Self-incompatibility, seed abortion and clonality in the breeding systems of several Western Australian Drosera species (Droseraceae)

Western Australian Drosera L. species include one annual and many tuberous and pygmy perennials. In 20 species or subspecies, 17 taxa were self-incompatible (SI) and three were self-compatible (SC), as assessed by patterns of seed set and pollen tube growth. All SI species were clonal (tubers or gemmae), but two SC species were clonal (gemmae) and one was annual. Self-pollen tube inhibition confirmed that SI species were pre-zygotically self-sterile. The sites of SI pollen tube inhibition varied from early (stigmatic) to fate (stylar, placental, ovular), which suggests continuing evolution in the expression of the SI response. Self-compatible species showed little inbreeding depression, but SI species showed considerable inbreeding depression as measured by seed abortion. In the three species tested, open-pollinated capsules were typically more fecund than hand-pollinated capsules. In D. glanduligera Lehm., this might represent position effects in an inflorescence that were reflected in the sampling method. In other species, however, this might also reflect biparental inbreeding depression in the glasshouse plants. Interspecific crosses between D. tubaestylis N.Marchant & A.Lowrie (n = 14) and D. rosulata Lehm. (n = 13) were slightly successful, with no pollen-pistil incompatibility interaction, but with extensive seed abortion. This is the first report of SI in Droseraceae.