Commercial Pistachio Production
Pistachio nuts are unique in that they remain intact within a split endocarp. The color of the nut can greatly affect its market price. Green nuts are in high demand and fetch the highest prices. For instance, the pistachio nuts of Sicily are renowned for their green color and receive double the price of standard pistachios. Nuts are sometimes dyed to hide blemishes, which is partly why pistachios were traditionally stained red. The marketing of California pistachios features the “natural pistachio”—a large nut with a naturally colored shell.
Having a blemished shell can be more than a cosmetic issue since it can indicate fungal or insect damage to the crop. Such damage can be a precursor to contamination with aflatoxins, carcinogenic fungal toxins. Nuts that are processed within 24 hours will not be contaminated with these toxins, and this is the standard process for commercially produced nuts from California.
While a number of countries grow pistachios, only a few countries are major exporters of these nuts. Iran and the United States provide 75 percent of the world’s pistachio exports, with virtually all of the United States’ nuts being grown in the Central Valley of California. Of the two, the United States is the leading exporter. The other leading exporting countries include Turkey, Syria, and China.
Pistachios were not introduced into the United States until the mid-1800s. In 1890, the U.S. Department of Agriculture introduced a number of cultivars from the Middle East to California. One was the female Kerman—named after its original location in Iran—which now comprises the nut-bearing portion of the California pistachio industry. It is complemented by the male variety Peters, named after the grower who first selected it to pollinate Kerman.
One intrinsic negative feature of the crop is its tendency toward alternate bearing. Production of a heavy crop one year will be followed by negligible amounts of nuts being born the following year. Heavy pruning of three-year-old wood will mitigate this costly trait for up to six years.
The high cost of establishing a pistachio grove in the United States has led to primarily corporate ownership of the groves. Several reasons make it highly expensive to introduce and maintain a grove of this type. In areas like the San Joaquin Valley of California, the trees transpire at a high rate due to their type of stomata. Despite their having evolved in arid regions, such commercial pistachio groves require substantial amounts of irrigation compared to those of other nuts to produce at high levels. The lack of nut production for years after the trees are planted requires a large initial capital investment that will not be repaid for quite some time.
In their native regions, pistachio trees are generally grown as seedlings, since they are stronger than those of other species. In much of the world, however, the desirable nut bearing tree is grafted onto the rootstock of one of its wild relatives. The type of rootstock used varies, depending on the local needs of the orchards. In some cases, resistance to Verticillium wilt is of paramount concern, while other orchard managers are more concerned about tolerance to salinity. In the United States, rootstocks include the species Pistacia terebintus, Pistacia atlantica, Pis- tacia integerrima, and a hybrid of Pistacia atlantica and Pistacia integerrima. These particular grafts provide enhanced disease resistance. Iranian orchards tend to utilize rootstocks of Pistacia mutica and Pistacia khinjuk.
The nuts are generally harvested by shaking the trees. In much of the world, the trees are manually shaken. Large, commercial groves often utilize mechanical shakers to release the nuts from the trees. Frequently, the nuts are subsequently sun dried.
California’s commercial pistachio industry did not produce enough nuts to be competitive on the world market until 1976. In just 31 years, California’s industry grew to produce 207,810 tons of pistachios. The total value of the U.S. crop for 2007, which was produced almost entirely in California, was $557 million. Despite having produced over half a billion dollars’ worth of pistachio nuts, the United States is not the world’s leading exporter of this delicacy. That title belongs to Iran.
Unlike the United States’ monoculture of female pistachio trees, Iran is a center of genetic diversity for this species. The most important area of nut production in this country is the Kernan Province, where over 70 cultivars are in production. Despite this industry’s location in the region of origin of the pistachio, their cultivation was economically unimportant until the 1930s. There is currently a rapidly expanding profusion of orchards, with major cultivars including Ouhadi, Kalleh- ghouchi, Ahmad Aghaii, Akbari, and Badami Zarand.