On the right: TR4 affected plants in The Philippines
The Australian banana industry will need a diverse strategy to successfully fight Panama Tropical Race 4 (TR4) and maintain production in the event of TR4 becoming more widespread. These were the findings of a three-person Australian banana industry team who undertook a 12-day study tour of banana production areas in the Philippines and Taiwan. ABGC Research and Development Manager, Rosie Godwin, reports.
With team members, Tony Pattinson, principal Nematologist, from the Queensland Department of Agriculture and Fishers (DAF) and Tully banana grower Patrick Leahy, I was part of a 12 day tour of the Philippine and Taiwan study tour.
Our visit was part of industry planning for future production strategies following the confirmation of Fusarium oxysporum f. sp. cubense Tropical Race 4 (TR4) in the Tully Valley.
TR4 can persist for decades in soils, cannot be eradicated and is easily spread though the movement of infested soil, water and planting material.
In countries such as the Philippines and Taiwan, major contributors to the rapid spread of TR4 across production areas were flood waters from contaminated areas, irrigation water from infested dams and rivers, the use of infested planting material and lack of on-farm biosecurity measures.
While TR4 is currently contained to a single property in north Queensland, exclusion is the best way to contain the disease and prevent its spread to other farms.
This can be achieved through effective quarantine and biosecurity measures, awareness and training.
However, what is available to farmers to help maintain production if their farms are unlucky enough to become infested with TR4?
Although the Philippines and Taiwan are two of the world’s banana regions most affected by this disease, the study tour found both countries are still managing to produce bananas, by
employing a range of measures best suited to their local conditions.
They also found stacking a range of control measures can have considerable benefits to production.
This includes the use of
• TR4 tolerant varieties
• Using clean planting material
• Minimising the build-up of the fungus in the soil by: employing crop and soil management strategies; detecting infected plants early and destroying them efficiently
• Crop destruction and fallowing
Tolerant Varieties
Most important was the use of tolerant varieties such as the Giant Cavendish Tissue Culture Variants (GTCTV 218 and 219) which are being more widely adopted in Asia.
These were selected and developed by Taiwan Banana Research Institute (TBRI) and Bioversity International for their ability to grow in soils heavily infested with TR4.
In commercial trials, these varieties appear to remain productive even after four ratoons, while Grande Naine was severely affected even in the primary crop.
GCTCV 218 (Formosana) is moderately resistant to TR4 and more acceptable by growers because its big bunches and good fruit quality mean that it can be packed, ripened and marketed together with conventional Cavendish varieties.
The disadvantage of GCTCV 218 is that it is tall, has a high number of off types and takes two to three weeks longer to mature than Grande Naine.
GCTCV 219 is a Philippine selection of GCTCV119 from Taiwan and is being used in the Philippines for TR4 management.
It is more resistant to TR4 and has sweeter fruits than GCTCV 218; however its productivity and fruit quality are not as good.
GCTCV 219 is taller, more of a floater, and longer maturing.
It also has fewer hands and straighter fingers, and yields are more likely to decline over time.
In the Philippines and Taiwan, recurrent selection has been the approach used to improve both disease resistance and agronomic characters of tissue culture clones.
Other promising varieties developed by the TBRI are Tai-Chiao No.5 and Tai-Chiao No.7.
TBRI now recognizes TR4 is likely to spread to other banana producing countries and have started a program of developing new varieties for the global Cavendish market.
In Australia these varieties, and others showing tolerance to TR4, are being evaluated in both experimental trials as well as on some local farms.
The study tour participants suggested farmers could play a key role in identifying and selecting individual plants with the best agronomic traits for inclusion in plant improvement programs or improving material on their own farms.
Crop and soil management practices
Crop and soil management are also important measures which are being tested in the Philippines and Taiwan.
The aim is to create an environment favouring the performance of tolerant varieties and reducing the build up of the pest fungus in soils.
This includes encouraging microbial diversity in soils to provide competition to TR4, minimizing erosion to prevent the loss of soil fertility and soil structure, and decreasing competition from weeds.
This can be achieved by modifying land preparation practices to minimize soil disturbance and improve drainage.
Beneficial ground covers such as pinto peanut are also being tested in the Philippines to reduce erosion, improve soil structure, and decrease the presence of weeds.
Pinto peanut is well suited to high rainfall areas of the tropics and subtropics such as north Queensland.
It is a low growing perennial legume that is drought and shade tolerant and adds nitrogen to the soil.
It grows to form a thick mat which protects the soil surface and out-competes weeds which may act as alternative hosts to TR4.
In Taiwan, research has also been conducted with organic systems using the more resistant cultivars and found bananas could be produced in a continual ratoon system for up to eight
years with less than 10% losses from the disease.
Surveillance
Surveillance, early detection and rapid destruction of infected plants are other important strategies employed by large companies in the Philippines to slow the spread of TR4 and minimise the build up of inoculum in soils.
Large companies have greater financial and technical capability than small holders.
The extent of TR4 infestation is not known in the Philippines and is likely to be still increasing.
Currently thousands of hectares have been affected. In a recent survey in of 500 small holder growers in the Davao del Norte region (~45,000 ha), at least 90 per cent growers had the disease, 40 per cent with more than 20 per cent of their plants affected and 40 per cent were seeing TR4 for the first time.
More than 3000 ha are estimated to have been abandoned.
Originally infested plants were destroyed by burning with rice hulls; however this has been found to be ineffective at killing both the fungus and the infested plant.
Other destruction methods, including the cutting down and treatment of plant material with urea and lime, are currently being trialled and initial results have found it to be more effective and less expensive than burning with rice hulls.
Clean material
The use of clean planting material produced from tissue culture is another fundamental strategy used in the Philippines and Taiwan to exclude TR4 from new production areas, minimise spread within farms, provide better plant establishment and better growth in infested soils.
In Taiwan, at least six million tissue culture plants are used each year.
Previously, the movement and use of infected bits and suckers has been a significant contributor to TR4 epidemics in these and other countries.
Tissue culture is the only way to guarantee planting material is disease-free and in Australia we are fortunate to have a quality assurance scheme such as the Quality Banana Approved Nursery (QBAN) that certifies tissue cultured plantlets as disease-free.
Tissue culture plants are also guaranteed free of other diseases including nematodes, which may make weaken plants and make them more susceptible to TR4.
Fallowing and rotational cropping
Fallowing and rotational cropping are strategies used widely in Taiwan for inoculum management in conjunction with the use of tolerant varieties.
This is because the high inoculum levels in the soil and challenging environmental conditions puts tolerant varieties under a strong disease pressure. Approximately one third of the production area is annually cropped because of TR4 and to avoid the typhoon season.
In some areas, fallowing and rotations with submerged crops such as paddy rice and to a lesser extent taro have significantly decreased the incidence of TR4 compared to areas where bananas are still grown as a monoculture.
Observations from the study tour indicate there currently is no single management solution to TR4 in commercial banana production in countries like the Philippines and Taiwan.
Quarantine, on-farm biosecurity and early detection are crucial to preventing and slowing the spread of the disease.
Clean planting material and TR4 tolerant cultivars like those from Taiwan, facilitate banana production in a continuous ratooning system, but they have agronomic disadvantages compared standard Cavendish varieties like Williams.
Environment and management conditions can significantly influence the way a cultivar performs and the speed with which inoculum levels build up.
If the disease were to become widespread in north Queensland, a system of integrating as many management strategies as possible is the best way to keep banana farms productive.