Kauri dieback, caused by the fungus-like pathogen Phytophthora agathidicida, is causing widespread deaths of kauri trees throughout northern New Zealand. It seriously threatens the survival of these trees and the ecosystem they dominate.
Kauri dieback, which is incurable and fatal, was first discovered on Great Barrier Island in the 1970’s and through the transfer of infected soil (mainly by humans) the disease is now widespread in Northland.
It is likely that Kauri dieback has existed in New Zealand for centuries, possibly predating human arrival, but only more recently has it become a danger to Kauri.
The Department of Conservation has introduced boot washing stations at track entrances to Kauri forests throughout Northland, but a recent study concluded that 83% of track users fail to decontaminate their boots. A further study has found that 71% of all infected trees are within 50 metres of a public walking track.
Armed with this evidence, the Auckland City Council has closed all public access to the Waitakere Ranges after the rate of infection has doubled in the last five years, but at this stage Northland forests are open to the public.
Of particular concern is the great Tāne Mahuta and surrounding giant Kauri trees in the Waipoua Forest near Dargaville. Tāne Mahuta is somewhere between 1,250 and 2,500 years old and the remnant of an ancient subtropical rainforest.
Plant and Food Research are part of a wider group of scientists from many organisations studying the disease and trying to find ways of reducing the spread and impact of this disease. Dr Ian Horner is leading the Plant & Food Kauri dieback team and he approached Luisetti Seeds to supply New Zealand blue lupin seed for soil baiting. Luisetti Seeds were delighted to be able to donate this seed (grown in Rangiora) to such an important national cause.
A major part of the work carried out by the Plant & Food team is testing soil samples collected throughout kauri lands to determine where the pathogen is present and this is where the lupins come in. Soil “baiting” is a technique that has been used for decades to trap Phytophthora in soil samples, and the New Zealand blue lupin has proven to be a particularly useful bait for trapping the kauri dieback species. The baiting technique relies on the fact that Phytophthora has a motile zoospore stage. These zoospores are tiny, only about 5 um long, and have two flagella (tails) that help them swim through the soil water to attack plant roots. To catch them soil samples collected from forests are flooded, and freshly germinated lupin seeds are floated on the surface. The zoospores swim through the water and colonise the lupin root (the bait), where it can be retrieved easily and grown on agar plates for microscopic identification.
By doing hundreds of such samples scientists are gradually filling in the map and identifying where the pathogen is present, or absent, in our kauri forests. This helps forest managers to stop the disease spreading to other areas, or to identify areas that need to be protected to prevent the disease entering.
So, in a small, but important way, the New Zealand blue lupin from Luisetti Seeds is helping in the battle to save our kauri forests.
Original parent Viceroy (showing yellow leaves characteristic of BYDV infection). A trial using a resistance wheat gene to control Barley...