Australia's varied climate offers excellent growing conditions for a range of plants and trees, but this environment also harbours a lot of pests and diseases. A significant proportion of Australia's economy depends on agriculture, so it's unsurprising that the government is vigilant to the risks that some of these pests and diseases present. Panama disease is a dangerous type of fungus that threatens Australia's thriving banana plantations. Learn more about the disease, how it affects crops, and how everybody in Australia needs to stay vigilant to the signs of this condition.
About bananas
Many people believe that bananas grow on trees because of the size of the stems. In fact, the banana is the largest herbaceous flowering plant in the world, with pseudo stems that can reach nearly 8 metres in height. Each of these stems normally produces a bunch of bananas. A fully-grown banana plant in your garden will certainly have the same impact as many species of tree.
The banana is one of the oldest known cultivated plants in the world. All cultivated banana plants around the world (including Australia) descend from just two wild species. Wild bananas have pea-sized seeds, but the edible variety grows without seeds due to a process called parthenocarpy. As part of this process, the fruit develops without fertilising the ovule, which means plantation farmers must produce new plants through tissue culture.
This process efficiently allows farmers to grow billions of bananas every year, but there is one important drawback. Almost all commercial banana plants are genetically identical clones. As such, commercial banana plants are highly vulnerable to disease. A single outbreak of disease can wipe out an entire plantation, and it isn't yet possible to replace the current commercial variety with any other type of banana.
About Panama disease
Panama disease originates from a soil-borne fungus called Fusarium osysporum. Plants are susceptible to four races of the Panama fungus, as follows:
- Race 1 infects Lady Finger, Sugar and Ducasse banana plants but not Cavendish (the main commercial plant)
- Race 2 generally only infects cooking bananas (including Blue Java)
- Race 3 does not infect bananas and will only attack other plants
- Race 4 infects most banana varieties, including Cavendish, and poses the greatest threat to Australia.
Race 4 further divides into two strains. Subtropical Race 4 produces symptoms in Cavendish bananas. In Australia, this strain is under quarantine in parts of Queensland, New South Wales and Western Australia. Tropical race 4 has, so far, only appeared in the Darwin area, where the fungus remains under strict quarantine control. In parts of South East Asia, tropical race 4 has had a devastating effect on banana plantations.
Signs and symptoms of Panama disease
Plants with Panama disease will normally start to yellow and their leaf edges will die. Over time, the leaves can turn brown and dry out, eventually leaving a plain stump, with a skirt of dead leaves. The stem may split, and water-conducting tissue will often start to discolour when the fungus infects plant tissues. An infected plant will rarely produce fruit.
It's easy to spread the fungus via infected material. For example, if you cut off infected stems or leaves, the fungus can then spread to other plants that come into contact with this debris. The disease can also spread naturally via root to root contact and through the soil. What's more, if you move infected soil, you can spread the disease further. The fungus will even transfer to other plants on any equipment you use around infected banana plants.
Some growers mistake the symptoms of Panama disease for nutritional problems or water stress, but these conditions do not normally cause discolouration of the plant's internal vascular tissues. The symptoms may also look like the side effects of Moko or blood disease, but these problems do not yet occur in Australia.
Dealing with Panama disease
It's not possible to cure Panama disease. If growers believe their plants are infected, they should contact the state plant health inspector and ask that he or she takes a sample. If an inspector confirms an outbreak in a plantation, he or she will issue an Inspector's Approval, which outlines strict hygiene measures that everyone must meet to stop the infection spreading.
Once you detect the fungus, it's vital that you destroy all infected plants. It's also important not to disturb an infected area more than necessary, or you may spread the pest via soil or plant material movement. Kill the plants with glyphosate injection but do not chop the plants down. The authorities recommend that you fence off infected areas.
Prevention of the disease is vital for farmers and homeowners alike. Only buy plant cultures from a certified disease-free supplier. Stay vigilant to the symptoms of the disease, regularly inspecting the leaves for any early signs of infection. Banana farmers should also avoid sharing machinery with other growers, as the disease commonly spreads when infected soil and material is left on farm equipment.
Panama disease is a dangerous fungal pest that threatens banana plantations across Australia. Farmers and homeowners alike should take steps to make sure the disease does not affect their plants. For more information, contact a company like Australian Tree Consultants Pty. Ltd.
