Policy and Technical Guide for

Prevention and Management of

Fusarium Wilt Disease of Banana (Fusarium oxysporum f. sp. cubense)

in ParticularTropical Race 4 (Foc TR4)

(Draft working paper)

Rome 2014

Table of Contents

Executive summary

Background

  • Background on banana Fusarium wilt
  • Brief history of the disease
  • Importance of the disease and current global status
  • The threat by TR4
  • Why it needs to be addressed

Biology and epidemiology of Foc

  • Biology of the pathogen
  • Race concept
  • Global distribution of Foc
  • Means of spread
  • Considerations needed for prevention

Develop and introduce policies for sustainable banana production and prevention of Foc TR4

  • Holistic and integrated approach for prevention
  • Ensuring multi sectorial / institutional consultation and coordination mechanisms
  • Enhancing awareness at all levels
  • Legislation and regulation for movement of planting materials
  • Strengthening seed production and certification system
  • Diversifying production system and varieties
  • Monitoring, risk analysis and reporting (using IPPC standards)
  • Inspection capacities at borders
  • Preparedness and contingency planning
  • Strengthening capacities for management

Technical procedures for surveillance and on farm management

  • Diagnosis and surveillance,
  • Implementation of sanitary and phytosanitary measures
  • Use of clean certified planting materials
  • Good agronomic practices
  • Eradication of initial infestation points
  • Disinfection of tools, vehicles and clothing
  • Training public officers and farm workers

Differentiated priority actions determined by risklevel

  • By countries already affected by Foc TR4
  • By countries at high risk
  • By countries potentially at risk

Differentiated priority actions according to production system

  • Production systems based on large-scale commercial Cavendish banana plantations
  • Production systems based on small-scale commercial Cavendish banana fields
  • Production systems based on mixed banana varieties
  • Production systems based on mixed cropping systems

Appendix 1: Six easy steps to protect farms against Foc TR4

Appendix 2: Differences between banana Fusarium wilt and other biotic constraints causing wilt-like symptoms.

Appendix 3: Activities that can be used to prevent and manage Foc TR4 in different risk areas and under different banana production systems.

EXECUTIVE SUMMARY

1. Fusarium wilt disease caused by Fusarium oxysporum f. sp. cubense (Foc) has been a major constraint to banana production for more than 100 years. The disease first gained prominence when it caused significant losses to Gros Michel bananas grown for export to the USA and Europe during the first half of the 20th century. To prevent the international export industry from complete collapse, Gros Michel was replaced with Cavendish bananas. However, in the last two decades Cavendish varieties recently succumbed to the disease, first in the subtropics and eventually also in the tropics. The reason for these outbreaks was the discovery of a new variant of the Fusarium wilt fungus, called Foc TR4, in Asia. Until recently Foc TR4 has been restricted to five Asian Cavendish-producing countries and Australia, but was recently discovered in the Middle East and Mozambique. This led to international concerns that the fungus is threatening bananas worldwide, and could severely endanger food security and also damage the international banana trade.

2. Banana Fusarium wilt is particularly difficult to control. The responsible fungus is soil-borne and can survive for decades in the absence of bananas, making it difficult to target with fungicides. Once susceptible bananas are planted in infested fields, the fungus infects it through the roots to cause a lethal wilt. Suckers taken from diseased areas spread the Fusarium wilt fungus over large distances, while it can be disseminated within and between fields with soil attached to shoes and plantation tools, vehicles and in irrigation water. The only means to protect bananas is to prevent the fungus from being introduced into disease-free fields through preventive measures, or by planting resistant varieties. Because of the wide host-range of Foc TR4, bananas grown asfood crop and for local markets, as well as that grown for international trade, are all potential targets. Proper awareness and appropriate legislation is thus needed to secure the future of bananas worldwide

3. The objective of this document is to provide technical guidelines to assist policy makers, regulators, scientists and producers to respond to the threat of Fusarium wilt, in particular to Foc TR4,for banana production in countries affected and those at risk. It is built around four components: policy development, guidelines for prevention and management of Foc TR4, priority actions according to risk and priority action according to production system.

BACKGROUND

4. Background on banana Fusarium wilt

Bananas are considered the eighth most important food crop in the world, and the fourth most important staple food in developing countries. The crop is grown throughout tropical Asia, Africa and Latin America, mostly to supply local markets. Smaller quantities of bananas are also produced in subtropical areas in China, Pakistan, the Mediterranean, Canary Islands, Australia, South Africa and Brazil. Approximately 13% of bananas produced worldwide enter the export market, and these consist primarily of Cavendish bananas. Cavendish bananas are also planted widely for local markets, and constitutemore than half of India’s 700 00 ha, and almost 90% of China’s 350000 ha of bananas. The remaining 60% of bananas grown globally consist of other sweet dessert varieties and cooking bananas. In Africa, cooking bananas and plantains comprise more than 70% of all bananas grown on the continent, whereas cooking varieties are found in smaller quantities in Asia and the Americas. Banana produces vegetatively, which makes them highly vulnerable to biotic and abiotic stresses.

5. Banana Fusarium wilt, or Panama disease as it is frequently called, is considered the most important disease of bananas in the world and one of the most significant diseases in modern agricultural history. The disease is caused by a soil-borne fungus (Fusarium oxysporum f. sp. Cubense) that survives in plantation soils as resilientchlamydospores. Once susceptible banana varieties are planted in infested fields, the fungus infects them through their roots and colonizes the vascular tissue in their rhizomes and pseudostems to cause a lethal wilt disease. When the disease spreads in-field or in banana-producing regions, significant damage can occur and production can be reduced by up to 100%. The soil-borne nature and ability of the fungus to survive for extended periods makes is extremely difficult to control. The only effective means to prevent significant losses are to prevent the fungus from being introduced into banana fields and by planting resistant varieties.

Brief history of the disease

6. Fusarium wilt of banana was first discovered in Australia in 1876, but gained prominence in Central America during the early 1900s. The causal organism, called Fusarium oxysporum f. sp. cubense (Foc), was most likely brought to the Caribbean much earlier with Silk bananas collected in Asia, but was only discovered when it caused damage to larger monoculture plantings of Gros Michel bananas in Panama and Costa Rica. Because of the disease’s early association with Panama and its unknown cause, it was named Panama disease, a name that is still used. From Central America the fungus was spread with diseased planting materials throughout the region, into South America and West Africa. The outbreak of Fusarium wilt caused significant damage to Gros Michel production in the areas where it was introduced. Eventually multinational banana companies were forced to replace their Gros Michel bananas with resistant Cavendish cultivars. Cooking bananas such as the East African Highland bananas and plantain also proved to be resistant. Consequently, Fusarium wilt was not more considered a major threat to bananas until the discovery of a new, highly virulent strain named Tropical Race 4 in Malaysia and Indonesia in 1990. The host range of this new strain is wider than that of the Central American strain, and its movement out of Asia raised concerns that the fungus can spread globally and once again threaten world banana production.

Importance of the disease and current global status

7. Banana Fusarium wilt has been described one of the most destructive plant diseases of the 20th century after it decimated commercial Gros Michel banana export plantations throughout Central America, with losses of prime agricultural land surpassing 100 000 acres. These losses disrupted not only the banana export industry, driving it to near bankruptcy and forcing it to continuously change production areas, but also severely disrupted social community structures, political systems and sensitive ecological environments in Latin America for decades. The ultimate replacement of Gros Michel with resistant Cavendish bananas brought temporary relief, as a new race of Foc is now severely affecting Cavendish bananas, mainly in Asia, but recently also in the Middle East and Africa. More concerning is that this new Foc race has the ability to threaten some of the banana varieties planted as staple food by subsistence farmers in Southeast Asia and Africa.

8. Banana Fusarium wilt of banana has been reported from all banana-producing countries except the South-Pacific islands, parts of Melanesia, countries around the Mediterranean Sea and Somalia.Strains of the pathogen are grouped based on their vegetative compatibility. Foc races 1 and 2 are widely distributed in Asia, Africa and the Americas. Foc subtropical race 4 occurs mainly in subtropical banana-producing countries such as Australia, South Africa, southern Brazil, Canary Islands and China. In Australasia, Foc TR4 can be found in most islands of Indonesia, in Malaysia and in Taiwan province of China, and is present in the Northern Territory of Australia, Mindanao in Philippines and in five banana-producing provinces in mainland China. It has, however, not been found in countries bordering affected ones, such as Thailand, Cambodia and Vietnam. In the Middle East Foc TR4 has been reported from Jordan and the Sultanate of Oman, and in Africa from Mozambique. Foc TR4 is more virulent than Foc subtropical race 4 and does not require predisposing factors to infect Cavendish bananas. With its wider host range and severity to Cavendish bananas, Foc TR4 poses a significant threat to globalbanana production.

The threat by TR4

9. Currently Foc TR4 is primarily a Cavendish monoculture problem. Once introduced into plantations, the fungus can cause significant damage. There are no examples where the disease has ever been eradicated or brought under control. In Malaysia and Indonesia Foc TR4 is now widely spread, and also affects varieties other than Cavendish bananas in small-scale farmer fields. Foc TR4 has destroyed almost 5000 ha of Cavendish and Latundan bananas grown by small growersin the Philippines, and in northern Australia commercial banana land was reduced by 80%. China has been most severely affected, with almost 40000 ha of farmer land now being infested with Foc TR4. The disease has spread rapidly in in infested areas in Jordan, Oman and Mozambique, and there are significant concerns that it could spread to small grower fields in the Africa. The threat of Foc TR4 to the two largest banana producers of bananas in the world, India and Brazil, is immense, as both countries produce significant amounts of Cavendish bananas. The large monoculture Cavendish plantations in Central America can also be severely affected by Foc TR4 ifthe fungus is introduced into the area.

Why it needs to be addressed

10. Foc TR4 was discovered more than two decades ago. It was limited to five Asian countries and northern Australia for a long time where it caused severe damage to Cavendish bananas and some local varieties grown by small-scale and subsistence farmers. The discovery of the fungus, for the first time in the Middle East and now in Africa, has raised concerns that Foc TR4 might decimate Cavendish bananas on a global scale and also affect bananas grown for local markets and consumption threatening the food security of smallholder farmers as well. It is notclear when and how Foc TR4 arrived in the Middle East and Africa norifit has been spread also to other countries already. Thus, considering the significant international movement of people and service providers working for the banana industry, the pathogen can severely affect the international banana trade which is worth US$ 9 billion, local banana production, food security and income generation of millions of people.

BIOLOGY AND EPIDEMIOLOGY OF Foc

Biology of the pathogen

11. The causal agent of Fusarium wilt of bananasbelongs to the section Elegans in the genus Fusarium. The fungus is characterized by micro- and macroconidia that are produced on branched and unbranched monophialides. Microconidia are one or two-celled, oval- to kidney-shaped and are produced in false heads. Macroconidia are four to eight-celled and sickle-shaped with foot-shaped basal cells. Chlamydospores are usually globose and are formed singly or in pairs in hyphae or conidia. They are resistant to desiccation and unfavourable environmental conditions, and enable the fungus to survive for more than 30 years in the soil even after their hosts have been removed. In the presence of banana root exudates, Foc chlamydospores, conidia and hyphae will germinate to penetrate susceptible plants.

12. Foc infects bananas by penetrating the root tips of the small lateral or feeder roots of the plant. Penetration takes place through wounds or injuries that expose the xylem vessels to the pathogen. The fungus then invades the water conducting tissue (xylem) where it produces microconidia that are carried up the plant, plugging the vascular tissue and reducing the movement of water. When blocked by sieve cells, the spores germinate and continue to spread until the entire water conducting system is blocked. Internal symptoms of Fusarium wilt of banana usually become visible as yellow, red or brownish dots and streaks localized in the vascular strands of the rhizome and pseudostem. In advanced stages of infection, rhizome discoloration is more prolific and the stains are more intense. Externally, infected plants show premature yellowing of the leaves which start on older leaves along the leaf margins and continue to the midrib until the leaves are completely brown and die. The yellowing progresses from the older to younger leaves, which distinguishes Fusarium wilt from bacterial wilt symptoms (which start with the youngest leaves). Eventually dead leaves will be hanging down the pseudostem. In some banana cultivars, leaves of Foc-infected plants will not turn brightly yellow, and green leaves will instead buckle and hang down the pseudostem. Splitting of the pseudostem just above the soil level may also occur. The heart leaf of affected plants eventually dies and the pseudostem will remain standing until it is removed or collapses.

Race concept

13. Based on pathogenicity to different banana cultivars, three

-races have been recognized in Foc. Foc race 1 causes disease in the Gros Michel (AAA) and Silk (AAB) cultivars. Foc races 2 attacks Bluggoe (ABB), and race 4 infects Cavendish (AAA) cultivars and most cultivars susceptible to Foc races 1 and 2. Foc race 3 has been omitted as a pathogen of banana, as it only attacks Heliconia spp. Strains affecting Cavendish bananas have been divided in subtropical (Foc STR4) and tropical (Foc TR4) strains, depending on the climatic conditions required to cause disease to Cavendish bananas. Substantial variation exists within Foc as measured by vegetative compatibility, volatile production, electrophoretic karyotyping and various molecular techniques. Twenty-four vegetative compatibility groups (VCGs) have been identified from a worldwide collection of Foc isolates.

Global distribution of Foc

14. The center of diversity of Foc is believed to be Southeast Asia, where most VCGs of the banana Fusarium wilt pathogen can be found. The first outbreak of the disease, however, was reported from Australia in 1876. Fusarium wilt became notorious when it destroyed banana plantations in Central America around the turn of the century. During the early 1900’s the disease was also recorded in Hawaii, South America, Asia and West Africa, and by 1950 it had spread to most of the banana-producing regions of the world. The disease was recently reported from New Guinea and Yap in the Federated States of Micronesia, which indicates that Foc spread has crossed Wallace’s line, originally demarcating the eastern border of the disease in the Indo-Malayan region. These outbreaks were mostly caused by Foc races 1 and 2. Foc STR4 was first reported from the Canary Islands, Australia, South Africa and Taiwan province of China. Foc TR4 was discovered in Malaysia and Indonesia in 1990, and thereafter reported from China (1996), Australia (1997) and the Philippines (2006). Another significant occurrence was the discovery of Foc TR4 outside Southeast Asia. It was also reported from Jordan in the Middle East and more recently from Mozambique in Africa.This raised significant concerns that the fungus affecting Cavendish can spread globally and result in immense damage to world banana production.