DR. D.Y. PATIL BIOTECHNOLOGY AND BIOINFORMATICS INSTITUTE
Banana (Musa spp.) is one of the most consumed fruit across the world and the most significant fruit in terms of production volume and market. Bananas are grown in over 135 countries and are a staple crop for nearly 400 million people as well as an important source of revenue in many developing economies. But, the banana is now on the edge of extinction as Fusarium wilt, often known as the Panama Disease, poses a great threat to its existence.
The disease was discovered in Australia and has since spread globally. For more than 20 years, it was confined to east and parts of Southeast Asia, but since 2010, the disease has spread to five additional Asian countries (Vietnam, Laos, Myanmar, India, and Pakistan), across the continent in the Middle East (Oman, Jordan, Lebanon, and Israel), Africa (Mozambique), as well as Colombia, marking the strain’s first occurrence in the Americas.
A similar situation occurred in the 1950s when the crop was ravaged by Panama Disease caused by the spread of a toxic, soil-inhabiting fungus. Banana producers throughout the world were desperate for a solution and turned to the Cavendish. The Cavendish was disease resistant and met other commercial requirements, including the ability to remain green for several weeks after harvest (excellent for shipping), a maximum output rate, and a pleasing appearance in stores. Furthermore, global fruit producers did not have any disease-resistant variety available that could be ready for global exporting quickly.
THE PANAMA DISEASE
The Panama Disease is referred to as the Fusarium wilt of banana. It is caused by the fungus Fusarium oxysporum (or fusarium odoratissimum). TR4 is a soil-borne fungal disease. Fusarium fungus infests young roots or root bases, frequently through wounds. The disease spread to the rhizome (root-like stem), then to the rootstock and leaf bases.
Spread happens via vascular bundles, which become brown or dark red before becoming purple or black. The tips of older leaves become yellow. Within a few months, all except the youngest leaves turn yellow, wilt, collapse, and droop, covering the stalk with dead brown leaves. Although new shoots may grow at the base, all aboveground sections are eventually killed. These ultimate wilts and the plant dies, generally within a few years.
Panama TR4 is easily transmitted through humans, vehicles, machinery, animals, as well as the movement of infected banana plants, planting material, contaminated soil, and water. The Fusarium fungus gradually multiplies in the surrounding soil, although not unsafe for humans it prevents future plantings from thriving. The symptoms can only be seen externally after the disease has progressed. Therefore there is no practical way to detect the disease in banana plants until external symptoms are showing. There are no known fungicides that are effective against TR4 yet. Implementation of on-farm biosecurity and hygiene procedures, such as farm zoning to restrict movement into (and within) banana plantations, and the use of disinfectants in footbaths, as well as the cleaning of all equipment – workers, vehicles, machinery, and use of sterile planting material, are some of the biocontrol measures taken to reduce the spread of Fusarium wilt.
Panama disease became one of the first banana diseases to spread globally. It has returned, and there is no replacement banana as the Cavendish is no longer resistant. Despite Australia’s large presence of Fusarium wilt (145 years), the only effective approach of addressing the disease remains exclusion or early quarantine. A better knowledge of TR4 epidemiology and pathology is essential to protect current Cavendish plantings until viable resistant cultivars become available.
The banana’s triploid structure adds an undesired complexity of reproducing asexually. Because bananas of the same kind are genetically similar, if one tree in a plantation becomes infected, all of the other plants in the plantation are also vulnerable. This means that Panama disease could easily sweep over huge areas of susceptible host plants. Across many places, all of the trees were destroyed. Crossing domesticated bananas yields no seed, making this a poor choice. Genetic engineering can result in the generation of novel variants at a faster rate than traditional breeding procedures. This is a possible solution because there are over 1500 types of bananas and a variety of transgenes have been investigated, but only short-term results have been recorded.
Australian researchers discovered that introducing two separate genes to the genetic coding of Cavendish bananas protects the plants from TR4 but being a genetically modified (GM) crop, it might be a major barrier to its general adoption.
|MUSA GERMPLASM||LEVEL OF RESISTANCE||SCREENING LOCATION|
|CAM-020||R||University of Queensland, Australia|
This table shows the varieties of Banana Germplasm which have different levels of resistance to TR4. (HR- Highly resistant; R- Resistant)
Existing disease-resistant varieties are yet to make inroads into the international market, but The Honduras Foundation for Agricultural Research (FHIA) has spent more than three years working on developing a disease-resistant variety that is as close to the Cavendish as possible so that the world’s banana infrastructure does not have to be reshaped from the ground up. Nonetheless, this is a process that might take 15 to 20 years. Given the value of revenue coming from consumption and exporting the Cavendish, greater losses than the Gros Michel era (1950) are being suffered and are estimated to increase. A disease-resistant transgenic variety that will be accepted by the consumer is a critical need.