Postharvest - Pistachio
Pistacia vera L. is the only species of the 11 in the genus Pistacia that produces edible nuts. It is a native of western Asia and Asia Minor, and wild representatives are still found in hot, dry locations in these areas. The pistachio was introduced to Europe at the beginning of the Christian era. The USDA plant exploration service introduced the pistachio to the U.S. in 1890. It was introduced to California in 1904 at the Plant Introduction Station in Chico, CA (Hendricks and Ferguson, 1995).
The pistachio tree is dioecious, thus orchard plantings must include the appropriate ratio of females and males (8:1 in older plantings, but up to 25:1 in more recently established orchards; Kallsen et al., 1995). At present the California industry is dominated by one male cultivar ('Peters') and one female ('Kerman'), although other cultivars are being tested. The reliance on single cultivars poses the potential for catastrophic problems for the industry with pests and diseases, and efforts to evaluate existing alternative germplasm and develop new cultivars are underway (Parfitt, 1995a,b). There is also a limited number of rootstocks in use. While the Verticillium-tolerant Pistacia integerrima is currently the dominant rootstock in use, P. atlantica x P. integerrima is increasingly being planted in California (Krueger and Ferguson, 1995). An important problem for pistachio growers is the strong tendency toward alternate bearing.