CHARACTERIZATION OF DFD (DELAYED FRUIT DETERIORATION): A NEW TOMATO MUTANT

Abstract

Fruit softening is a complex physiological event and a major determinant of postharvest fruit quality. Attempts to understand the molecular basis of softening have focused on cell wall metabolism and it is now generally believed that fleshy fruits soften as a consequence of polysaccharide degradation in the primary cell wall and middle lamella. Tomato has provided the principal model system for these studies and yet efforts over the last ten years to substantially reduce softening in transgenic tomato lines by suppressing the expression of genes encoding cell wall degrading proteins, such as polygalacturonase (PG), pectin methylesterase (PME) and expansin, have been largely unsuccessful. We have recently identified a tomato line that we named the DFD (delayed fruit deterioration) mutant, which promises to provide a new perspective of the key molecular determinants of softening and other postharvest quality traits. The two major characteristics of DFD are substantially reduced fruit softening and complete resistance to postharvest disease, which collectively result in a remarkable shelf life. Unlike other well known ripening-related tomato mutants such as rin (ripening inhibitor) and nor (non-ripening), DFD fruits undergo essentially normal climacteric ripening while attached to the plant, with all the organoleptic characteristics and quality properties that are essential for commercialization, such as color, aroma and accumulation of sugars. However, the DFD fruits also maintain a firm texture for a dramatically extended period of time after harvesting and can be stored with no further treatment at room temperature for more than seven months with any signs off deterioration. Moreover, after more than one year, intact and untreated DFD tomatoes show no signs of microbial infection. These data suggest the need for a new model to understand the key features that underlay tomato fruit softening and tissue disintegration.