Factors affecting seed germination of Ilex latifolia and I. rotunda

Abstract

Mature seeds of Ilex species usually contain immature embryos and are extremely difficult to germinate. Ilex latifolia and I. rotunda, two species that are grown as ornamentals, also produce seeds that are difficult to germinate. In the present study, we investigated some factors affecting seed germination in those species. Although seeds of I. latifolia and I. rotunda could imbibe water, they did not germinate. When embryos were cultured in vitro, germination was observed in I. latifolia but not in I. rotunda. Interestingly, a transient decrease in germination frequency occurred in I. latifolia embryos isolated from seeds collected in September or October. Among five types of I. latifolia seeds that differed in the presence of the endocarp, testa, and endosperm, germinability of isolated embryos was highest. Good germination was also observed in quarter-seeds with or without endocarp followed by half-seeds. Treatment of seeds with sodium hydroxide (NaOH) had no effect on seed germination in I. latifolia. Cold stratification at 5 °C increased the germination frequency of I. latifolia embryos. In conclusion, the data suggested a mechanical barrier by the endocarp and inhibitors contained in the endosperm, testa, and/or endocarp inhibited seed germination in I. latifolia. Although no seeds or embryos of I. rotunda germinated, cold stratification in combination with other treatments deserves further investigation. Chemical name: sodium hydroxide (NaOH).