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Biological limitations to the production of processed broccoli in Tasmania

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Boersma, M (2009) Biological limitations to the production of processed broccoli in Tasmania. PhD thesis, University of Tasmania.

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Abstract

An increased pressure from international competitors on the domestic production
of processed broccoli has meant that this sector needs to identify ways in which it
can reduce the cost of raw produce supplied to local processors. This is best
achieved through improvements in net yield and efficiencies that reduce labour
costs. This thesis addresses three biological impediments to achieving
improvements in these areas: Uneven harvest maturity resulting in numerous
harvests; processing inefficiencies introduced by inappropriate head shape; and
reduced quality from hollow stems.
Investigations undertaken during the course of this work have found that the
variation in the meristem diameter during inflorescence initiation explains 50% of
the variation in maturity encountered at harvest. This finding highlights the
importance of introducing and maintaining seedling uniformity during the
transplant and establishment phases of production to minimise variation in
maturity at harvest, thus reducing harvest costs. It also provides a basis for future
research to focus on techniques to achieve this outcome. The study has also demonstrated the influence of head shape on processing
efficiency and net yield. The more compact shape of 'Shamrock' resulted in a
superior (low) ratio of the less valuable stem tissue to the more valuable floral
tissue when compared to the elongated form associated with 'Marathon'. The
architecture of the 'Shamrock' inflorescence also provided higher total floret yield,
and more opportunity to manipulate the levels of stem material to suit seasonal
requirements. The attributes associated with 'Marathon' resulted in greater
processing efficiency, with the comparatively open branch structure of this variety
producing more segments within factory specification, and a smaller proportion
that required re-dicing. These findings establish the significant impact of head
shape on net yield and processing efficiency, providing an additional tool to
improve these through varietal selection.
Since the early 1930's the development of hollow stems in broccoli and cauliflower
has been variously attributed to boron deficiency or to factors associated with
plant growth rates. The data presented in this study provides evidence that the development of hollow stem in broccoli is related to growth rate when
manipulated by planting density. Evidence is also provided to show that
mechanical tissue stresses generated in the stem during inflorescence
development can lead to the development of stem fractures. Tissue extensibility
tests revealed higher levels of radial, tangential and longitudinal extensibility in
the outer pith and vascular / cortex tissues, while the central pith tissues were less
extensible in all dimensions. Circumferential tension in the transverse plane was
also found to be stored in the vascular cortex region. It is proposed that the
differential mechanical properties and capacities for growth across the stem
tissues may cause sufficient internal strain to cause the fracture of the less
extensible and possibly weaker tissue of the central pith.
The findings of this thesis have established a fundamental understanding of the
physiological mechanism underlying the development of hollow stem, the
importance of the transplant and establishment phases of production on head
uniformity, and the significant influence of head shape on net yield and processing
efficiency. Application of this knowledge by the Tasmanian broccoli processing
industry will assist in improvements in net yield and provide opportunities for
efficiencies that reduce labour costs.

Item Type: Thesis (PhD)
Copyright Holders: The Author
Copyright Information:

Copyright 2009 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:

Available for use in the Library and copying in accordance with the Copyright Act 1968, as amended. Thesis (PhD)--University of Tasmania, 2009. Includes bibliographical references

Date Deposited: 25 Nov 2014 00:57
Last Modified: 07 Dec 2016 00:06
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