Rural Industries Research & Development Corporation

RIRDC Short Report:
Research Opens the Way to Improve Geraldton Waxflower Outturn

New research funded by the Rural Industries Research and Development Corporations has pointed the way to opening new, and increasing existing, marketing opportunities for Geraldton waxflower.

The research, conducted by Dr Daryl Joyce, and colleagues Alan Wearing, Melissa Taylor and David Simons at the Department of Plant Production, Gatton College, University of Queensland, has shown that use of selected pre- and post-harvest fungicides, and improved packaging and temperature management during the transport chain, can significantly improve the outturn of waxflower.

Applying these findings would improve the marketability of the waxflowers and thereby open up new and expand existing market opportunities.

The report points the way to improving the marketability of Geraldton waxflowers by highlighting integrated management strategies which can reduce unsightly fungal lesions and growth and flower fall.

Identifying the causes

The principal aim of the project was to identify the causes of flower fall in Geraldton waxflower and recommend strategies to combat this.

The report says that to prevent fungal-induced flower fall it is fundamentally important, in the first instance, to control fungal growth.

In light of this, the project focused on:

• improving the control of post-harvest pathogens;
• improving the in-package micro climate;
• determining the relative efficacy of alternative and novel fungicides, and
• use of calcium as a means of suppressing fungal growth.

Geraldton waxflower is grown throughout Australia and has been cultivated as a commercial crop for about 20 years.

In this time, flower fall (abscission) has become a major problem due to the clear abscission zones at the base of the calyx tube and pedicel.

Preliminary research suggested that this problem was caused by fungal infections as these infections lead to the flower tissue itself producing ethylene and that it is this ethylene which causes flower fall. Earlier research also discounted physical injury, water stress and exogenous ethylene, that is externally produced or sourced ethylene, as major causes of flower fall.

In investigating this problem, Dr Joyce and colleagues, collected waxflower samples from throughout Australia, including three sites in Queensland, Dareton in NSW, Mullewa in Western Australia and Alice Springs.

The fungus Alternaria alternata was found in all samples, except the sample taken from one site in Queensland. Other fungi found included Botrytis cinerea, Epicoccum, Fusarium, Deschlera, Trichoderma and Rhizopus.

The key to control

The researchers found that the key to controlling B. cinerea was to arrest the aging (senescencing) of the flower as aging flowers provided ideal conditions for fungal growth.

They also found that combining pulsing waxflower with silver thiosulphate and dipping in fungicide (eg. Rovral) before packing dry material into ventilated cartons cooled with forced air eliminated the disease. Flowers held in packages with forced air cooling holes had a vase life of over 4 days, more than twice that of the unventilated packages.

This combination, with strict temperature control in cool rooms and transport vehicles, should ensure the safe movement of waxflower from the farm to the consumer, with improved outturn quality and longer flower and foliage vaselives.

The report says that although they did not experiment with variable temperatures in these experiments it was probable that the combination of these techniques, together with an efficient cold transport chain, would most likely eliminate disease and flower and leaf fall.

Low temperature in the transport chain would also greatly help achieve longer flower and foliage vaselives.

Experiments also provided further evidence of the need to develop better carton designs that meet the specific needs of transporting waxflower.

The research found that the new designs might incorporate strategically placed extra ventilation holes to remove ethylene and to lower relative humidity immediately surrounding the flowers.

The project also examined the impact of ethylene absorbing materials on the level of disease severity. The results showed that disease severity was not reduced by placing ethylene absorbing materials in the flower cartons.

In fact, water condensed on the plastic films and created an ideal environment for growth of B. cinerea. It was also discovered that the plastic protective film over Purafil sachets created the worst problem.

These findings indicated that ethylene scrubbing materials were ineffective in commercial cartons.

Conclusions and recommendations

• Strict pre-and post-harvest hygiene to reduce fungal inoculum loads, especially of Botrytis cinerea and Alternaria alternata.
  
• Judicious pre-and post-harvest use of pesticides. For example, scheduling of regular applications, additional applications after rain, reservation of eg. Roval specifically for packing shed use and alternation of formulations.
  
• Ongoing research into and development of novel fungicides in face of known and potential development of resistance to specific fungicides by pathogens. Benomyl-resistant strains of Botrytis cinerea are found on waxflower.
  
• Maintenance of the post-harvest cold chain through handling and marketing.
  
• Treatment with STS to inhibit ethylene effects.
  
• Use of packages which provide venting to reduce relative humidity and vent away ethylene from the vicinity of the flower ‘heads’.
  
• The research found that pre- or post-harvest calcium treatments did not appear to be effective in reducing pathogen-induced flower drop in waxflower.