Hope for island’s sago palms

 By TOSHIRO SHIGAKI

“SAGO palms covered the whole sky. When it rained, not a single drop fell on me”.

When a team of scientists from the National Agricultural Research Institute (NARI) and National Agriculture Quarantine and Inspection Authority (NAQIA) visited a village in the vicinity of Buin, southern Bougainville, a local resident told us how dense the sago stands used to be.  

All we could see though, was a sparse sago population growing among other more dominant tree species.

A mysterious sago decline started in the early 1990’s, just after the “crisis”, in the Arawa area in Central Bougainville.

It spread to almost all districts of Bougainville. It is now penetrating Buka Island north of Bougainville Island.  

The sick trees are almost always associated with an endemic species of weevil that appears to attack the trees at the bottom of the trunk.  

Inside the trunk, a globular brown rot damages the pith.  The rot appears to be fungal in nature, perhaps vectored by weevils.  

Older fronds often turn yellow, and the trees collapse as the rot reaches the cortex.

Sago palm has cultural importance in Bougainville.  

Its broad leaves are used as a durable thatching material.

These leaves were freely collected  when sago trees were commonplace.  

These days,  people are willing to pay as much as K50 for a sago tree that is still surviving with healthy leaves.  

Others have to resort to tin sheet and other material for their roofing needs.

In Arawa, no tree survives to the flowering stage.  

But in the Buin area, it is common for the graceful sago trees to flower and bear seeds.   

These surviving sago trees may give us hope for restoring the once legendary sago forests on the island.

The sago palms found in Bougainville are distinct from the species that commonly occur in other parts of PNG.  

While the mainland sago reproduces by suckers, Bougainville sago propagates by seeds.

This implies a broader genetic diversity among Bougainville sago trees than those on the mainland.  

It is likely that the sago trees surviving in Buin and other areas are tolerant to the decline.  

If that is true, it is possible to use the seeds from these sago palms for reforestation.  

TISSUE CULTURE

This will require a careful assessment of the level of tolerance among the surviving population.

Sago seeds are, however, difficult to collect because of the height of the fruits at the apex of the tree, which can reach as high as 20 metres.   

Sago seeds also  remain viable for a short time after maturity and do not tolerate long term storage. 

Therefore, tissue culture may be a more realistic method to propagate tolerant lines.  

The protocol for in-vitro culture of Bougainville sago must be developed for efficient propagation of planting materials.  

It should be one of the best way to mass propagate the plant and also a safe way to preserve genetic materials against pest and disease assaults and climate change.

Other control measures include the use of pesticides and fungicides but they are both costly and detrimental to the environment.  

An alternative is a biological control using fungi that kill weevils.  

Considering its importance in culture and for food security, any attempt to implement controls must be discussed with all stakeholders.

Sago trees that are susceptible to the decline must be also protected to preserve genetic resources. The germplasm will be invaluable for future breeding programmes.  

But where can we find such sago trees when the problem appears to have spread to almost all areas in Bougainville?  

The answer is that isolated islands may be protected from pests and diseases by virtue of their isolation.  

The NARI/NAQIA team visited Zune Island about 5km off the Central Bougainville coast.  

There, sago trees were healthy with no evidence of the decline affecting the mainland village just across the narrow straight.  

It is urgently needed to quarantine the island by prohibiting the traffic of sago materials.

The NARI/NAQIA team has completed two one-week surveys that covered the entire province, in April and August this year.  

A workshop will be held in Arawa later this year to report the survey and laboratory results to all stakeholders in Bougainville.  

Control measure will be discussed during the workshop based on the survey and lab findings to re-establish the lost sago stands in Bougainville.

This project is supported by a grant from The Christensen Fund, aimed at preserving biological diversity of sago and associated cultural heritage of Bougainville. – NARI