Could the California pistachio industry benefit from germplasm and soils research data collected in Iran?

Hossein Robani, who farms 300 acres of pistachios at Delano, Calif., says it could, since trees that grow in the rocky, alkaline, and water-starved soils of Iran have traits that could improve the limited selection of varieties and rootstock used in California.

Robani told growers at a recent University of California Cooperative Extension meeting in Parlier that Iranian scientists have much research data that is seldom put to use. The political volatility of the Middle East, of course, clouds any potential technology transfer for the time being.

“Maybe we could find some plant material that requires less chilling hours and is more resistant to diseases and pests than our Kerman variety,” he said.

Exposure to sufficient cold temperatures or chilling during late fall and winter is critical for pistachio bloom and production the following spring in California.

Female Kerman trees, with Peters variety pollinators, are the standard for the state's 98,000 acres of pistachios.

Robani based his comments on what he learned at a symposium on pistachio growing held in Iran in May of 2005 by the International Society of Horticultural Science. Delegates toured orchards and research facilities in the Rafsanjan area, the center of Iranian pistachio production.

Pistachio trees there are bushy, a mere 5 to 6 feet high, planted a few feet apart, irrigated only once or twice per season, and harvested by hand by family-farm owners, each having only a few acres. Nuts are dried in the sun, bagged, and stored to await favorable prices.

Yields there are said to be no more than 1,000 pounds per acre, versus “on-year” average production in California that has exceeded 3,500 pounds per acre in recent years.

The end product differs from the typically smooth, buff- colored shells and crisp texture of California nuts and is often dyed red or green to mask staining before being sold at retail. Iranian pistachios, however, do have a gourmet following which prefers their taste.

Robani contends that Iranian pistachio researchers want nothing in return for their information and would be willing to share it for the sake of cooperation.

He says the Iranian researchers have nothing like Cooperative Extensions to disseminate new information to their growers, who are not likely to change their production methods, anyway.

Rejecting any notion that Iranian producers want to penetrate California's markets, he also said the price of pistachios — even in Iran — is too high and their quality is too poor, to compete with California's. He said he saw pistachios sold in Tehran at $13 for 1 kilogram, or nearly $6 per pound.

The high duties on Iranian pistachio imports, applied by the United States several years ago to prevent dumping at below-market prices, remain in place, although some Iranian product may enter the United States via European merchants.

Louise Ferguson, University of California Cooperative Extension pomologist at Parlier, also attended the pistachio symposium at Tehran and agreed with Robani on the value of information collected by Iranian researchers.

She predicted that as agricultural water supplies and quality decline in California, pistachios will be grown here more like they are in Iran.

“We have a lot to learn about pistachios and soil-water chemistry. We pour water and fertilizer into our trees that generate growth and we then have to spend more to prune. None of the trees in Iran are pruned,” she said.

Ferguson also spoke at the grower meeting, explaining how winter chilling affects California pistachio production.

“The function of chill, basically, is to allow a perennial crop to survive cold, to grow vegetatively and to reproduce. Pistachio is a deciduous, temperate tree that originated in northwestern Asia, but we are growing it here in a subtropical region, so we are flirting with having too little chill,” she said.

When winter chill is insufficient, vegetative bud break is delayed and uneven, bloom is poor and pollen viability is weak.

The most common chill-measuring system for pistachios in California is the number of hours at less than 45 degrees F. The bulk of research data has been collected using it. Two other systems have been developed but give results that are often too high or too low for California conditions.

A series of experiments from 2001 through 2005 on branches placed in growth chambers for control of temperature and light, matched average temperatures during the bloom period of April 10-25 for the previous 15 years.

Ferguson and other researchers learned from these experiments that for Peters pollinators, less than 600 hours at less than 45 degree F resulted in very little bloom.

When the branches were kept for more than 900 hours, they produced good bloom, good pollen viability and good cluster growth.

These and subsequent trials showed that male Peters needs 50 to 100 more chill hours than female Kerman. When the hours are 900 or more, Peters is able to synchronize bloom well with Kerman, which needs a minimum of about 650 hours.

Turning to what growers can do to maximize chill accumulation, Ferguson said fertility should be within optimum ranges for nitrogen and zinc.

Rootstocks can also affect chill accumulation, and the trials indicated UCB-1 was most responsive to less chill, Integerrima was intermediate and Atlantica was least responsive.

Application of a heavier grade of Volck oil intended for scale control on dormant pistachio trees has enhanced bloom, but Ferguson said it should only be considered when chill is marginal, the crop appears to be heavy and scale is present. “It's not going to give you that much if the buds are not there.”