Progenies derived from self-pollination and parent-offspring backcrosses of Echinacea purpurea (L.) Moench accession PI 631307 revealed that a sporophytic self-incompatibility (SI) system was operating in this germplasm. Offspring of progenies from the original accession were self-incompatible, but most self-pollinations resulted in some self-seed set. One seedling from such a self-pollination was reciprocally crosscompatible with its parent, proving that a sporophytic SI system was operational. The F3BC1 progeny could be classified into two offspring groups. The first group of two seedlings was reciprocally compatible with its seed parent but reciprocally incompatible with its pollen parent based on stigma collapse of the seed parent florets 2 to 4 days after pollination. The second offspring group of three seedlings was reciprocally incompatible with its seed parent but reciprocally compatible with its pollen parent. Seed set data were in agreement with classification by stigma collapse in seven of 10 backcrosses, including in several reciprocally compatible backcrosses that provided further proof of a sporophytic SI system. Additionally, a x2 test showed that the data fit a sporophytic SI model with S allele dominance operating in pollen and pistil. Assuming that S allele dominance is widespread within Echinacea purpurea, it should be possible to produce inbred lines by making successive generations of full-sib crosses.
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