Patterns of polyembryony and frequency of surviving multiple embryos of the Brazilian pine Araucaria angustifolia

Abstract

The development of polyembryony is a common reproductive strategy in conifers. Multiple embryos are observed during early seed developmental stages. However, upon seed maturation, only the dominant embryo survives, with few exceptions. Although programmed cell death has been reported as the major mechanism responsible for elimination of subordinate embryos, the genetics of surviving embryos and the probabilities of survival remain unclear. The aim of this study is to determine patterns of polyembryony and survival frequency in Araucaria angustifolia (Bert) O. Ktze. Thus, we investigate the morphogenetic parameters that might be related to embryo survival using nuclear microsatellite markers and morphological characteristics of immature embryos and seedlings. Our novel approach couples genotype frequency analysis with the number of surviving embryos, presence of embryo dominance and number of cotyledons present within a single seed. Polyembryonic seedling frequency was low (0.022%) and 91% of surviving embryos were monozygotic. From all monozygotic embryos, 98% showed differences in growth rate (height) in relation to each other. Concrescent tissues were common in the monozygotic polyembryony patterns observed (80%) but not for those with polyzygotic polyembryony. We demonstrate that the survival of multiple embryos is a rare event in A. angustifolia seeds. To the best of our knowledge this study represents the first evidence of cleavage polyembryony in immature embryos and seedlings from A. angustifolia. Our novel approach using a combined set of morphological parameters and microsatellite markers was successful in investigating polyembryony patterns and survival.