Jujubes (Ziziphus jujuba Mill.), also called chinese dates, belong to the Rhamnaceae family. Jujube cultivars were first imported into the United States by U.S. Department of Agriculture (USDA) agricultural explorer Frank N. Meyer from 1908 to 1918 (Meyer, 1911; Thomas, 1924; Yao, 2013). In the past hundred years, jujubes were cultivated mainly in the southwest, southern, and southeastern states from North Carolina, South Carolina to Florida, and from Florida and Georgia all the way to California; but they had been reportedly grown as far north as Pennsylvania (Ashton, 2006, 2008; Atkins, 1987; Locke, 1948, 1955; Lyrene, 1979, 1983; Yao, 2013). Recently, we noticed some jujube trees along the historic Chinese railroads or mine worker campsites in the southwest (Yao, 2015). Dry jujubes were part of those Chinese workers’ diet and the littered seeds left behind grew voluntarily. Local people did not know much about jujubes but kept the trees that produced large and good-tasting fruit. These volunteer seedling plants belong to Z. jujuba and could be good germplasm for new cultivar selections.
Early researchers had identified that jujube grew and produced well and had great potential in the southwestern United States (Fairchild, 1918; Hager and Edward, 1989; Lanham, 1926; Locke, 1948, 1955; Meyer, 1916; Sweet, 1985). Because of various reasons, however, jujube production is still limited. Recently, interest in jujubes from growers and consumers is surging, and nurseries have had a hard time meeting the market demand (Ron Ludekens, personal communication). The challenges now are very limited commercially available cultivars and research support. Growers are frustrated due to insufficient information on cultivars, cultural management, processing, and marketing.
There are over 800 jujube cultivars known in China (Guo and Shan, 2010; Liu, 2008) while there are only a few cultivars commercially available in the United States with ‘Li’ and ‘Lang’ as the two most dominant. All jujube growers request more cultivars to extend the fruit supply season and to be used for different purposes to meet the consumers’ demand (Yao, 2013).
Unlike apple or peach, jujube flowers are not initiated the previous year but the same year as they bloom. As the flexible deciduous fruiting structure—branchlets grow, they initiate flowers (Yao, 2012a). Jujubes have tiny flowers of ≈6 mm in diameter and have many more flowers than most fruit crops (Guo and Shan, 2010; Liu, 2006; Yao, 2012a). Each branchlet can have from 20 to over 100 flowers depending on the cultivar. Branchlet growth, flower initiation, blooming, fruit setting, and fruitlet growth occur simultaneously. Because of the high nutrient competition, jujubes, in general, have low fruit set (Guo and Shan, 2010).
In the 1950s, the USDA Chico Plant Introduction Station had a jujube breeding program for some years; unfortunately, the Chico Station was closed in the late 1950s. During their jujube breeding/cultivar selection process, they mentioned the need for a complete understanding of flowering, pollination, self-sterility, and seed development and conducted some preliminary research on these topics (Ackerman, 1961). Yan et al. (2009, 2010) reported the fruiting characteristics of more than 100 Chinese cultivars. In the United States, the flowering and fruiting habits of existing cultivars and new importations are largely unknown, and this fundamental knowledge would be critical for jujube breeders and researchers. Extension personnel and growers also need this information for cultivar recommendations or cultivar selections.
The New Mexico State University (NMSU) Sustainable Agriculture Science Center at Alcalde, New Mexico, has imported 30+ jujube cultivars from China and collected a number of cultivars in the United States for a total of over 50 cultivars. The objective of this study is to examine the blooming types, flowering characteristics, self-pollination/self-fertility, and seed development of these cultivars.
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