Pistachio - Pistacia vera
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TAXONOMY

The cultivated pistachio, Pistacia vera L., is a member of the Anacardiaceae or cashew family. Other important members of this family include cashew, mango, mombins (Spondias spp.) poison ivy, poison oak, and sumac.

Cultivars
    Pistachio trees are dioecious, meaning that there are separate male and female trees. The standard male cultivar is ‘Peters', the primary pollinizer for 'Kerman', the main female cultivar.  The pistachio industry is reminiscent of sour cherry in that commercial production in the USA is based on a single cultivar, ‘Kerman'.

ORIGIN, HISTORY OF CULTIVATION

    The pistachio is native to the Asia Minor area, from the islands of the Mediterranean in the west to India in the east. It probably developed in interior desert areas, since it requires long, hot summers for fruit maturation, is drought and salt tolerant, yet has a high winter chilling requirement. The pistachio has been considered a delicacy since the beginning of recorded history, and has been cultivated for centuries throughout its native range. It was introduced to California in 1854, but commercial plantings did not develop until 1970. Today, pistachios are grown primarily in California, although there is some production in Arizona, New Mexico, and western Texas.

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PRODUCTION

World (2002 FAO) - 571,150 MT or 1.2 billion pounds. Pistachios are produced commercially in 18 countries on 1.1 million acres.  Worldwide average yields are 1050 lbs/acre.

Top 10 countries
(% of world production)
1. Iran (52%) 
6. Greece (2%)
2. USA (24%)
7. Afghanistan (<1%)
3. Syria (9%)
8. Italy (<1%)
4. Turkey (7%) 9. Uzbekistan (<1%)
5. China (5%) 10. Tunisia (<1%)

United States (2004 USDA) - 158,182 MT or 348 million pounds. Virtually all pistachio production is in California [Statistics are for California only]. Small acreages exist in Arizona, New Mexico, and western Texas. The industry value is $438 million. Bearing acreage is 93,000. Yield is 1700 to 3300 lbs/acre, depending on "on" or "off" status of the crop. Price paid to growers was $1.26/lb.

BOTANICAL DESCRIPTION


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Plant
    Pistachios are small to medium sized dioecious trees, obtaining heights of  20 ft but generally smaller in cultivation. Leaves are pinnately compound, generally with 5 leaflets, each broadly oval with entire margins and obtuse tips.

Flowers
    Male and female flowers are borne on separate plants. Inflorescences of several hundred tiny, brownish-green flowers are borne laterally on 1-yr wood. Flowers lack petals, and have up to 5 sepals. Males have 5 stamens, and females lack stamens, and have a single tricarpellate, superior ovary. The inflorescence is a panicle in both cases with 13 primary branches, each bearing 1 terminal and 5-19 lateral flowers. Most fruit set occurs from terminal flowers. Fruit set averages about 10%.




Male (left) and female (right) inflorescences of pistachio [photos courtesy of Dr. Louise Ferguson, University of California, Davis]

Pollination
    Pistachios are wind pollinated. Although bees may be attracted to male flowers for pollen, they are not attracted to females since they lack pollen, nectar, and petals. Pollinizers (males) are often planted in the center of a 3 x 3 square of females, yielding an 8:1 ratio, or sometimes ratios up to 24:1 are used.

Fruit
    Botanically, the fruit is a drupe, although marketed as a nut. The hull is thin and fleshy, pale tan in color with a red blush at maturity. There are 3 disorders related to fruiting in pistachio:

   Blank production. "Blanks" are fruits without kernels (parthenocarpic fruit). Blank percentage averages 20% in 'Kerman'.

    Lack of shell splitting. One unique feature of pistachios among other nut crops is that the endocarp (shell) splits naturally prior to maturity. The  percentage of splitting ranges from 50-75% in ‘Kerman', and can be reduced by drought stress. Nuts with unsplit shells are removed and cracked mechanically.

    Alternate bearing. Pistachios produce heavy crops every-other-year, alternating with little or no crop in "off" years. The cause is unlike that in fruit crops such as apple, pecan, prune, or olive, where carbohydrate depletion and/or hormonal factors inhibit floral initiation in the summer of an "on" year. In pistachio, inflorescence buds are initiated, develop partially, but then abscise during heavy crop years, making it impossible to produce a crop the next year. As with blank production, rootstock is known to have a significant effect.




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GENERAL CULTURE

Soils and Climate
    Pistachio production is best on deep, well-drained loams with high lime content and pH. Pistachios are more tolerant of alkaline (Na+) and saline soil than most tree crops. Soils with a history of Verticillium (poorly drained, old cotton land) should be avoided or fumigated prior to planting.
    Pistachios are truly Mediterranean in adaptation; they thrive in the hot, dry, desert-like conditions, such as the central California valley. Trees are highly disease prone, and rain or even high humidity during the spring and summer promotes severely debilitating diseases. Chilling requirement is relatively long, 1000 hr. Thus, arid climates with rather cool, prolonged winters are needed for pistachios. Cold hardiness ranges around 5-15 F in mid-winter in California, but has been reported to reach 0 F in Iran.

Propagation
    Pistachios are most commonly T- or chip-budded onto 1-yr or 2-yr seedling rootstocks.

Rootstocks
    Seedlings of P. atlantica and P. terebinthus were traditionally the most popular stocks, with the former more readily available and easier to bud. P. terebinthus is more cold hardy and used by growers in colder areas. Both are susceptible to Verticillium wilt, and many orchards originally planted with these stocks have died. P. integerrima and hybrids of this species with P. atlantica, are vigorous stocks with resistance to Verticillium wilt. These are called Pioneer Gold and Pioneer Gold II.

Planting Design, Training, Pruning
    Most commercial orchards in California are planted to square or triangular arrangements with a variety of spacings, 11 to 30 ft between trees. Many growers use filler trees at spacings of 11-22 x 22-24, removing every other row at 12-15 years.  Training is open center or modified leader. Training during the first 5 years is important for establishment of a full canopy of fruiting wood. Due to strong apical dominance, heading cuts must be used to stimulate branching, otherwise, long, weak branches develop and the tree gradually becomes poorly shaped and low yielding. Also, older pistachios produce very few lateral vegetative buds, and thus it becomes very difficult to induce branching by pruning older trees.

HARVEST, POSTHARVEST HANDLING
Maturity
    The skin changes from translucent to opaque, and the mesocarp becomes loosened from the shell when nuts are mature. Highest quality is obtained when harvest occurs within 7-10 days of this stage. Later harvest results in more stained shells and navel orangeworm infestation.

Harvest Method
    Young trees (<10 yr) are too fragile to be harvested by trunk shakers, so are harvested by hand knocking onto canvas sheets. Mature trees are harvested by conventional shake-harvest equipment used for almonds.

Postharvest Handling, Storage
    Harvested fruit must be hulled and dried within 24 hr to avoid shell staining and aflatoxin contamination. Fruit are fed through machines that have 2 parallel, rubberized belts rotating at different speeds. Hulled nuts are floated and washed, and hulls are often composted and used for fertilizer. Nuts are dried in large forced-air driers to a moisture content of  5%, and stored in large bins until roasting. Pistachios can be stored for months in a dried state.

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CONTRIBUTION TO DIET

    Pistachios are marketed primarily as in-shell nuts, due to the ease with which nuts can be opened without cracking. This accounts for 80% of pistachio utilization. The remaining 20% is marketed as shelled nuts, which are also sold fresh, or processed into candies, baked goods, and ice cream. Per capita consumption of pistachio was 0.29 lb/year in 2004.

Dietary value, per 100 gram edible portion

Pistachio nuts
Water (%) 5.3
Calories 594
Protein (%) 19.3
Fat (%)
52
Carbohydrates (%)
19
Crude Fiber (%)
2

% of US RDA*
Vitamin A
4.6
Thiamin, B1 48
Riboflavin, B2
1.9
Niacin
7.8
Vitamin C
0
Calcium
16
Phosphorus 62
Iron 73
Sodium ---
Potassium 21

* Percent of recommended daily allowance set by FDA, assuming a 154 lb male adult, 2700 calories per day.

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