Influence of Seed Size, Testa Color, Scarification Method, and Immersion in Cool or Hot Water on Germination of Baptisia australis (L.) R. Br. Seeds

A series of experiments was performed to examine the germination responses of Baptisia australis (L.) R. Br. seeds. Germination tests were conducted at 23 °C and numbers of germinated seed were counted daily for 21 days. Seeds were separated into two size fractions using standard sieves. Seeds in the large-seeded fraction were heavier than those in the small-seeded fraction, but seed size/weight did not affect the germination percentage at 21 days (G21), the number of days to 50% of final germination (T 50 ), or the number of days between 10% and 90% germination (T 90 – T 10 ). Seeds were classified into two groups based on testa color. Light-brown seeds (17% of total) were heavier and had lower G21 and higher T 50 and T 90 – T 10 values than medium- to dark-brown seeds (83% of total). Seeds scarified mechanically germinated nearly 100% and had lower T 50 and T 90 – T 10 values than untreated seeds. Untreated seeds had a higher T 50 value than seeds soaked overnight in 20°C water, but the G21 and T 90 -T 10 values were similar for the two treatments. Mechanical scarification followed by overnight soaking in 20 °C water yielded a G21 value of only 12%, and the low germination percentage was attributed to imbibition damage. When seeds were scarified in concentrated H 2 SO 4 for 0, 1, 5, 20, 40, or 80 min, G21 values increased quadratically while T 50 and T 90 – T 10 values decreased quadratically as the immersion time increased. To test the effects of moist heat on germination responses, seeds were immersed for 0, 0.5, 1, 2, 4, or 8 minutes in 85 °C water. G21 values increased linearly as the immersion period increased from 0 to 2 min but remained similar when the immersion time exceeded 2 min. The duration of immersion in hot water did not affect the T 50 values whereas T 90 – T 10 values decreased linearly as the immersion period increased. We conclude that physical dormancy is responsible for temporal variation in germination of B. australis seeds. Scarifying seed in concentrated H 2 SO 4 for 20 to 80 minutes may be the most practical means of treating bulk lots of B. australis seeds to obtain rapid and uniform (≥85%) germination.