Microscopic characterization of American oil palm (Elaeis oleifera (Kunth) Cortés) floral development

Little is known about the anatomical development of the reproductive system of the American Oil Palm (Elaeis oleifera); an species known in Brazil as Caiaué, that holds a series of characteristics not found in the African Oil palm (Elaeis guineensis), rendering it as an important source of genetic variability to be explored by African Oil palm breeding programs in Brazil and elsewhere. Among those characteristics are its small stature, resistance to the Bud Rot and high oil quality. The main objective of this study was to conduct a histo-anatomical analysis of the complete development of the reproductive system of three E. oleifera individuals collected at different localities in the Brazilian Amazon forest. Besides that, rachillas collected from different leaf axils were analyzed to determine the meiotic stage of microsporocytes useful for future cytogenetic and cloning studies. The microscopy analysis of the American Oil Palm individuals BR174, Coari and Manicoré started with the youngest phase of the inflorescence until it reached its full development. Flowers were collected from inflorescences in different stages of development and from different parts of a rachilla, fixed and embedded in Technovit 7100® resin and/or paraffin. Ultrathin longitudinal and cross sections of the inflorescences were performed for comparison between individuals with light or phase contrast microscopy. For Scanning Electron Microscopy, flowers were dissected from different parts of a rachilla, fixed, critical point dried, metalized with a nanolayer of gold/palladium and analyzed in a Scanning Electron Microscope Zeiss DSM 962. Results obtained showed the same pattern of floral development previously reported for the African oil palm; however, punctual and temporal variations occurred among the three individuals. The meiotic development in male flowers occurs in an acropetal way in this species, and leaf +14 turned out to be the one were most meiotic stages were identified, rendering it as the ideal stage for collecting samples for cytogenetic studies as well as for tissue culture aiming the production of haploid plants.