Pretreatment Effects on Seed Germination of Two Nyssa Species

The genus Nyssa L. includes several woody species with traits valued by horticulturists, but only black gum (Nyssa sylvatica Marsh.) is prevalent in the nursery trade. A congener, swamp tupelo (Nyssa biflora Walt.), might be a marketable shade tree, but little is known about propagating it from seeds. Because cold, moist stratification overcomes embryo dormancies of black gum, we compared germination of cleaned seeds (surrounding pulp of fruits removed) of swamp tupelo and black gum that were stratified at 5 degrees C for 0, 14, 28, 42, 56, 70, 84, and 112 days. Seeds of swamp tupelo within intact drupes were also stratified. Across all durations of stratification, 79% of cleaned seeds of swamp tupelo germinated, whereas 11% of seeds within drupes germinated. Germination value of cleaned seeds of swamp tupelo increased from 1.26 to 3.23 as duration of stratification increased. Although cleaned seeds of black gum responded similarly, the benefit of stratification was more pronounced, and the mean germination percentage was lower than for swamp tupelo (66% vs. 79%). In a second experiment, irrigation with low and high concentrations of an extract of fruit pulp of swamp tupelo reduced germination of seeds of basil (Ocimum basilicum L. 'Superbo'), spinach (Spinacea oleracea L. 'Bloomsdale'), zinnia (Zinnia xmarylandica Spooner, Stimart, and Boyle 'Double Zahara Cherry'), and swamp tupelo by 25% to 63% (low concentration) and 40% to 70% (high concentration). Propagators should remove the surrounding pulp from seeds of swamp tupelo and cold stratify them at least for 4 weeks.