Laboratory and orchard tests have shown that the apricot (Prunus armeniaca L.) cultivars `Hargrand', `Goldrich', and `Lambertin-1' are cross-incompatible. All three cultivars are from North American breeding programs and have `Perfection' as a common ancestor. In orchard tests, compatible pollinations resulted in 19% to 74% fruit set, while incompatible pollinations resulted in <2% fruit set. Microscopic examination showed that, in incompatible pollinations, pollen tube growth was arrested in the style, most frequently in its third quarter, and that the ovary was never reached. It is proposed that self-incompatibility in apricot is of the gametophytic type, controlled by one S-locus with multiple alleles, and that these three cultivars are S1S2.
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