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

Abstract

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 (T50), or the number of days between 10% and 90% germination (T90 – T10). Seeds were classified into two groups based on testa color. Light-brown seeds (17% of total) were heavier and had lower G21 and higher T50 and T90 – T10 values than medium- to dark-brown seeds (83% of total). Seeds scarified mechanically germinated nearly 100% and had lower T50 and T90 – T10 values than untreated seeds. Untreated seeds had a higher T50 value than seeds soaked overnight in 20°C water, but the G21 and T90-T10 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 H2SO4 for 0, 1, 5, 20, 40, or 80 min, G21 values increased quadratically while T50 and T90 – T10 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 T50 values whereas T90 – T10 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 H2SO4 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.