Research Publication Title

Germination in Milkweeds (Asclepias, Apocynaceae): Response To Cold Stratification And Moisture Pretreatment

Major

Biology

Faculty Mentor(s)

Dr. G. Ionta

Keywords

Germination, Milkweed, Cold Stratification, Asclepias, Monarch

Abstract

The North American population of the monarch butterfly (Danaus plexippus) has experienced a significant decline in the past two decades. This shrinkage follows a concurrent reduction in the availability of larval host plants such as milkweed (Asclepias species), due to recent agricultural practices. Accordingly, the reintroduction of milkweed into habitats accessible to monarch populations is a high priority for monarch restoration efforts. Milkweed seed, however, has an inherent dormancy, requiring exposure to a period of cold temperatures (e.g. winter conditions) before germination can take place. The ability to readily prepare seeds for planting independent of seasonal constraints would therefore provide a resource and timesaving shortcut to restoration efforts. We set out to determine optimal cold and moisture treatments for breaking seed dormancy in three milkweed species, Asclepias syrica, A. tuberosa, and A. incarnata, by subjecting them to varying periods of cold stratification and moisture pretreatment prior to incubation, and recording subsequent germination rates. The seeds underwent stratification at 0°C for either 7, 14, 21 or 28 days, followed by incubation in a growth chamber at alternating 16:8 hour temperature regimes of 27°C and 20°C, simulating natural ecological conditions. Half of the seeds were moistened before stratification, while the other half remained dry. Germination was determined by the appearance of a radical longer than 0.5mm in length, and time to germination and overall germination rates were recorded for each treatment. Unexpectedly, our results showed no statistically significant difference in germination rates as dependent on days stratified, but revealed a significant difference in germination rates based on moisture pretreatment, with a higher mean germination rate for un-moistened seeds at 0.80 +/- 0.068, compared to moistened seeds at 0.57 +/- 0.052.

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Germination in Milkweeds (Asclepias, Apocynaceae): Response To Cold Stratification And Moisture Pretreatment

The North American population of the monarch butterfly (Danaus plexippus) has experienced a significant decline in the past two decades. This shrinkage follows a concurrent reduction in the availability of larval host plants such as milkweed (Asclepias species), due to recent agricultural practices. Accordingly, the reintroduction of milkweed into habitats accessible to monarch populations is a high priority for monarch restoration efforts. Milkweed seed, however, has an inherent dormancy, requiring exposure to a period of cold temperatures (e.g. winter conditions) before germination can take place. The ability to readily prepare seeds for planting independent of seasonal constraints would therefore provide a resource and timesaving shortcut to restoration efforts. We set out to determine optimal cold and moisture treatments for breaking seed dormancy in three milkweed species, Asclepias syrica, A. tuberosa, and A. incarnata, by subjecting them to varying periods of cold stratification and moisture pretreatment prior to incubation, and recording subsequent germination rates. The seeds underwent stratification at 0°C for either 7, 14, 21 or 28 days, followed by incubation in a growth chamber at alternating 16:8 hour temperature regimes of 27°C and 20°C, simulating natural ecological conditions. Half of the seeds were moistened before stratification, while the other half remained dry. Germination was determined by the appearance of a radical longer than 0.5mm in length, and time to germination and overall germination rates were recorded for each treatment. Unexpectedly, our results showed no statistically significant difference in germination rates as dependent on days stratified, but revealed a significant difference in germination rates based on moisture pretreatment, with a higher mean germination rate for un-moistened seeds at 0.80 +/- 0.068, compared to moistened seeds at 0.57 +/- 0.052.