Induction of peroxidase in Kauri (Agathis australis) by hormone treatment
Kauri dieback is a deadly kauri disease caused by a pathogen, Phytophthora taxon Agathis (PTA). PTA is an exotic pathogen in New Zealand and is capable of killing kauris of all ages. There is no known treatment or control tools available to manage this disease to date. Hormone induced plant resistance may give some protection to the plant against the pathogen. The objective of this research was to develop a hormone treatment option for the kauri dieback disease by monitoring the effectiveness of the dose response relationship of various plant hormones against the induction of the defensive protein, peroxidase in kauri. Two new methods were developed for the protein extraction and enzyme assay with special reference to the peroxidase enzyme from the kauri leaf tissue. These were the first known methods of this kind specifically for the kauri peroxidase enzyme. Optimization of the hormone doses, and the assessment of the time frame were carried out for the maximum quantisation of the target enzyme. Foliar application of different plant hormones were carried out on individual kauri trees under laboratory conditions, and changes in the activity levels of peroxidase enzyme were measured. The trees were individually treated with different plant hormones of methyl jasmonate, ethephon, β-amino-butyric acid (BABA), salicylic acid and a combination of methyl jasmonate and ethephon and the responses of peroxidase enzyme were observed in three day intervals with a time span of 18 days. A blank treated control was also carried out in a similar way. The individual hormone applications made an impact on the induction of the peroxidase activity in kauri trees, the increases in activity were β-amino-butyric acid (BABA) (84.31 %), salicylic acid (55.97%), methyl jasmonate (282.99%) and ethephon (73.62%). The synergistic combination of methyl jasmonate and ethephon showed the highest statistically significant increase in enzyme activity (379.21%) when compared to the enzyme activity level of the blank treated control plant. In conclusion, as the foliar application of the synergistic combination of methyl jasmonate and ethephon has been shown to act as a potent inducer of the defensive protein peroxidase in kauri trees, it may be a potential treatment option for the kauri dieback disease. Further research is required to determine the effectiveness of the treatment option on the PTA infected kauri trees.