Pomegranate [Punica granatum L. (Lythraceae)] is believed to have originated in the southern Caspian region and northeastern Turkey, and the Mediterranean Basin is an important diversification center of the species (Halilova and Yildiz, 2009; Levin, 1994). Today, it is extensively cultivated in Afghanistan, Egypt, Italy, India, China, United States, Chile, Spain, and Turkey (Stover and Mercure, 2007), and in Turkey in the Mediterranean, Aegean, and southeastern Anatolia regions (Ercisli, 2004; Ozgen et al., 2008). Pomegranate was introduced to China 2000 years ago, and famous production areas include Lintong in Shanxi Province, Zaozhuang in Shandong Province, Huaiyuan in Anhui Province, Huili in Sichuan Province, Mengzi in Yunnan Province, and Kashgar in Xinjiang Province (Wang et al., 2010).
Although some crop species can be propagated vegetatively, development of new cultivars depends on the plant breeder being able to produce plants from seeds. Pomegranate is a shrub or a small tree widely planted in both tropical and subtropical areas (Wang et al., 2013). Its roots, bark, fruit juice, and dried fruit peel contain abundant anthocyanins and/or hydrolysable tannins that have strong antioxidant (Chidambara et al., 2002), antitumor (Afaq et al., 2005; Hora et al., 2003), and hypolipidemia (Huang et al., 2005) activities. In China, pomegranate is an important crop in six provinces, with about 238 cultivars (Feng and Chen, 2000). However, there are widespread problems with pomegranate cultivars, including poor quality and low yield, which greatly limit the development of the pomegranate industry (Gulimire et al., 2003). Thus, improvement of old cultivars and development of new ones are of great significance (Mars, 2000).
The purpose of our study was to gain a better understanding of the dormancy breaking and germination requirements of pomegranate seeds to facilitate growing genetically diverse plants for selection of new cultivars. Previous studies have shown that cold stratification, soaking, or both in concentrated H2SO4 can increase the germination percentage of seeds of this species (Gokturk et al., 2012; Olmez et al., 2007; Piotto et al., 2003; Rawat et al., 2010; Riley, 1981; Yucedag and Gultekin, 2009). However, no studies have been conducted on seed dormancy and germination of cultivars that grow in the cold desert region of Xinjiang Province in northwest China. Cultivation of pomegranate is concentrated in southern Xinjiang, particularly in Kashgar, Hotan, and Turpan (Gulimire et al., 2003). Four cultivars were chosen from these three production areas, based on volume of sales and popularity among the people, as our study material. We tested the effects of afterripening in dry storage at room temperature and at 4 °C, sulfuric acid scarification, treatment with gibberellic acid (GA3), cold (moist) stratification, acid scarification plus cold stratification, and warm stratification followed by cold stratification on breaking seed dormancy in the four Xinjiang cultivars Kashgar Akeqishiliu (I), Yecheng Suanshiliu (II), Hotan CeLe1#shiliu (III), and Turpan Suanshiliu (IV) from Kashgar, Kashgar, Hotan, and Turpan, respectively.
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