Who is the report targeted at?
Both organic and conventional producers who are interested in whether chitosan proves effective as a product for stimulation of plant defence.

Background
The term ‘plant defence booster’ applies to a group of compounds, which act by triggering various physiological and morphological responses within the plant that help to stimulate natural defence mechanisms. The practical significance of plant defence boosters is that they can help to reduce the amount of crop protection chemicals applied to crops.

Chitosan is a plant defence booster derived from deactylation of chitin. Chitin is readily available from shellfish waste from food processing. Agricultural applications of chitosan are for stimulation of plant defence. The chitosan molecule triggers a defence response within the plant, leading to the formation of physical and chemical barriers against invading pathogens.

Agricultural chitosan formulations are not readily available in Australia for trial evaluation purposes, although there are numerous Asian companies willing to ship bulk supplies to Australia. A quarantine biological import permit is required to bring chitosan into Australia. Generally, chitosan products are not well described and most manufacturers were unable to state exact concentration of chitosan in the product.

Aims/Objectives
While some chitosan efficacy studies have been completed overseas, most have investigated the biochemical and physiological plant responses to chitosan. There have been few field studies, and very limited replicated trial work conducted in Australia. The aim of this project was to screen chitosan in a number of crops to determine the potential of chitosan as a plant defence booster in Australian agriculture.

Methods used
One chitosan was sourced from China for trial work. A formulation of chitosan called Aminogro® was used in most trials. Aminogro® is the only formulation of chitosan that is produced in Australia and which is certified as an allowable organic input. Screening trials were conducted in tomatoes, peas, carrots, beetroot, lettuce, snow peas, cucumber and capsicums. No phytotoxicity was observed in any of the trials. In this project, trial results were most promising in tomatoes. Aminogro® chitosan resulted in yield increases of nearly 20% in two out of three tomato trials. In all tomato trials, chitosan applications resulted in a significant improvement in powdery mildew disease control.

Results/Key findings
Trial results and recent publications in international literature indicate Solanaceae plants may respond well to plant defence booster products. Screening of plant defence booster products in potatoes is recommended for future trial work. Solanaceae crops are significant vegetable crops in Australia, and there is a potentially large target market. Growers would have considerably more confidence in chitosan as a crop protection input if it was registered with the Australia Pesticides and Veterinary Medicines Authority (APVMA). A checklist of requirements for registration of chitosan with APVMA is included in the report.

Plant physiological studies were limited because of difficulties with enzyme activity methods. No relationships between chitosan application and stimulation of chitinase enzyme activity was identified.

Results from the literature indicate variability in detection of plant defence responses following application of plant defence boosters.

Implications for relevant stakeholders
If proven effective, chitosan has the potential to be used as a plant defence booster in both organic and conventional systems and thus could be used by all producers.

Recommendations
It is recommended that the most conclusive results about plant defence activation would be achieved with molecular studies, although this would be very expensive.
 

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