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ISHS Acta Horticulturae 419: I International Symposium on Pistachio

THE DEVELOPMENT OF EARLY SPLIT PISTACHIO NUTS AND THEIR CONTAMINATION BY MOLDS, AFLATOXINS, AND INSECTS

Authors:   M.A. Doster, T.J. Michailides
Abstract:
Early splits (ES) are abnormal pistachio nuts that have both the hull and shell split exposing the kernel to invasion by insects and molds (especially those that produce the potent toxins aflatoxins). Five commercial orchards out of the eight tested had detectable levels of aflatoxins in ES before harvest. Therefore, it is important that these contaminated nuts are removed during processing. ES with shriveled hulls had more than twice the navel orangeworm (NOW) infestation, more than twice the mold, and more than 99% of the aflatoxins compared to ES with smooth hulls. The shriveled hull is a characteristic that allows the identification of the pistachio nuts most likely to have aflatoxins and could be used to remove these contaminated nuts. NOW-infested kernels accounted for 84% of the aflatoxin in the pistachio nuts. Reduction of NOW by growers should reduce aflatoxin levels in harvested nuts. ES formed over a several week period prior to harvest. The earlier the ES formed the more mold and NOW present in the kernel. Fortunately, these early formed ES are very distinct from normal nuts by several characteristics (weight, size, shell discoloration, hull shriveling). Any of these characteristics could be used during processing to remove pistachio nuts with moldy and NOW-infested kernels. Skipping one irrigation in mid May (period of shell formation) substantially increased the percentage of ES observed at harvest but did not affect normal shell splitting. Therefore, growers should take extra care that sufficient irrigation is applied in late spring to reduce the numbers of undesirable ES at harvest.
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