Catharanthus roseus [L.] G. Don: Allogamy as the main reproductive strategy and autogamy as a supposed reproductive guarantee mechanism.

• We present a new proposal, the so-called reproductive efficiency, which measures plants' efficiency in fertilizing their eggs. • We apply microsurgeries to the corolla tube to enable artificial self-fertilization. • Catharanthus roseus presents the mixed reproduction mode, namely: allogamy and autogamy, simultaneously. • We conclude that allogamy is the main pollination strategy. • Autogamy is a reproduction guarantee mechanism (back-up plan) that can be reinforced by cleistogamy. Despite the medicinal importance of Catharanthus roseus [L.] G. Don., the literature is still controversial about its mode of reproduction. The breeding of species depends on this information. The purpose of this study was to ascertain the preferential reproduction mode of C. roseus by using different genotypes of this species. We also sought to verify the relative importance of allogamy and autogamy on the species reproduction. Therefore, it was necessary to estimate the pollen:ovule ratio, the rates of open pollination and natural self-fertilization, the efficiency of allogamy and autogamy, and pollen viability and stigma receptivity. Furthermore, we applied fluorescence microscopy to analyze the emission and development of pollen tubes in vivo in floral buds and investigated the histochemistry of the pollen grains. Finally, through ISSR markers, we estimated the genetic diversity of the genotypes. In general, C. roseus has a mixed reproduction mode, with the possible simultaneous occurrence of allogamy and autogamy. However, allogamy was much more prevalent, and it was also more efficient as a reproductive strategy in the genotypes. The high magnitude of genetic diversity found corroborates allogamy as the most prevalent mode of reproduction. Nevertheless, autogamy occurred in all the genotypes, although the seed production efficiency was low. Autogamy can be understood as a supposed reproductive guarantee mechanism by C. roseus. [ABSTRACT FROM AUTHOR]