Influence of pollination on seed content and mealiness development in ‘Forelle’ pear as detected with X-ray micro- and nano-computed tomography (CT)

Abstract

'Forelle' pear fruit is prone to mealiness. The aim of this study was to establish whether pollination and seed development influence the mealiness and tissue structure by characterising microstructural differences using X-ray computed tomography (CT). Flowers of five mature 'Forelle' trees were emasculated and hand cross-pollinated with 'Early Williams Bon Chretien' pollen. Another five trees were emasculated without hand pollination. After harvesting and storage for 8 weeks at -0.5°C and subsequent ripening for 7 d at 20°C, nine pollinated and nine unpollinated pears were subjected to X-ray CT. A non-destructive X-ray micro-CT was used to visualise the internal structure of the whole fruit and to investigate seed development and density variations in regions next to viable or aborted seeds. A source voltage of 100 kV and electron current of 100 μA resulted in a resolution of 75 μm. Additional high resolution (3 μm) scans were performed on a section of the neck and equator, respectively. Nano-CT allowed for characterisation and quantification of microstructural parameters at cellular level. Fruits without viable seeds was more prone to mealiness compared to fruit with viable seeds. Differences in tissue density next to viable and aborted seeds were observed, with the region next to viable seeds being denser. Pollinated fruit had a lower porosity, indicating that these fruits may have a better source of hormones due to the viable seeds, resulting in lower mealiness incidence. Mealiness is associated with a high porosity and larger cells. Although not significant (P>0.05), fruit from unpollinated flowers was associated with larger cells, higher porosities and low connectivity between cells. This study demonstrated that X-ray CT is useful for characterising and quantifying microstructural differences related to mealiness in seeded and parthenocarpic 'Forelle' pears.