Pericarp tissue microstructure and cell wall polysaccharide chemistry are differently affected in lines of tomato with contrasted firmness

The contribution of tissue histology and cell wall polysaccharides chemistry to describing ripe tomato fruit texture was addressed in near isogenic lines of fruits harboring firmness QTL. These lines were constructed in Levovil (L), VilB (B), M82 (P) and Moneyberg (Mbg) genetic backgrounds and carried introgressed fragments from three origins on chromosomes 2, 3, 4, 5 or 9 (and two sub-regions a and b). The firmness of their pericarp tissue was measured by compression testing and related to cell size distribution and to published data on their cell wall polysaccharide chemistry. The pericarp tissue from all L9 lines, B9 and P3.4 was firmer than the respective parental line while that from Mbg9 and P9.2.5 was softer. The pericarp tissue from L4, L4a and Mbg5 fruit was made of larger cells while that from Mbg2 and Mbg9 had smaller cells than their parents. Correlations were found between firmness and cell size distribution for QTLs only in the Levovil group. Correlations between firmness, histological characteristics and cell wall polysaccharide chemistry indicate positive relations between glucose-containing polysaccharide (cellulose and hemicelluloses) contents and pericarp tissue thickness. Other positive relations were found between galactosylated pectins and hemicelluloses and firmness in QTL lines of the Levovil background. The results show that chromosomes 9, 5, 4 and 2 are associated with pericarp histology in these lines and that pericarp tissue firmness depends on histology and cell wall chemistry according to genetics. These tomato lines represent good models to study the complex contributions of turgor pressure, cell wall chemistry, tissue architecture and their mechanisms of modulation underpinning texture in ripening tomatoes.