PhDThesis_LengCover.pdf (3.43 MB)
Germination issues in the cultivation of Echinacea angustifolia in Tasmania
thesisposted on 2023-05-26, 04:54 authored by Cover, SL
Echinacea angustifolia is a sought after medicinal herb originating from the Prairies of North America, however efforts to grow the species commercially have been hampered by seed dormancy. Seed pre-treatments had been successful in vitro but translation to field situations had been met with varying degrees of success. Pretreatment of seeds also carried a risk of loss because of reduced viability over the time involved with pretreatment. This study investigated the most commonly used seed pretreatments and their effects on germination of E. angustifolia under laboratory, glasshouse and field conditions. It also investigated whether the manipulation of temperature and time would reduce the pretreatment period. The field experiment examined variation in sowing times and hence the use of natural climatic conditions to eliminate the need for chemical, or other, pretreatments. Stratification or moist chilling is the most widely used method of seed pretreatment for overcoming dormancy in E. angustifolia. Six weeks of stratification in water at 4 oC increased the germination percentage of a dormant seedlot from 34% to 72%. A further improvement to 82% was obtained with stratification for two weeks in 10-3 M ethephon (2-chloroethylphosphonic acid). These pretreatments were also effective in a seedlot with low primary dormancy improving germination from 73% to 95%. In other experiments, ethephon was effective after only six to seventy-two hours at temperatures ranging from 4 oC to 25 oC. This suggested that seeds can be soaked in 10-3 M ethephon at ambient temperature for six hours on the day of sowing, therefore eliminating stratification for longer periods with associated risks. Ethephon pretreated plants, however, appeared to have slightly reduced growth under glasshouse conditions. The effectiveness of seed pretreatment was countered by other conditions in both the glasshouse and in the field. Seeds in a glasshouse trial appeared to have entered to a secondary dormancy state with 14-50% less germination than the laboratory results. These results were reflected in the field which had 33-51% less emergence. Temperature and water potential were the most likely causes of secondary dormancy. Results from experiments indicated that at 25 oC, germination and viability of seeds were affected when the water potential was -0.75 MPa or higher. This has implications in irrigation management during the early stages after spring sowings. The field experiments demonstrated the effectiveness of dormancy loss through natural field conditions of untreated seeds for the winter month of July (southern hemisphere) when there were three months of soil temperatures below 10 oC. However, spring sowings required seed pretreatments to achieve reasonable field emergence. The results are discussed in terms of practical management of this species as a commercial crop in Tasmania.
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