In the first half of the twentieth century,
the banana in shops around the world was a variety called Gros Michel. A soil fungus destroyed so many plantations in Central America that by the nineteen sixties the export industry had switched to Cavendish, which resisted that strain.
The disease was named Panama disease, or Fusarium wilt of banana.
Today a new strain, Tropical Race Four, kills Cavendish too,
and it has spread from Southeast Asia to Australia, the Middle East, Africa, and since twenty nineteen, Latin America.
There is no cure, and no fungicide that controls it in the field. The fungus survives in soil for decades.
So the whole battle is about keeping it out, finding it early, and containing it. In this video: how the disease works, how to recognise it, how it spreads, farm biosecurity, what to do if you suspect it, and the varieties that offer some hope. In many countries Tropical Race Four is a notifiable disease, so follow your national rules.
Panama disease is caused by the soil fungus Fusarium oxysporum
forma specialis cubense. Some scientists now classify Tropical Race Four as a separate species,
but the disease is the same. Its strains are grouped into races by the varieties they attack.
Race one destroyed Gros Michel and still attacks many local varieties,
Tropical Race Four attacks Cavendish and a wide range of other bananas,
and other strains attack other groups.
The fungus enters through the roots, grows into the water-conducting vessels, and blocks them. The plant wilts and dies, while the fungus forms thick-walled resting spores, called chlamydospores, that return to the soil and can survive there for more than thirty years, even without bananas.
The first outside signs are on the older leaves. They turn yellow, usually starting at the edges, and the yellowing moves to younger leaves.
Then the leaves collapse at the stalk and hang down around the pseudostem like a skirt, while the youngest leaves may stay upright for a while.
The base of the pseudostem may split.
The decisive sign is inside. Cut across the pseudostem near the base. In an infected plant, you see yellow, reddish-brown or dark brown to purple strands, the blocked vessels, in the outer leaf sheaths,
and the discolouration runs up and down the stem and into the corm. The fruit itself usually looks normal.
Two other diseases look similar from outside:
Moko and blood disease, caused by bacteria,
and banana Xanthomonas wilt. These usually rot the fruit inside and ooze bacterial slime from cut tissue.
Only a laboratory test can tell Tropical Race Four from other strains, so if you suspect it, do not move anything from the plant and contact your plant protection authority.
The fungus moves wherever infested soil and infected plants move. The most important ways are infected suckers and corms used as planting material, soil stuck to boots, tools, vehicles and machinery, and water: run-off, drainage and floods from infested fields.
Animals and people walking between farms carry it too. A single truck tyre of infested mud can start a new outbreak on a farm many kilometres away.
Because there is no cure, biosecurity is the main defence, and it works.
Use only clean planting material: tissue-culture plantlets from certified sources, never suckers from other farms.
Fence the farm and have one entry point. Keep visitors' vehicles outside, and give people clean boots or boot covers. At the entry, set up a footbath or boot-wash station with a disinfectant recommended locally, such as a quaternary ammonium product,
and brush the soil off before dipping, because soil protects the spores.
Wash down vehicles and machinery that must come in, and clean tools before moving between blocks.
Manage water so that run-off from roads or neighbouring farms does not flow into your plantation.
Keep soil healthy, with good drainage, organic matter and ground cover;
healthy soils can slow the disease, although they cannot stop it. And check your plants every week, looking for yellowing older leaves and collapsing petioles.
If you find a plant that might be infected, act calmly and quickly.
Do not cut it open further, do not move soil, suckers or leaves from the spot, and keep people and animals away.
Mark the area and report it to your plant protection authority, which can take samples for a laboratory test.
If Tropical Race Four is confirmed, the usual approach is containment.
The infected plant and its neighbours are killed and left in place, often covered, the area is fenced off, and no soil or plant material leaves it.
Equipment used there stays there. The rest of the farm continues under strict biosecurity. Many farms in affected regions have kept producing for years by containing small outbreaks early.
No commercial Cavendish is fully resistant to Tropical Race Four, but there is progress.
Somaclonal selections of Cavendish from Taiwan, such as Formosana, show useful tolerance and are grown where the disease is present.
Some other banana groups are resistant, although they may not suit the export market. A gene-modified Cavendish line with resistance has been approved for growing in Australia, and breeding programmes around the world are working on new resistant varieties.
Planting a more tolerant variety in infested soil buys time, but it does not replace biosecurity.
Tolerant plants can still carry and spread the fungus.
To recap.
Panama disease is a soil-borne Fusarium wilt with no cure,
and its spores survive in soil for decades.
Tropical Race Four attacks Cavendish.
Look for older leaves yellowing from the edges,
leaves collapsing into a skirt, and, decisively,
reddish-brown to purple strands inside the pseudostem. It spreads with planting material, soil and water.
Use clean tissue-culture plants, one farm entry, boot and vehicle hygiene and water control. If you suspect it, isolate the spot and report it. And use tolerant varieties where available, together with biosecurity.
For more on bananas and every other crop, visit laisha.ai. Thank you for watching.
