — self-incompatible species need 2+ distinct plants
- cite Penn State + plum GSI paper for self-incompatibility (rule confirmed)
Cite this page
Milpa Gardens. "Self-incompatible species require 2+ genetically distinct plants." Evidence grade: Well established. https://milpa.garden/rules/self-incompatible-species-require-2-genetically-distinct/
A garden-planning corpus: every claim states its evidence grade and links its sources on the page. Cite it with the grade, and add the date you read it.