Postharvest losses of fruits and vegetables are even higher and are estimated to be 40–50%. Postharvest fruit rotting are a major cause of those losses and are chiefly caused by fungal pathogens after fruit ripening. However, in postharvest diseases fruit ripening is another major component that will determine fruit resistance. The molecular trigger induces the germ tube to differentiate an appressorium. Postharvest diseases of fungal origin produce one or more of the following pectic enzymes: pectin esterase, endo- or exopolygalacturonase, endo- or exopectate lyase, and endopectin lyase. The endopectin lyases are produced almost exclusively by fungi, while endopectate lyases are produced primarily by bacteria. The mechanism found in avocado may have equivalents in other postharvest pathosystems and suggests new approaches for breeding against and controlling postharvest diseases. Various stages of postharvest disease development include contamination, the inoculum reaches the host, usually by spreading of spores; penetration, the pathogen enters through the tissue of the host by means of penetration structures.