1[7] Colocasia bobone rhabdovirus [EDFS

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This leaflet is produced by the Ministry of Agriculture & Livestock, Solomon Islands, with support
from IPPSI: Improved Plant Protection in Solomon Islands, a project financed by ACIAR, the
Australian Centre for International Agricultural Research, Canberra. Authors: Helen Tsatsia, MAL &
Grahame Jackson, TerraCircle Inc.

Extension Fact Sheet 1:

Alomae & Bobone

Common name: Alomae and Bobone

Scientific name: Colocasia bobone rhabdovirus; Taro vein chlorosis virus; Taro badnvirus

Hosts: Colocasia bobone rhabdovirus and Taro vein chlorosis virus have only been recorded
from taro; Taro badnavirus has been recorded from kongkong taro and edu (vili, nepa), but
not in Solomon Islands.

Damage

Alomae (photo, left) is a deadly disease that has had a huge impact on taro production in
Solomon Islands. Most taros are susceptible. On Malaita, those taro are called ‘male’. The
impact has been worse on Malaita than on other islands. Previously, the disease was kept in
check by strict cultural practices. Nowadays, it is very difficult to grow ‘male’ taro in the
lowlands. In recent years, the disease has spread to other islands where it has been
devastating, such as the Weather Coasts of Guadalcanal and Makira. It is not unusual in these
places for entire gardens to be destroyed by Alomae.

Bobone (photos, centre & right) does not kill taro; it reduces the yield by about 25 per cent.
Plants usually start to produce healthy leaves after 4-6 weeks, and then appear normal. The
disease only occurs in a few varieties of taro. These
are called ‘female’ taro on Malaita. They are
resistant to Alomae.

Biology and Life Cycle

Insects (photo, right) spread the viruses that cause
Alomae and Bobone:
• The rhabdovirus is spread by Tarophagus, a

planthopper

• The badnavirus is spread by Planococcus and

Pseudococcus; these are mealybugs.

The planthoppers and mealy bugs suck up the viruses as they feed; the viruses multiply in the
insects, which then spread them as they move and feed on healthy plants.

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When ‘male’ plants are infected by the rhabdovirus, the plants develop Alomae, and die.
When ‘female’ plants are infected by the rhabdovirus, they develop Bobone, but they recover.

Apart from being spread by insects, the viruses are also spread in planting material. It is likely
that all taro are infected with Taro badnavirus, without showing symptoms, or only rarely do
they show symptoms. The viruses spread from mother plants to suckers. Also, it is likely that
all ‘female’ taro are infected with the rhabdovirus. Bobone often occurs after planting, when
plant hoppers are absent. Possibility, stress at planting causes the virus to multiply.

Alomae is spread from one garden to another in diseased ‘tops’ and suckers used for planting.

Signs and Symptoms

It is important to inspect taro gardens regularly. Look at the youngest leaves. If the plant has
Alomae, the leaf will be:
• Stunted, slightly curled, with tip bent backwards, crinkled, and often paler than older

leaves.

If the plant has Bobone, the leaf will be:
• Stunted, thickened, curled or partly curled, darker green than usual, and the leaf stalks

will have galls – small outgrowths.

Plants with Alomae stop growing and the youngest leaf remains rolled and yellow. Plants
with Bobone produce leaves that are stunted and distorted, and then healthy leaves develop.

Management

Cultural control:

Alomae is best controlled by cultural methods. These methods rely on farmers’ understanding
how the disease spreads. It is very important that farmers:
•  Understand that insects spread Alomae, as they fly between plants and gardens;
•  Work together, each one applying the methods in his or her garden;
•  A village group is formed, which meets regularly, exchanges ideas, and the members help

each other;

• Plant resistant varieties: ‘Female’ taros are resistant to Alomae, and they can be used

where the disease is severe, especially in the lowlands.

Farmers should do the following:

•

Make new gardens as far away from old ones as possible;

• Avoid taking planting material from diseased to new gardens;
• Pull out Alomae plants carefully, making sure that any planthoppers are trapped in the

leaves or between the stalks – or put a rice bag over the plants before pulling them out;
and then burn them;

• DO NOT pull out plants and leave them in the garden or throw them into the bush – the

insects will come back again.

Biological control:

Cyrtorhinus, a bug that feeds on the eggs of Tarophagus, reduces the population of the plant
hopper, but experience shows that it is not enough to stop the spread of Alomae.

Chemical control:

Regular spraying with pyrethroid insecticides (permethrin or lambda cyhalothrin) will kill
Tarophagus and reduce Alomae. It will not prevent Bobone.