Pretreatment Effects on Seed Germination: An Interspecific Comparison of Two Nyssa Species

The genus Nyssa Gronov. ex L. includes several woody species with traits valued by horticulturists, but only Nyssa sylvatica Marsh. (black gum) is prevalent in the nursery trade.  Although we hypothesize that a closely related species, Nyssa biflora Walt. (swamp tupelo), can be a useful tree for managed landscapes, little is known about propagating it from seeds.  Embryos of Nyssa display moderate dormancies that may be overcome with cold, moist stratification.  Fruits of Nyssa biflora were collected in 2013 from indigenous trees at two sites in Virginia and one site in North Carolina; fruits of Nyssa sylvatica were collected from trees at the Minnesota Landscape Arboretum.  We compared germination of seeds (depulped drupes) of Nyssa biflora and Nyssa sylvatica, and whole fruits (intact drupes) of Nyssa biflora after stratification at 5°C for up to 112 days.  Germination value of Nyssa biflora was as high as 0.60 for seeds stratified for six weeks, compared to non-stratified seeds that showed a germination value of 0.25.  Germination percentage of Nyssa biflora was not affected by duration of stratification.  Germination percentage of non-stratified seeds of Nyssa sylvatica was 1%, and germination increased only slightly after 14 days of stratification, increased more after 28 days, and was as high as 85% after 42 days of stratification.  We conclude that seeds of Nyssa biflora are less resistant to germination than are seeds of Nyssa sylvatica.  Mean germination percentage of Nyssa biflora over 0, 14, 28, and 42 days of stratification was 9.6% with pulp intact and 77.6% with pulp removed.  We postulate that the pulp may contain germination inhibitors and recommend that propagators remove pulp before sowing seeds of Nyssa biflora.