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An investigation of breeding methods applicable to Tasmanian-grown pyrethrum


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Groom, KL 2003 , 'An investigation of breeding methods applicable to Tasmanian-grown pyrethrum', PhD thesis, University of Tasmania.

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Pyrethrum is a perennial daisy that is predominantly out-crossed. It is
grown commercially in Tasmania for pyrethrins, which are extracted from the
flowers and are used in the preparation of insecticides. A pyrethrum breeding
program was conducted by the University of Tasmania from 1978 to 1998, with
the aim of developing varieties suitable for Tasmanian growing and production
systems. The primary selection character was pyrethrins yield, and the program
consisted of population improvement through recurrent selection for two
indirect selection characters; visually-estimated flower yield and the UV-assay of
pyrethrins at a specific maturity stage (open but not over-blown). Varieties,
consisting of either clones or single crosses between two clones, were selected
from each successive recurrent selection generation.
This study was undertaken to evaluate the selection methods used for the
University's breeding program from the period of 1985 to 1998, and to assess the
impact on breeding methods of the change in the mid-1990's from the
establishment of the crop by clonal splits planted at a contant spacing (0.5 m) to
establishment by direct-drilling at a somewhat higher average plant density.
Data records for the two main selection characters were analysed in order to
identify genetic changes in the breeding population. This indicated that there
had been a genetic gain in UV-assays but not in flower yield.
The efficiency of direct selection for first year yields in the Univeristy's base
population was compared with indices of the indirect selection characters and
yield components. A trial was established to obtain estimates of genetic
parameters to construct selection indices and predict selection responses.
Estimated heritability was moderate for pyrethrins yeld (0.26-0.39) and for the
yield components of pyrethrins content (0.24-0.34) and flower yield (0.17-0.30),
and low for percent dry matter content (0.00-0.15). Estimates were also obtained for two product quality characters, both derived from the ratio of the six different
esters that form the active product in the pyrethrum extract. Heritability for
these character was moderate to high. The effect of planting density on selection
for pyrethrins yield was also investigated.
The index of the two indirect selection characters was the most efficient
method for single-plant selection in the planting densities used commercially
from 1980 to 1995. However, an index of component characters was more
efficient for the densities currently used in commercial areas. There was
evidence for a genotype-density interaction for flower and pyrethrins yield but
not for percentage pyrethrins or the ratios of pyrethrins esters.
The potential to reduce the length of the period of obligate vegetative
growth through breeding was also assessed. There was evidence for significant
level of additive genetic control for this character and it was concluded that the
vegetative period could be reduced by recurrent selection. The performance of
new synthetic varieties were evaluated and the relative merits of varieties
derived from a single cross of two clones and polycross of several clones were

Item Type: Thesis - PhD
Authors/Creators:Groom, KL
Keywords: Pyrethrum (Plant), Pyrethins, Pyrethrum (Insecticide), Pyrethrum industry
Copyright Holders: The Author
Copyright Information:

Copyright 2003 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:

For consultation only. No loan or photocopying permitted until August 2005. Thesis (Ph.D.)--University of Tasmania, 2003. Includes bibliographical references

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