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Structure of the pistil and pollen tube growth in Adansonia L. species: Implications for fertilization eficiency

Rasoamanana E., Razanamaro O., Verdeil J.L., Lapeyre-Montes F., Ramavovololona P., Danthu P.. 2019. Flora, 255 : p. 86-97.

DOI: 10.1016/j.flora.2019.04.005

The success of fertilization depends on an array of complex physical and physiological interactions between the pollen and the pistil. To better understand the fertilization process in Malagasy baobabs, pistil structure and pollen tube growth were investigated in three species of Adansonia: A. grandidieri (section Brevitubae), A. madagascariensis and A. rubrostipa (Longitubae section). The pistil consists of an ovary with 6¿9 locules, a very long hollow type style and six to nine lobed wet, papillate stigma. The pollen tubes grow in intercellular secretions in the stigma and join the stylar canal to reach the locule of the ovary and then the micropyle of the ovules. The size of the central stylar canal shrinks as it approaches the ovary. This restriction leads to gametophytic competition by reducing the number of pollen tubes that reach the ovules. The pollen tubes reach the ovules four to six days after pollination. The pollen tubes of the two Longitubae species grow faster than those of A. grandidieri. This information on the progamic phase of baobabs is essential to understand the mode of reproduction of baobabs.

Mots-clés : adansonia; gynécée; pollen; pollinisation; stigmate; fécondation; gamète; adansonia grandidieri; adansonia madagascariensis; adansonia rubrostipa; madagascar; pistil

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