ADAMS, CHRISTOPHER A., JERRY M. BASKIN, AND CAROL C. BASKIN.* School of Biological Sciences, University of Kentucky, Lexington, KY 40506; School of Biological Sciences, University of Kentucky, Lexington, KY 40506; School of Biological Sciences and Department of Agronomy, University of Kentucky, Lexington, KY 40506. - Seed dormancy in the Appalachian endemic Aristolochia macrophylla Lam. (Aristolochiaceae).
The purpose of the first author's dissertation research is to compare
seed dormancy-breaking and germination requirements of the three
closely related species Aristolochia macrophylla, A. tomentosa
(eastern U.S.), and A. californica (California). However, only
results for A. macrophylla will be presented in this talk.
Aristolochia macrophylla is a deciduous, woody vine found in mesic
forests of the Appalachian Highlands Physiographic Division from
southwestern Pennsylvania south to northern Georgia. Seeds of A.
macrophylla have linear, underdeveloped embryos [1.99mm ± .08
(mean ±SE) in length] that more than double in size before they
germinate. Embryos in fresh seeds incubated at 35/20, 30/15, 25/15,
20/10, and 15/6°C in light and in dark for 90 days grew in
all regimes, but the fastest growth rate was at 25/15°C.
Highest germination percentages occurred at 25/15°C, where
47 and 39% of the seeds germinated in light and dark, respectively,
after 30 days and 70 and 45%, respectively, after 90 days.
Twenty-three percent of the seeds that did not germinate in darkness
at 25/15°C did so after they were transferred to light at
this temperature regime. Further, 59% of the seeds that failed to
germinate in light at 25/15°C did so after 12 wk of cold
stratification, resulting in 85% total germination. Thus, some
freshly-matured seeds in the population had morphological dormancy
(MD) and others a combination of MD and physiological dormancy (PD),
i.e., morphophysiological dormancy. PD was broken by cold
stratification at 5°C, but embryos did not grow at this
temperature. Fresh seeds cold stratified for 12 wk in light
germinated to 96 and 95% in light and dark, respectively, after 60
days at 25/15°C, and those cold stratified in dark
germinated to 95 and 74%, respectively. Preliminary data suggest
that the seed dormancy-breaking requirements of A. macrophylla
differ considerably from those of A. californica.
Key words: Appalachian endemic, Aristolochia, morphological dormancy, morphophysiological dormancy, seed germination, underdeveloped embryos