Genetic and physiological mechanisms of self-incompatibility deficiency and evolutionary backgrounds in establishment of self-compatible strains in Lilium longiflorum

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Lilium longiflorum, bulbous species of Liliaceae, is endemic to islands of the Ryukyu Archipelago and to the eastern seacoasts and satellite islands of the mainland of Taiwan. The species has long been regarded as self-incompatible, but we previously revealed that natural populations of L.longiflorum in Kikaijima Island, located in the northern part of the Ryukyu Archipelago, were dominated by self-compatible individuals. In this study, pollen tube elongation and seed set after artificial self-pollination, flower morphology and phylogenic relationships based on AFLP were investigated to clarify genetic, physiological and biogeographical features of shift from self-incompatibility to -compatibility using individuals established from seeds collected in 18 natural populations covering the entire species distribution. The important results obtained were as follows :1)Self-compatible individuals were dominant in northern islands and southernmost island in the species distribution.2)Self-incompatible reaction emerged not qualitatively but quantitatively, and not only in a style but also in aovary.3)Self-compatibility inhereted dominantly in F_1 progeny.4)Reduction in amount of pollen production in northern self-compatible populations indicated that selfing is dominant in these populations.5)Phylogenic tree based on AFLP showed that shift from self-incompatible to compatible dominant population in the species occurred parapatrically in the northern and southern parts of the species distribution.6)Self-compatible L.longiflorum strains of the southernmost populations in Lanyu Island ecologically very similar to genetically the closest species, L.formosanum.