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Abstract

At the time this research project was initiated, the Tasmanian pyrethrum industry was
attempting to establish crops by sowing rather than by planting of 'splits' or seedling
plugs. This thesis investigated plant density and sowing times required for maximum
yield. Studies were also conducted to improve chances for successful crop establishment
from seed. That work investigated environmental requirements for germination and
aspects of seed quality and seed production.
Previous studies have examined the influence of density on yield of pyrethrins, but none
had been conducted in sown trials, in cool temperate environments, over a wide range of
plant densities. Furthermore, the influence of plant density on components of yield had
not been intensively investigated. This work identified that maximum yield was achieved
in the first season at between 16 and 39 plants/m2 and at or above 16 plants/m2 in the
second season following establishment. Yield was a function of dry flower yield rather
than due to change in percentage of pyrethrins in the flowers. Higher flower yield was
associated with greater above- ground dry matter production. The yield component
which increased with plant density was number of flowering tillers/m 2 . Yield components
decreasing with density included number of flowering tillers/plant, flowers/tiller and dry
weight/flower. Other aspects of changing plant morphology and development with
density investigated included, crop height, mean flower maturity and plant survival. The
recommendation to industry was to aim for a plant population of above 16 and below 39
plants/m2 . Yields achieved in this work were unprecedented in the pyrethrum agronomy
literature.
No reported studies have examined the influence of time of sowing on pyrethrins yield.
Field studies showed that sowings later than mid-November led to significant reductions
in yield in the first flower harvest. Yield reductions were associated with decreased dry
matter production/plant and flowering tillers/plant. Later sowings resulted in plants
failing to flower or in significant reductions in the extent of flowering. Sowing earlier
than mid-November resulted in no significant increases in yield.
As pyrethrum crops have not been traditionally established by sowing, only scant
information was available on requirements for germination, or seed quality. A field study
and three laboratory trials investigated the influence of temperature and seed quality on
germination and emergence. Results demonstrated that rate and final emergence varied
significantly at different times of year. In general, the proportion of viable seed sown that
emerged and survived was very low. Both rate of emergence and final emergence percentage were associated with temperature. Laboratory investigation of germination
percentage, rate and uniformity of germination of a seed lot under a range of constant
temperatures confirmed the previously reported findings relating to germination
characteristics of this temperate species. Unexpected though was the high proportion of
dead seed found at temperatures only several degrees higher than the temperature for
optimal germination rate. Six seed lots were subsequently germinated at low, medium
and high temperatures which provided some insight into the seed death phenomenon as
well as documenting the range of behaviours from different seed lots. An explanation for
differences in germination behaviour involving seed maturity was proposed for different
seed lots and this was tested in a subsequent study. Finally, the effects of an 18 month
storage period on the germination characteristics seed lots was investigated in a
laboratory trial. There was little change in most germination parameters except for time
to complete germination which increased in all seed lots after storage and uniformity of
germination which decreased. Changes were assumed to be due to satisfaction of an
after ripening requirement.
Laboratory studies investigated the influence of seed mass on various germination and
seedling development characteristics. Variation in seed mass within seed lots was
identified but this had little impact on rate of germination or other germination
parameters. However, a following, study revealed that heavier seedlings emerged from
seeds that germinated earliest within seed lots. Furthermore, heavier seedlings
demonstrated faster development than did lighter seedlings. Although seedling mass was
found to be associated with rate of germination within seed lots, this factor failed • to
explain significant differences in mean time to germinate between seed lots. It was
subsequently recommended to industry that cleaning on a size or mass basis could
improve seed quality. The influence of harvest date on seed quality and quantity were investigated. Results
indicated that losses of larger achenes from the harvested flowers were occurring with
lateness of harvest. Characteristics of the seed including mean seed mass, proportion of
viable seed in the sample, germination percentage and rate of germination were found to
vary considerably with harvest date. Data generated in this work were found to be
consistent with the model which proposed that variability in germination parameters was
due largely due to maturity of seed at harvest. A following study revealed that relative
position on the capitulum also had a profound influence on germination parameters of the
seed. The recommendation for industry emanating from the harvest date work was that
flowers should be cut at a field capitulum moisture of 25%.
Finally, variation in seed quality and quantity was evaluated both within and between
capitula. This study revealed that small flower heads produced fewer and smaller seed
than larger heads. Outer achenes, regardless of whether they came from large or small
capitula were found to germinate more rapidly than inner achenes. Peripheral achenes
weighed more than central achenes and gave rise to heavier seedlings.
The methods and results in this study will serve as a valuable source of information for
agronomists and plant breeders working on improvement of pyrethrum production. The
investigations on seed quality and seed production provide a sound base for future efforts
to improve seed quality and crop establishment. The findings presented provide the
Tasmanian pyrethrum industry with critical information with respect to target plant
densities, sowing times, seed quality and seed production. It is expected that
implementation of findings from the study will prove to be pivotal in continued industry
profitability and expansion.

Item Type:	Thesis - PhD
Authors/Creators:	Fulton, David
Keywords:	Pyrethrum (Plant), Pyrethrum (Plant)
Copyright Holders:	The Author
Copyright Information:	Copyright 1998 the Author - The University is continuing to endeavour to trace the copyright owner(s) and in the meantime this item has been reproduced here in good faith. We would be pleased to hear from the copyright owner(s).
Additional Information:	Includes bibliographical references. Thesis (Ph.D.)--University of Tasmania, 1999
Item Statistics:	View statistics for this item

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