Relationship between shell discoloration of pistachio nuts and incidence of fungal decay and insect infestation

Shell discoloration of pistachio (Pistacia vera) nuts collected from commercial orchards and processing plants was related to fungal decay and insect infestation of the kernel. Nuts with ruptured hulls (early split nuts and nuts with cracked hulls) varied considerably in the amount of shell discoloration, ranging from none to extensive. For both types of hull rupture, as shell discoloration increased, kernel decay also increased. Nuts with no discoloration had little or no fungal decay and navel orangeworm (Amyelois transitella) infestation. Processed nuts with an oily-shell appearance had the highest incidences of fungal decay and navel orangeworm infestation; nuts with a crinkled shell, nuts with extensive dark brown discoloration, and nuts with moderate dark brown discoloration along the suture had relatively high levels of decayed and infested kernels; while nuts with yellow discoloration, nuts with moderate dark brown discoloration not along the suture, and nuts with no discoloration had little or no decay and infestation. Also, as shell discoloration of processed nuts increased, kernel decay increased. Our results suggest that shell characteristics may be used by processors to identify poor quality nuts and to improve the quality of pistachio nuts sold to consumers.