‘Thompson Seedless’ is the dominant raisin variety grown in California because of its high productivity, wide soil adaptability, seedless fruit, and versatility for use in different grape and raisin

grown in California because of its high productivity, wide soil adaptability, seedless fruit, and versatility for use in different grape and raisin products. About 95 percent of California raisins are currently produced from ‘Thompson Seedless’ grapes, followed by ‘Fiesta’ (3 percent) and ‘Zante Currant’ (1.5 percent). The remainder are produced from ‘DOVine,’ ‘Muscat of Alexandria,’ “Sultana” (false ‘Sultanina’), ‘Monukka,’ ‘Ruby Seedless,’ ‘Flame Seedless,’ and ‘Perlette.’ ‘Thompson Seedless’ is also dominant in most commercial raisin-producing countries worldwide. ‘Thompson Seedless’ has not always been the foremost raisin variety in California plantings. ‘Muscat of Alexandria’ was the first raisin variety introduced into California, and it dominated for about 40 years until the early 1920s. In 1913, about 75 percent of California’s raisins were ‘Muscat of Alexandria’ and only 14 percent were ‘Thompson Seedless.’ By 1925 the positions of the two varieties was reversed, with ‘Thompson Seedless’ constituting 80 percent and ‘Muscat of Alexandria’ 15 percent of California raisin production. This shift was in response to a rapidly growing preference for seedless raisins. Historically, the raisin industry has relied almost entirely on Old World grape varieties. There was little interest in the development of new varieties until the breeding and introduction of ‘Fiesta’ by John Weinberger of the USDA Agricultural Research Service in 1973. The principal advantage of ‘Fiesta’ is that it typically ripens about 10 to 14 days ahead of ‘Thompson Seedless’ and has high-quality, meaty raisins. Its early ripening allows growers to begin harvesting earlier, and that reduces the risk of damage from early rainfall and extends the picking period for farm laborers. New plantings of ‘Fiesta’ were interrupted for a few years after the variety was introduced, due to concerns over the presence of seed traces in the berries. The perceived seed trace problem has since waned; ‘Fiesta’ raisins are now widely accepted by raisin packers and the variety has gradually grown in importance. Interest in new varieties has increased as a result of the acceptability of ‘Fiesta’ and the recognized need for earlier-ripening, high-quality varieties. Seedlessness (seed traces of ‘Thompson Seedless’ size or smaller), early ripening, potential for drying on the vine (DOV), suitability for mechanized pruning or harvesting operations, and tolerance to important pests and diseases are other characteristics of interest to developers of new raisin varieties. ‘DOVine’ was introduced by USDA in 1995 because of its suitability for DOV with cane cutting. Its early ripening, adaptability for cane pruning, and high raisin quality characteristics give ‘DOVine’ the potential for earlier cane cutting for DOV with improved raisin quality. The future development of new varieties has the potential to revolutionize raisin production, drying, and harvesting practices.