Single Gene Control of Postzygotic Self-Incompatibility in Poke Milkweed, Asclepias exaltata L.

Single Gene Control of Postzygotic Self-Incompatibility in Poke Milkweed, Asclepias exaltata L.

Sara R. Lipow^a and Robert Wyatt^b
^a Department of Botany, University of Georgia, Athens, Georgia 30602
^b Institute of Ecology, University of Georgia, Athens, Georgia 30602

Corresponding author: Sara R. Lipow, Department of Forest Science, University of Oregon, Corvallis, OR 97331-5752., sara.lipow{at}orst.edu (E-mail)

Communicating editor: M. K. UYENOYAMA

Most individuals of Asclepias exaltata are self-sterile, butall plants lack prezygotic barriers to self-fertilization. Todetermine whether postzygotic rejection of self-fertilized ovulesis due to late-acting self-incompatibility or to extreme, earlyacting inbreeding depression, we performed three diallel crossesamong self-sterile plants related as full-sibs. The full-sibssegregated into four compatibility classes, suggesting thatlate acting self-incompatibility is controlled by a single gene(S-locus). Crosses between plants sharing one or both allelesat the S-locus are incompatible. An additional diallel crosswas done among full-sib progeny from a cross of a self-sterileand a self-fertile plant. These progeny grouped into two compatibilityclasses, and plants within classes displayed varying levelsof self-fertility. This suggests that the occasional self-fertilitydocumented in natural pollinations is caused by pseudo-self-fertilityalleles that alter the functioning of the S-locus.

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