During development of commercially valuable plant organs and after their harvest, natural disease resistance (NDR) generally declines leading to inevitable infection, disease and ultimately death. In horticultural produce, postharvest diseases caused by fungi usually begin as either latent infections established in the field or wound infections during subsequent harvesting and handling. A decline in NDR can activate quiescent in-fections and increase disease incidence/severity. Four sets of factors affect the decline of NDR in produce after harvest (Prusky, 1996): (1) nutritional requirements for the pathogen; (2) preformed antifungal compounds (phytoanticipins); (3) the potential for inducible antifungal compounds (phytoalexins); and (4) activation of fungal pathogenicity factors. Factors 1 and 4 tend to be enhanced as tissues ripen and/or senesce, while factors 2 and 3 tend to be suppressed. Many preformed and/or inducible defence mechanisms are involved in the NDR of harvested horticultural fruit, vegetable and ornamental crops