Mango malformation disease

Symptoms

The most common symptom is abnormal, compact development of flowers and shoots. Mango trees can have both normal growth and growth affected by mango malformation disease at the same time.

Flowers

• Flowers are the most prominent plant part affected.
• The flower stems or panicles become shortened, thickened and highly branched, producing up to 3 times the normal number of flowers. Panicles can have high numbers of male flowers compared with perfect flowers.
• The flowers themselves can be enlarged, sterile and not bear fruit.
• Panicles may also form dwarfed and distorted leaves instead of flowers.

Shoots

• The growing points (buds) produce misshapen shoots with short internodes and brittle leaves.
• The leaves are much smaller than those of healthy plants and re-curve towards the stem giving a squat, bunchy-top appearance.

Plant stage and plant parts affected

• Mango malformation disease can affect mango trees of all ages.
• Mature plants with the disease can have abnormal growth of leaves, shoots and flowers.
• Nursery plants (seedlings and young trees) can be severely affected with malformed leaf growth causing stunting.

May be confused with

Excessive use of some plant growth regulator chemicals that reduce tree size and increase fruit yield, can also cause a shortening of internodes on the vegetative shoots, causing a tight, spiralled pattern like a rosette. Flower panicles can also have more flowers.

Herbicide damage or other environmental stresses can produce deformed leaves and shoots, or erratic/unusual growth that may also be confused with mango malformation disease.

If you are unsure or suspect mango malformation disease, report it.

Mango malformation disease is found in many mango production areas internationally including Africa (Egypt, South Africa, Sudan and Swaziland), Asia (Burma China, India, Israel, Malaysia, Oman, Pakistan and Sri Lanka), Spain and the Americas (Brazil, El Salvador, Mexico, Nicaragua, USA (Florida) and Venezuela).

Fusarium mangiferae was first detected in Australia in 2007. It is known to occur in the Northern Territory and has been successfully eradicated from an isolated incident in Queensland in 2009.

Fusarium mexicanum has not been detected in Australia.

Fusarium sterihyphosum has been detected in Australia on a host other than mango and not in association with mango malformation disease.

Mango plants (Mangifera indica).

• Fungal spores (conidia) are formed on live and dead infected plant parts such as malformed flower panicles.
• Malformed flower panicles increase fungal spore production as they age.
• The mechanism for disease transmission within a tree or between trees is poorly understood.
• Infection occurs in emerging flower and shoot buds.
• The fungal spores germinate and colonise the host tissue in the flower or stem bud and do not appear to move any further into the rest of the plant.
• The disease spreads slowly between plants within affected orchards.
• The disease can remain dormant for several years before showing symptoms.
• The disease is not spread within fruit or seeds.

Mangoes are an important crop in Queensland. The Australian mango industry produces about 52,000 tonnes of fruit annually, providing a gross value of production at the farm gate of approximately $167 million per year, of which 43% are grown in Queensland (source: Australian Mangoes 2021/2022 Annual Report).

Mango malformation disease does not kill trees, but it can severely reduce fruit yield as the malformed flowers do not set fruit.

Internationally, mango malformation disease is regarded as an economically important disease of mango. Estimated crop losses have been reported to be as high as 80–100% in some regions of the world.

Home gardeners can also be impacted by mango malformation disease as affected mango trees are unlikely to bear fruit or will have reduced fruit yield.

There are no impacts on human health from mango malformation disease and mango fruit produced by affected trees is safe to eat.

Mango malformation disease can be spread by grafting with infected budwood. The movement of infected plant material such as budwood or plants could spread the disease long distances. Movement restrictions are in place in Queensland to prevent the introduction of mango malformation disease.

Within an orchard, the disease spreads slowly. The fungal spores (conidia) can be spread within and between trees on air currents, in dew droplets or rain splash, or on falling infected plant debris.

Reports of severe infection in nursery plants overseas may be associated with growing seedlings and young trees under the canopies of infected mango trees.

Inspect mango trees during the flowering season for stunted, thickened, highly-branched flower panicles that are producing flowers that are larger than normal or abnormally high in number. Also examine flower panicles for dwarfed and distorted leaves growing within the panicle instead of flowers.

Check for malformed leaves and shoots throughout the year. Affected stems will have small leaves that curve back towards the stem and have a squat, bunchy top appearance.

If you see symptoms, contact Biosecurity Queensland on 13 25 23, for advice. Do not move any plant material off your property as this can spread the disease.

• Protect your farm from emergency plant pests
• Understand good farm biosecurity
• Visit the farm biosecurity website

Mango malformation disease is prohibited matter under the Biosecurity Act 2014. This means that by law it must be reported immediately to Biosecurity Queensland on 13 25 23 or the Exotic Plant Pest Hotline on 1800 084 881.

If you think you have found mango malformation disease, you must take all reasonable and practical steps under your control to minimise any associated risks. This is called a general biosecurity obligation (GBO).

Movement restrictions are in place to protect Queensland from mango malformation disease. A biosecurity certificate is required to move a mango plant material (excluding destemmed fruit) into Queensland unless sourced from a state or part of a state that is certified free from mango malformation disease.