332 BREAKING DORMANCY OF MAHALEB Al-Absi, K.M. (2010), Seed Sci. & Technol., 38, 332-340 The effects of different pre-sowing seed treatments on breaking the dormancy of mahaleb cherries, Prunus mahaleb L. seeds K.M. AL-ABSI Plant Production Department, Faculty of Agriculture, Mu’tah University, P.O. Box 7, 61710, Al-Karak, Jordan (E-mail: absikhal@mutah.edu.jo) (Accepted August 2009) Summary Seeds of the mahaleb cherry, Prunus mahaleb L., used as a rootstock in cherry production, germinate and emerge poorly due to seed dormancy. A greenhouse experiment was done to determine the effects of several treatments to overcome this dormancy, i.e. prolonged (30, 60 and 90 days) stratification followed by hot water treatment at 90°C (for 0, 10, 20 and 30 minutes) or sulfuric acid scarification (0, 10, 20 and 30 minutes) or gibberellic acid, GA 3 (0, 500, 1000 and 2000 ppm). The results showed that stratification for 60 days or more increased germination percentage and decreased mean germination time. Scarification with either hot water or sulfuric acid only improved germination percentage and speed if followed by 60 days of stratification. Treating the seeds with GA 3 resulted in a significantly higher germination rate. The highest germination percentages were attained by treating seeds which had been stratified for 60 and 90 day-periods with GA 3 at 1000 ppm. It is recommended that GA 3 should be used in addition to cold stratification for improving germination percentage and speed of mahaleb cherry seeds. Introduction The Mahaleb cherry (Prunus mahaleb L.), a member of the family Rosaceae, has been identified in Jordan as one of the most important rootstocks commonly used worldwide for sour and sweet cherries (Hrotko and Magyar, 2004). It is used as a preferred rootstock for calcareous soils and arid areas (Buman, 1977; Giorgio and Standardi, 1993). Prunus mahaleb is highly drought-resistant and produces well-anchored, sturdy trees. It is preferred for use as a rootstock because of its resistance to pests, early yield and high crop load (Cochran et al., 1961). The most common methods of cherry propagation are grafting and budding, where mahaleb or mazard cherries are the usual rootstocks used. However, seed propagation is difficult because of low germination percentages resulting from seed dormancy. Seed primary dormancy is an intrinsic inhibition of early germination in freshly harvested mature seeds. It can rely on morphological, physical or physiological factors (Baskin and Baskin, 2004). Seed germination is influenced by internal factors controlling dormancy, including seed coat factors and phytohormones (Hartman, 1997). Therefore, promoting the germination of mahaleb cherry seeds is important in propagation, breeding programs and the use of germplasms. Various methods are used to overcome seed dormancy