Mimulus gemmiparus as a model for the ex situ propagation and study of propagule storage for a species of concern
Date
2017
Authors
Harden, Dyan, author
Klett, Jim, advisor
Steingraeber, David, committee member
Qian, Yaling, committee member
Journal Title
Journal ISSN
Volume Title
Abstract
Mimulus gemmiparus, W.A. Weber, budding monkeyflower, is a Colorado narrow endemic plant that could be at risk of extinction. Factors including rarity, a unique mode of clonal, vegetative, annual reproduction through petiole enclosed brood bulbils, specific microhabitat requirements, limited means of dispersal for migration, and vulnerability to stochastic events all play roles in M. gemmiparus survival. Conservation efforts by researchers and federal and state land managers have involved passive protection of existing known populations and active measures such as assisted establishment. A decision matrix to prioritize the active propagation of Colorado species of concern is presented that identifies M. gemmiparus as a high priority for action. Ex situ propagation from field collected M. gemmiparus propagules can provide large quantities of plant material for active conservation efforts, however, short term to long term storage parameters for propagules have not been empirically investigated. Propagation of M. gemmiparus was undertaken in order to multiply propagules to produce material for a cold storage experiment to support active conservation efforts, also in order to document a reliable, repeatable propagation method that can be used to create banks of plant and propagule material for conservation, propagation, restoration, research, and storage. Interactions between water, temperature, and desiccation tolerance characteristics of the vegetatively reproductive bulbil are key to determining optimal storage conditions. Categories of seed storage behavior, orthodox, recalcitrant, and intermediate, differentiated by seed characteristics such as desiccation and cold tolerance, were used as a basis for exploration of bulbil storage behavior. The basis of knowledge used to guide cold storage of multiplied propagules was built on viability assays, measurements of bulbil moisture content, and storage temperature exposure and duration response. An empirical study examined bulbil post storage temperature exposure germination response in 4 MIGE ex situ propagated populations at temperatures -20⁰, -3⁰ to 0⁰, and 3⁰ to 5⁰C for 24 hours, 1 month, 3 months, and 6 months compared to a control storage temperature of 20⁰C. Bulbil viability at moisture contents below 0.1 gH2Og-1DW, and longevity at subfreezing temperatures did not conform to typical orthodox or recalcitrant seed behavior. Propagules with a mean moisture content of 0.3877 gH20g-1DW stored for 6 months at 3⁰ to 5⁰C retained the highest rates of post storage temperature exposure germination observed over 12 weeks. A low moisture content threshold where germination observed over 12 weeks was ≤10% was found between 0.1350 and 0.1817 gH20g-1DW. There was not a higher post exposure germination response in low moisture content bulbils stored at subfreezing temperatures compared to high moisture content bulbils exposed to subfreezing temperatures. Storage behavior appeared intermediate in nature. Further study could confirm that the 3 to 5 year longevity at 5⁰C storage temperature potential predicted for intermediate seeds is applicable to MIGE bulbils. M. gemmiparus serves as a model that demonstrates the feasibility and efficacy of ex situ propagation and propagule storage for a species of concern. Creation and management of ex situ plant and propagule banks are intended as a compliment to, not a replacement for, traditional conservation of in situ populations. More study is needed using more controlled methods of desiccation or specialized pre treatments such as the application of cryoprotectants to bulbils or meristematic tissue to preserve germplasm for longer time frames at freezing temperatures.