The seed, commonly thought of as a nut, is a culinary nut, not a botanical nut. The fruit has a hard, cream-colored exterior shell. The seed has a mauve-colored skin and light green flesh, with a distinctive flavor. When the fruit ripens, the shell changes from green to an autumnal yellow/red and abruptly splits partly open. This is known as dehiscence, and happens with an audible pop. The splitting open is a trait that has been selected by humans. Commercial cultivars vary in how consistently they split open. Each mature pistachio tree averages around of seeds, or around 50,000, every two years. Cultivation The pistachio tree may live up to 300 years. The trees are planted in orchards, and take around 7 to 10 years to reach significant production. Production is alternate-bearing or biennial-bearing, meaning the harvest is heavier in alternate years. Peak production is reached around 20 years. Trees are usually pruned to size to make the harvest easier. One male tree produces enough pollen for 8 to 12 drupe-bearing females. Harvesting in the United States and in Greece is often accomplished using equipment to shake the drupes off the tree. After hulling and drying, pistachios are sorted according to open-mouth and closed-mouth shells, then roasted or processed by special machines to produce pistachio kernels. In California, almost all female pistachio trees are the 'Kerman' cultivar, from Kerman, Iran. A scion from a mature female 'Kerman' is grafted onto a one-year-old rootstock. Diseases and environment Pistachio trees are vulnerable to numerous diseases and infestation by insects such as Leptoglossus clypealis in North America. Among these is infection by the fungus Botryosphaeria, which causes panicle and shoot blight (symptoms include death of the flowers and young shoots), and can damage entire pistachio orchards. In 2004, the rapidly growing pistachio industry in California was threatened by panicle and shoot blight first discovered in 1984. In 2011, anthracnose fungus caused a sudden 50% loss in the Australian pistachio harvest. Several years of severe drought in Iran around 2008 to 2015 caused significant declines in production. Production In 2020, global production of pistachios was about , with the United States and Turkey as leading producers, together accounting for 68% of the total (table). Secondary producers were Iran, China, and Syria. A 2020 report indicated that nearly half of the global production of pistachios in 2019 came from the United States, with production in