Dihaploidy yields diploid apomicts and parthenogens in Erigeron (Asteraceae)

 Premise of the study: Dihaploids result when tetraploids produce reduced eggs that develop without fertilization into diploid progeny. This process is useful for reducing genome complexity and studying trait expression at different ploidal levels. In this study we evaluated genetic inheritance and expression of diplospory ( D ) and parthenogenesis ( P ) in a population of dihaploids produced by tetraploid apomictic Erigeron .  Methods: From 400 mostly maternal (tetraploid) progeny, we identifi ed 64 (16%) dihaploids with 2n = 18 (53 plants) or 2n = 19 (11 plants). Differential interference contrast (DIC) imaging of ovules was used to evaluate megasporogenesis (meiosis vs. diplospory) and capacity for parthenogenetic embryo development. Seed production was estimated as the proportion of fi seeds.  Key results: For 60 analyzed dihaploids, diplospory vs. meiosis segregated approximately 1: 1 ( P = 0.44) while all exhibited parthenogenetic embryo development. Parthenogenesis for meiotic progeny ( n = 27) was observed in approximately 50% of ovules. Apomictic dihaploids (combining D and P ; n = 33) produced seeds with mean 24.8% (range 1.3–74.4%) of total fl owers.  Conclusions: The dihaploid population consisted of half apomicts ( D + P ) and half parthenogens ( P only). We infer that formation of dihaploid seeds requires the parthenogenesis locus. The highest seed values obtained for diploid apomicts are comparable to those recorded for wild type polyploid apomicts. This is one of the fi rst reports of diploid apomixis in the Asteraceae and it demonstrates that both diplospory and parthenogenesis can be transmitted and expressed at a high level in the diploid condition.