Mystery sago palm disease

Editorial, Normal

The National, Tuesday 14th May 2013


SAGO is an important staple food in many lowlands and coastal areas of Papua New Guinea. In Bougainville, unlike in other provinces, sago is not usually harvested for its starch, but for its leaves which are an excellent source of house thatch.  

Roofs made from sago leaves are more durable than those made of other materials, lasting 5-10 years on average before it is replaced.  The midrib of the sago leaflet can be crafted into an arrow as strong as steel, for hunting birds and other wild animals. 

The image of the lush green Bougainville rainforest with its broad leaf sago is instilled in the peoples’ hearts. 

This landscape is now changing.  In 1990, around the time of the crisis, some sago trees were showing dead leaves, making them unusable for roofing, and then the trees began collapsing.  This decline was first observed around the former administrative centre of Arawa in central Bougainville, and then in other parts of the island as the disease spread.  Arawa-based tour operator Zhon Bosco Miriona raised the alert with Catherine Sparkes, a representative from the Christensen Fund.

The Christensen Fund is a non-governmental organisation working on the island to preserve the culture and biodiversity of Melanesian countries.  

Responding to the request for technical assistance from Miriona and the Christensen Fund, the National Agricultural Research Institute (Nari) conducted a survey on the decline last month. National Agriculture Quarantine and Inspection Authority (Naqia)  officers were also part of the survey team.  

The survey covered areas of the west and east coasts of Buka Island and the northern regions of Bougainville Island, where the decline appeared to be moderate but spreading.

Symptoms of the decline appears first as yellowing or browning of older leaves and occurs in sago of any age.  

At the bottom of the stem near the soil line, resin-like fluid can be seen oozing out, as well as small holes made by invasion of insects.  When such sago trees are cut down near the soil line, a circular brown rot in the pith is evident, giving the tentative name of the disease, sago pith rot.  

At an early stage of the decline, the rot is restricted to the pith around the base of the tree and does not appear to extend to the top or to the roots.  However, as the disease advances, the rot can reach the cortex and will eventually lead to the collapse of an entire palm.  

A number of locals reported that the decline is more severe for upland sago than the sago stands in swamps, which was also evident during the survey. 

Several different species, sub-species, and varieties of sago palm are recognised in the country, and it is noted that the majority of sago in the PNG mainland is classified as Metroxylon sagu, by far the most important economic species, while most Bougainville sago palms belong to another species, Metroxylon salomonense.

They have different modes of reproduction.  

M. sagu reproduces by suckers, while M. salomonense propagates by seed.  Therefore, Bougainville sago may have a high level of genetic variability that may be useful in identifying tolerance to the decline.

Despite the seriousness of the problem, the decline has not attracted much attention and reports coming from locals are important for the accurate documentation of the problem.  

While Bougainvilleans do not cut down sago palms for starch processing, this is changing in some areas now where sago is becoming important as a source of building material and food.  This is making difficult the monitoring of the rot progressing inside the tree.  However, an observation for insect damage, resin-like ooze, and an onset of leaf discolouration can signal the problem.  

Residents in Bougainville or other sago growing areas are encouraged to report such observations to Naqia or Nari.  

There are similar reports from other provinces, including Western Province.  At this stage, we are unable to establish whether these problems are similar to the situation on Bougainville.

With intermarriage to people from the Sepik and Gulf Provinces who use sago starch more often, a few families in Bougainville are starting to harvest sago for its starch, but the practice is still not very common.  However, in the era of climate change, sago can be an excellent famine food in times of crop failure.  

As such, the goal of this survey is to determine the cause of the sago trees decline and recommend solutions to mitigate the impact of the decline on the socioeconomic environment in Bougainville. 

The rot affecting sago on Bougainville may also be present in other provinces, where sago starch is a staple food.  

The survey and its findings will also be of benefit to other sago growing areas.  

The knowledge of the decline and the solutions to the problem will be shared with all stakeholders for improved food security.

The team will re-visit the island in July to investigate the status of sago stands in central Bougainville.