Morphological and histological impacts of the laurina mutation on fructification and seed characteristics in Coffea arabica L.

Abstract

Key message The comparison between the cultivar Bourbon and its mutant, the Bourbon pointu, of Coffeaarabica led to five novel findings on fruit developmentand three main impacts of the mutation.Abstract Coffea arabica ‘Laurina’ (Bourbon pointu) is anatural mutant of Coffea arabica ‘Bourbon’. Relative to the‘Bourbon’ cultivar, it is characterized by internode dwarfism,a Christmas tree shape, and lower caffeine content. Theeffects of the laurina mutation on fructification over time, thefruit structure and seed characteristics were studied here.Fruits of ‘Bourbon’ and ‘Bourbon pointu’ were monitored.The trees were grown in the same plot and flowered on thesame day. Harvesting was done every 2 weeks from the 6thto the 26th week after flowering. Histological observationswere carried out using multiphoton and conventionalmicroscopes. The measurements concerned the fruit,parchment and seed. Five novel findings on fructificationdevelopment were obtained: (1) a sigmoid model and nonlinearregression efficiently described the phenomenon; (2) aprecise relationship was defined between the qualitativestages of fructification and quantitative observations, thusrevealing key weeks in this process; (3) the parchment had amesocarpic origin; (4) a meristematic zone was present closeto the parchment; and (5) an endocarp with three cell layerswas visible in young fruits. Three effects of the laurinamutation were highlighted: (1) fruit growth ended 1 weekearlier in ‘Bourbon’, but without difference in fruit length. Incontrast, fruits were wider on average in ‘Bourbon’; (2) theparchment of narrow seeds in ‘Bourbon pointu’ was thickerthan in other ‘Bourbon pointu’ and ‘Bourbon’ seeds; and (3)the narrow seed frequency in ‘Bourbon pointu’ depended onenvironmental conditions.