Tomato fruit continues growing while ripening, affecting cuticle properties and cracking.

Fruit cuticle composition and their mechanical performance have a special role during ripening because internal pressure is no longer sustained by the degraded cell walls of the pericarp but is directly transmitted to epidermis and cuticle which could eventually crack. We have studied fruit growth, cuticle modifications and its biomechanics, and fruit cracking in tomato; tomato has been considered a model system for studying fleshy fruit growth and ripening. Tomato fruit cracking is a major disorder that causes severe economic losses and, in cherry tomato, crack appearance is limited to the ripening process. As environmental conditions play a crucial role in fruit growing, ripening and cracking, we grow two cherry tomato cultivars in four conditions of radiation and relative humidity (RH). High RH and low radiation decreased the amount of cuticle and cuticle components accumulated. No effect of RH in cuticle biomechanics was detected. However, cracked fruits had a significantly less deformable (lower maximum strain) cuticle than non-cracked fruits. A significant and continuous fruit growth from mature green to overripe has been detected with special displacement sensors. This growth rate varied among genotypes, with cracking-sensitive genotypes showing higher growth rates than cracking-resistant ones. Environmental conditions modified this growth rate during ripening, with higher growing rates under high RH and radiation. These conditions corresponded to those that favored fruit cracking. Fruit growth rate during ripening, probably sustained by an internal turgor pressure, is a key parameter in fruit cracking, because fruits that ripened detached from the vine did not crack.