Scarification and Environmental Effects on Seed Germination in Minnesota Hardy Prunus

For Prunus seeds to germinate, deep physiological and mechanical dormancies must be overcome. Even with long periods of cold stratification, germination rates are poor in many Prunus species. In addition, very little is known about the germination requirements in winter-hardy Prunus cultivars bred for Minnesota conditions (USDA Z3-4). The objective of this study was to determine effective methods to break seed dormancy in 12 plum (P. domestica, P. americana x P. salicina), 4 tart cherry (P. cerasus) and 3 apricot (P. armeniaca) cultivars. In 2012 and 2014, open-pollinated seeds of each cultivar were collected, dried, and refrigerated prior to treatment.  For each cultivar, half of the seeds were scarified prior to planting then all seeds were subsequently warm stratified for two weeks prior to cold stratification.  Cold stratification took place either in a cooler (120 days at ~6C) or overwintered in field (average air temperature of -3.9C, range: -24.4 to 21.7C). After stratification in the cooler, pots were placed in greenhouse and seed germination was recorded weekly for 8 weeks. Pots in field were monitored for germination in situ.  Seed germination was highest in the greenhouse environment regardless of scarification. In 2012, the highest germination percentages were observed in the apricot cultivars (30-100% in greenhouse; 15-75% in field), the lowest were observed in tart cherry cultivars (<10 to 30% in greenhouse; 0 to 30% in field) and the plum cultivars were highly variable. In the greenhouse environment, germination began within the first week of removal from the cooler. Apricot cultivars showed the fastest rates of germination with a high percentage germinating within the first three weeks.