Flora 243 (2018) 88–100 Contents lists available at ScienceDirect Flora journal homepage: www.elsevier.com/locate/flora Microscopic characterization of American oil palm (Elaeis oleifera (Kunth) T Cortés) floral development Marcelo Picanço de Fariasa, Guy de Capdevilleb, Rosana Falcãob, Priscila Borges de Moraesb, André Pereira Leãob, Julcéia Camilloc, Raimundo Nonato Vieira da Cunhad, ⁎ Alexandre Alonso Alvesb, Manoel Teixeira Souza Júniorb, a Universidade Federal de Lavras – UFLA, Lavras, MG, Brazil b Embrapa Agroenergia, Brasília, DF, Brazil c Universidade de Brasília – UnB, Brasília, DF, Brazil d Embrapa Amazônia Ocidental, Manaus, AM, Brazil ARTICLE INFO ABSTRACT Edited by Alessio Papini Little is known about the anatomical development of the reproductive system of the American Oil Palm (Elaeis Keywords: oleifera); an species known in Brazil as Caiaué, that holds a series of characteristics not found in the African Oil Elaeis guineensis palm (Elaeis guineensis), rendering it as an important source of genetic variability to be explored by African Oil Inflorescence palm breeding programs in Brazil and elsewhere. Among those characteristics are its small stature, resistance to Caiaué the Bud Rot and high oil quality. The main objective of this study was to conduct a histo-anatomical analysis of Microsporocytes the complete development of the reproductive system of three E. oleifera individuals collected at different lo- Cytogenetics calities in the Brazilian Amazon forest. Besides that, rachillas collected from different leaf axils were analyzed to In situ hybridization 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. 1. Introduction Considering the current taxonomy of the palms, the genus Elaeis is one of the 18 genus of the Cocoseae tribe, which is one of the six tribes Oil palm (Elaeis guineensis Jacq.), a species originated in West Africa, of the Arecoideae subfamily; one of the five subfamilies of the and well adapted to several other tropical areas in Southeast Asia and Arecaceae family, the Palm Family (Hai, 2016). This genus consists of South America, is today the world’s biggest source of vegetable oil. two species, E. guineensis (or African oil palm) and E. oleifera (or Altogether, palm oil and palm kernel oil, accounted for 66.99 million American oil palm), with a pantropical distribution, but with two dis- metric tons of the vegetable oil consumed worldwide in 2016/17 tinct diversity centers, Malaysia and South America, respectively (Statista–The Statistics Portal, 2017). Triacylglycerol is the major con- (Eiserhardt et al., 2011). stituent of palm oil and palm oil kernel, and has a broad and traditional Floral characteristics have high taxonomic value in the Arecaceae use in many important industries, such as the food and the biofuels family, because they help to delimit monophyletic groups, as in the industries (Acevedo et al., 2015). genus Chamaedorea, which has a large number of species (Askgaard ⁎ Corresponding author. E-mail address: [email protected] (M.T. Souza). https://doi.org/10.1016/j.flora.2018.04.005 Received 8 June 2017; Received in revised form 4 April 2018; Accepted 12 April 2018 Available online 13 April 2018 0367-2530/ © 2018 Elsevier GmbH. All rights reserved. M.P. de Farias et al. Flora 243 (2018) 88–100 et al., 2008) and in the genus Raphis, in which two groups may be hybrids, when comparing with E. guineensis, which affect insect polli- distinguished by the characteristics of the stamen filament (Giddey nation (Meléndez and Ponce, 2016); and yet, that there are no studies et al., 2009). According to Tomlinson (1990),inflorescences from the on the development of the reproductive organs of E. oleifera, which can family Arecaceae are divided into two groups: the first one, Hapax- tell how different is the reproductive development between them, and anthy, the inflorescences are originated from the apical meristem, how it might affect the economical use of the interspecific hybrids, this which is induced to initiate the reproductive phase after a long vege- present work had as main objective to conduct an histo-anatomical tative period. The flowering period is short and usually ends with the study of the complete development of the reproductive system of the death of the whole plant at the end of the flowering cycle. Hapaxanthy American oil palm, filling a gap of knowledge that certainly has po- inflorescences occur in about 5% of palm species. The second one, tential to further strength the use of this species in breeding programs. which occurs in 95% of the palm species, is the Pleonântic in- Additionally, as we conducted the studies on the development of E. florescence, which is produced continuously from an indeterminate oleifera male flowers, we identified the leaf where was possible to iso- apical meristem. Such growth starts from the interfoliar meristems late a wider range of meiotic stages, allowing to follow the path of (Adam et al., 2005). development of microspore mother cells until the production of mature Inflorescences may be branched or in spikes, with variations in their pollen grains, and finding out the best stage to collect meiotic micro- bracts, bracteoles, and prophyll. Flowers in different stages of diclinous spore mother cells in pachytene stage and mature pollen stage for future species (two types of flowers, male and female, positioned on distinct cytogenetic and tissue culture studies, respectively. flower receptacles) may occur in both dioecious and monoecious in- dividuals. Also, different organization patterns of the flowers on the 2. Material & methods rachis and rachillae are common (Dransfield et al., 2008). Both species of the genus Elaeis are monoecious species (male and female re- 2.1. Plant material productive organs on different parts (e.g. flowers) of the same plant rather than on separate plants) in which male and female flowers are The plant material used in this study was collected from to the produced during distinct sexual cycles (Dransfield et al., 2008; Cunha American oil palm Germplasm Bank maintained at the Rio Urubu et al., 2009). Experimental Station - Embrapa Western Amazon, located 140 km from In general, the gynoecium species in the Arecaceae family have Manaus, in the municipality of Rio Preto da Eva, Amazonas, Brazil, three carpels, although polyandry is a common phenomenon in the latitude 2°35′ S, longitude 59°28′ W and altitude 200 m. The climate is family (Dransfield et al., 2008). For the subfamily Arecoideae, the or- tropical, and, according to the classification of Köppen & Geiger is Af ganization of diclinous species flowers in sympodial cluster known as (Climate-data.org, 2018). The average annual temperature is 27.3 °C, triad, in which a central pistillate flower becomes associated with two with a maximum average temperature of 32.4 °C and a minimum of lateral staminate flowers, is considered a possible synapomorphy (Uhl, 22.6 °C. The average annual relative humidity is 85% and the annual 1976; Dransfield et al., 2008; Ortega & Stauff er, 2011). For the tribe average total insolation is 1,940 h. The average annual rainfall is ap- Cocoseae, synapomorphy is characterized by the presence of stami- proximately 2300 mm. According to the Brazilian classification of soils, nodes that merge themselves forming a ring around the ovary, besides the soil in this area is a yellow Latosol with a very clay texture 2:1 the formation of the spathe which surrounds the inflorescence. Dicli- (Miranda et al., 2001). nous species in some flowers happens due to the abortion of the sta- This Germplasm Bank has samples collected from 19 distinct lo- mens leading the flowers to a unisexual condition (Mitchell & Diggle, calities in the Brazilian Amazon forest, and each sample collected (seed 2005). This fact occurs due to the interruption of the cell division in the from one tree) was established as a family of half-siblings with an tissues responsible for the production of stamens and carpels (Daher average of 10 plants per family (each family was classified as a sub- et al., 2010). However, it is possible that no cell death occurs in the sample). Individuals from three distinct localities, BR174, Coari and tissues of those organs. Studying the floral development of E. guineensis, Manicoré, were used in this study. Adam et al. (2005) identified the development of triads in the female Inflorescences of BR174, Coari and Manicoré in different re- plant; however, the staminate flowers become sterile at the end of the productive development stages were collected from plants of 26, 8 and development. 26 years old, respectively; one plant per locality. The same numbers Few histological studies were published where the entire re- attributed to the leaves were used to identify the inflorescences.