Euphytica 86: 15-23, 1995. 15 (~) !995 KluwerAcademicPublishers. Printedin the Netherlands. Early postfertilization ovule culture in Alstroemeria L. and barriers to interspecific hybridization M.J. De Jeu & E. Jacobsen Department of Plant Breeding, Wageningen Agricultural University (WAU), P.O. Box 386, 6700 AJ Wageningen, The Netherlands Received28 February 1994;accepted 18 May 1995 Key words: Alstroemeria, Alstroemeria, Inca Lily, embryo histology, interspecific hybridization, incongruity, pollen tube growth, ovule culture Summary An early postfertilization ovule culture technique in Alstroemeria was described in which young ovules were cultured in vitro two days after pollination. This resulted in the direct production of seedlings in a normally incongruous cross combination. A histological study of the in vitro cultured ovules revealed the development of the embryo inside the ovule in the absence of normal endosperm. The in vivo grown ovules showed a total breakdown of the developing seed within four weeks after pollination due to a postfertilization barrier. This ovule culture technique was applied in a diallel cross of seven Alstroemeria species, five from Chile and two from Brazil. The selfings and the reciprocal crosses between the Brazilian species A. inodora and A. brasiliensis were congruous and gave seed set. The cross A. inodora × A. pelegrina gave viable seeds. In all other 39 combinations no viable seeds were harvested. In those cross combinations both pre- and postfertilization barriers were found. After early ovule culture hybrid plants were obtained in 27 of the 39 incongruous species combinations of the diallel. Abbreviations: DAP - days after pollination, MS medium - medium according to Murashige & Skoog (1962) Introduction In the Netherlands Alstroemeria is an important orna- mental crop grown in greenhouses for cutflowers. The natural habitat of Alstroemeria is mainly in Chile and Brazil whereas some species are found in Bolivia, Peru, Venezuela, Paraguay and Argentina as well (Bay- er, 1987; Aker & Healy, 1990). During a period of 20 years Alstroemeria breeding companies succeed- ed in producing cultivars by interspecific hybridiza- tion. The first cultivars originated from interspecif- ic hybrids between two Chilean species: Alstroeme- ria aurea R. Graham and A. violacea Phil. (Vonk- Noordegraaf, 1981). In the classical way of interspecific hybridization a large number of pollinations was made with few full- grown seeds as the best result. Crossing barriers seem to exist both in between Chilean species, and between Chilean and Brazilian species. The present study has been carried out to detect the nature of these barriers and means to overcome them. Earlier studies on the sexual reproduction biology in Alstroemeria revealed that in the congruous situa- tion the pollen tubes enter the micropyle of the ovules one day after pollination (DAP). In some incongruous crosses pollen tube growth inhibition was complete and in other combinations incomplete inhibition was found. In the latter case it was observed that a few pollen tubes entered the micropyle, leading to aborted seeds at different stages of development (De Jeu et al., 1992). Application of an embryo rescue technique 14 DAP resulted in the isolation of true hybrids (Buitendi- jk et al., 1992). These results indicate, that the crossing barriers are of postfertilization origin. In other monocotyledonous genera such as Zephyranthes, Allium and Lilium various attempts have been made to rescue embryos from interspecific cross- es (Sachar & Kapoor, 1959; Nomura & Oosawa, 1990;