Analysis of dwarfism at the microscopic level in C. arabica cv. Laurina

Most Arabica varieties cultivated worldwide belong to the Typica or the Bourbon groups. In the island of Réunion, a dwarf Bourbon tree appeared, which is known as the Bourbon pointu (or the Laurina variety), due to the so-called Laurina mutation. The internode length - more than internode number variations - mainly account for plant size difference between the two varieties. The aim of this study was to explain internode length differences due to the Laurina mutation in terms cell size and cell number. Histological analysis results showed that the two varieties (Bourbon vs Bourbon pointu) differed in two main aspects: 1/ smaller and fewer cells in Bourbon pointu; 2/ In both varieties, due to their lignification, the internodes reached their final size, after two new internodes had been emitted from the apex. In Bourbon, stem growth occurred via cell division (meresis) in the last emitted internode, then to cell elongation (auxesis) in the previous one (classical kinetic of growth), whereas in Bourbon pointu, growth was due to meresis only (almost no auxesis) in the two last internodes. Understanding the physiological mechanism controlling dwarfism in the Bourbon pointu variety will be our next challenge. Internode growth is generally under the control of plant hormones. We hypothesize that the Laurina mutation could modify internodes growth towards a modified plant growth regulation. (Résumé d'auteur