Panama wilt infection has ruined banana plantations across the world for 50 years now. While scientists are trying to find solutions in natural fungi and gene editing, the answer might be in exploring banana’s forgotten cousins
The last flower has fallen in Sudarshan Maurya’s farm, located on the foothills of the Himalayas along the Nepal border. The cool and humid air of Khuniyaon block in Siddharthnagar district of Uttar Pradesh is just right for bananas, which have grown well rounded in Maurya’s farm and are ready to be picked.
Yet, a strange sense of uncertainty hangs over him. Every day he visits his five-hectare farm and carefully checks each plant and their leaves. At one end, rows of banana plants stand withered, discoloured and without any bunches.
“There are at least 5,000 such plants,” he says, with a heavy voice. “We knew would face losses because of the COVID-19 pandemic. But we were not prepared for a disaster like this. The leaves started turning yellow around May. By July, I could see them dying. I have sprayed all kinds of pesticides and other chemicals and spent almost Rs 12 lakh on their upkeep in the past one-and-a-half year. I don’t think I will recover the investment,” Maurya says.
The story is no different for the 20 other banana farmers in his village Belwa, who say their earnings have reduced to less than half. “We have been facing the infection for the past four to five years. But this year, it spread rapidly due to excessive rainfall,” says Chhotu Chaudhary, who owns about 1 ha. “A few plant scientists have visited our village in recent months. They say it is a type of cancer for which there is no cure.”
Siddharthnagar has been identified as one of the hotbeds of panama wilt infection, which is now pushing the world’s most cherished fruit to the verge of extinction. The infection is caused by a new strain of an old enemy — Fusraium oxysporum, a soil fungus.
The strain, described as F oxys-porum f sp cubense Tropical race 4, or simply TR4, has proved lethal to over 80 per cent of the 1,000-odd banana varieties available worldwide, including cavendish that represents the image of banana, provides half of the global supply and 99 per cent of export supply.
Since its appearance in Taiwan 50 years ago, the disease has spread to 18 countries, hopping continents — it was first reported in Asia in 1970, in Australia in 1997, in Africa in 2013 and in Latin America in 2019 — and is jeopardising the $25-billion banana industry.
But more than that, says the Food and Agriculture Organization (FAO), the infection has risked 400 million people for whom bananas and plantains are an inexpensive source of nutrition and a major source of livelihood.
The TR4 Task Force, created by FAO in 2013 to manage the outbreak, calls the strain “one of the most aggressive and destructive fungi in the history of agriculture and the world’s great-est threat to banana production”.
In India, the Indian Council of Agricultural Research (ICAR) conducted a survey soon after farmers in Bihar and Uttar Pradesh complained of a mysterious disease in 2017. Their initial mapping shows TR4 has so far infected over 3,000 ha of plantations in Bihar and 8,474 ha in Uttar Pradesh.
Worse, the outbreak has hit India, the largest producer and consumer of the fruit, at a time when it was getting ready to take on the export market. By 2018, the country’s total area under banana had doubled from 470,000 ha in 2000, says a market review published by FAO in February 2020.
TR4 is now forcing many farmers to give up banana altogether. ICAR scientists say while the disease has so far been reported by plantations growing cavendish varieties, such as Grand Naine (G9), Robusta, Bhusaval, Basrai and Shrimanth, traditional favourites like Malbhog and Rambhog are also susceptible to the infection.
These varieties are important sources of nutrition and income to small farmers and rural households.
Nagendra Maurya, a farmer from Totaha village in Sant Kabir Nagar district of Uttar Pradesh, explains the economics of traditional varieties. Farmers in his village grow G9, but they are still holding on to the traditional Rambhog, Padma 1, Padma 2 and Chinni kela. These can withstand heavy rains and wind, where as G9 falls off easily. Besides, traditional varieties are more in demand. Rambhog has markets in Delhi and Nepal.
“Scientists should develop a tissue culture variety for it to prevent the spread of infection,” says Nagendra. Besides, farmers at Tatoha say there is a difference in the way these varieties respond to Panama wilt. An infected G9 usually breaks off and gives a bad smell. Its stem becomes slimy. But traditional varieties do not break. Understanding these aspects will help assess TR4 better, infamous for its stealthy attacks.
Encased in a hard shell, its microscopic spores can spread across the world by hitching rides on anything from the farm worker’s boots, vehicle tyres to infected planting material or contaminated soil and water. While one microscopic spore is enough to kill an entire plant, it can survive for as many as 40 years in the soil.
Once in contact with the host plant, it produces thread-like hyphae that enter the roots through natural openings and wounds. The hyphae then grow through the corm into the vascular system, preventing movement of water and nutrients. Eventually, the plant wilts and dries.
An alert by the government of Queensland, Australia, which has been grappling with the infection for over 20 years, states there is currently no practical way to detect the disease until external symptoms start showing. It cannot be eliminated from the soil using fungicides or fumigants. FAO estimates if left unchecked, TR4 could destroy a majority of banana plantations by 2040.
Replay of history
Fusarium oxysporum has made a similar attempt to annihilate the fruit in the past. It was early 1870s. A young American sailor, Lorenzo Dow Baker, had just returned from Jamaica with green bananas. As the variety, Gros Michel, turned yellow gold, it became the favourite of the Americans, and Baker set the foundation of the modern banana production industry. But soon, a lethal blight colonised plantations in Panama.
It was by Race 1, one of the four strains of F oxysporum. Over the next few decades, the strain spread and wiped Gros Michel out of each export plantation on Earth by the 1950s.
This prompted the industry, already hooked to profits from large-scale monoculture production, to scramble for an alternative. It found solace in the less sweeter and less sturdier cavendish, which was left unscathed by Race 1. So, does this mean we can now replace cavendish with yet another resistant variety?
Well, there lies the catch. The world has nearly run out of alternatives since cavendish replaced the Gros Michel.
Banana is among the world’s oldest domesticated crop. It has descended from two wild varieties — Musa acuminata and Musa balbisiana — that originally grew in Southeast Asia and contained hard seeds. These propagated sexually by seeds and asexually by suckers.
Over tens of thousands of years, random mutations led to the evolution of seedless fruits, which were more edible. Our early agriculturalists domesticated these sterile mutants by propagating them vegetatively, through suckers.
While this helped banana rise to top the list of most consumed and traded fruit, it came at the cost of genetic diversity. Today, plantations are filled with genetically identical clones, produced in laboratories. They have a uniform cultivation cycle, produce identical fruits and, in case of an infestation, get simultaneously wiped out.
This trait of banana failed Gros Michel, and is now acting against cavendish. After the 1950s, as the industry ramped up its plantations it produced more sterile cavendish clones. Today, cavendish accounts for over 41 per cent of bananas grown worldwide, and for 60 per cent in top producing countries.
Its ubiquity can be gauged from the fact that even subsistence farmers now grow cavendish, making the hunt for resistant varieties an arduous task. Though developing hybrids is a common way of improving disease resistance in plants, it is complex for banana, which begins with first finding traces of fertility in its varieties.
FAO’s TR4 Task Force says the most effective approach is to contain the fungus as soon as it is detected and prevent its spread. In 2018, Australia tried putting in place biosecurity measures to halt the spread of TR4.
It introduced strict rules to prevent foreign soil from entering the country. Infested farms were fenced and quarantined. Farm owners were directed to ensure distance between plants and disinfect any equipment or vehicle that came in contact with the infected soil. The practices were audited by biosecurity officers at regular intervals. It worked well, but only for a while.
So in August 2019, when the fungus was reported for the first time on banana plantations in northeastern La Guajira, Colombia, it sounded the death knell for the fruit. Colombia is the fourth largest exporter of banana. The government declared it a national emergency. Its neighbours closed borders with it.
Together, Latin America and the Caribbean are the world’s largest exporting region, particularly cater-ing to the demand of EU and the US. While the fungus does not seem to have spreaded beyond La Guajira, the event has given new urgency to the efforts to prevent the scourge.
Race to save banana
One of the successful trials to stave off the infection is going on in India. For the past few months, every Sunday Bipin Singh prepares a solution to the exact specification of T Damodaran, principal scientist, at the Central Soil Salinity Research Institute (CSSRI), Lucknow, and pours it around the banana plants on his 0.5-ha farm in Dumari kala village in Bihar’s Sitamarhi district.
“It acts like a healing potion,” says Singh, who started growing bananas three years ago. “Last year 100 plants got infected with Panama wilt which cost me Rs 30,000. That’s when I contacted CSSRI officials. All my plants turned green within two months of applying their formulation,” he says.
Damodaran says the formulation is a novel strain of another fungus, Tricoderma EC, which acts as a bio fungicide against TR4. By creating an envelop around the roots, it first checks the entry of TR4 hyphae into the plant’s vascular system.
Then it triggers an immune response in the tree which releases an anti-fungal chemical that inhibits its growth. The plant thus gets back its vitality. Developed as a joint effort by CSSRI and the Central Institute of Sub-tropical Hotriculture (CHI), headed by Shailendra Rajan.
Both are under ICAR; their scientists have named the formulation ICAR-FUSICONT and claim to have revived 110 ha of severely affected banana plantations in Bihar and Uttar Pradesh. “In the process, we have restored an income of Rs 16.33 crore among farmers,” he says.
Simultaneously, the team is working on bio-immunisation technology that will make the plants resistant to TR4. The technology is similar to vaccination in humans. The bio-immune plants are prepared by injecting bioactive components into plant tissues during tissue culture. Under first phase trial, they have planted 3,000 bio-immune cultivars in TR4-infested field in Sohawal district of Uttar Pradesh.
“The plants are now four months old and growing healthy even without application of FUSICONT. If the crop survives the disease up to October, the technology will be first of its kind in the world. It would help revive more areas with moderate supplementation of the FUSICONT formulation,” says Damodaran.
But industry is restless
In several countries, where banana is the backbone of export earnings, the industry and governments are in a hurry to engineer the uber-banana through a mix of approaches.
In July, soon after Colombia declared national emergency to contain TR4, James Dale, a biotechnologist at the Queensland University of Technology in Brisbane, was flooded with enquiries about a variety that he and his team developed by inserting a gene from the wild banana Musa acuminate malaccensis.
Dale is now conducting a field trial of the transgenic cavendish on land infected with TR4 in northern Australia.
China, severely affected by TR4 since early 2000s, has developed five resistant varieties, using another technique — chemical mutagenesis. Under the process, scientists use chemicals, gamma rays, or X-rays to speed up the natural process of mutation and create plants with random mutations.
The breeder then chooses the one with desired traits and uses it to produce new varieties. Two of its varieties, ZJ4 and Baxi, have shown complete resistance. The Philippines is also in advanced stages of developing resistant varieties using mutagenesis through gamma irradiation.
Industries are using even more advanced techniques. In August, Elo Life Systems, a US food and agriculture firm, and the Dole Food Company, one of the world’s top banana suppliers, announced a partnership to develop multiple varieties resistant to fusarium wilt.
Elo plans to use its proprietary gene-editing technology — a homing endonuclease-based platform found naturally in primitive plants and algae — to cut out faulty DNA or insert new genetic material.
In the UK, start-up Tropic Biosciences has joined the race with its novel GEiGS (gene editing induced gene silencing) technique. Gilad Gershon, chief executive officer of the firm says, “We are the leaders in the space with over 75 professions working on banana genetics. We were already working to improve the quality of the fruit, for example improving its shelf life. Now we are developing varieties resistant to Panama disease. It will be commercially available in 3-4 years.”
So are we there yet?
It is difficult to predict. Crops, whether developed through genetic modification, mutagenesis or gene editing, have long been controversial for their effect on health and the environment. GM crops have faced public pushback around the world.
The EU has restrictive rules against GM crops. Recently, it said it would treat gene-edited crops and organisms obtained by mutagenesis at par with GMOs. Besides, none of these techniques address the basic flaw in commercial banana that over and again pushes it to the verge of extinction — commercial plants are genetically identical and cannot defend themselves against Panama disease.
Even if uber-bananas get to rule the market for a while, they would be clones of each other and knocked out by any other pathogen, which too are mutating and evolving outside laboratories.
R Thangavelu, scientist at the National Research Centre for Banana (NRCB) in Tamil Nadu, says Race 1 has already mutated. “In Theni district of Tamil Nadu, we found G9 being infected by Race 1. TR4 strain in India is also different from the strain damaging plantations elsewhere in the world. As of now, TR4 is more active in northern India where cavendish is dominant.
“In southern parts, Race 1 is causing Panama wilt in traditional varieties. But we have observed that two varieties, red banana and nendran, do not get affected by Panama wilt.”
Being the cradle of banana, genetic diversity of edible banana species in the country is vast. Even though cavendish provides 65 per cent of the commercially grown bananas, the remaining comes from nearly 20 traditional varieties. There are at least 320 other varieties grown on a small scale.
“There is an urgent need to identify and promote varieties that are naturally resistant to TR4. Growing a mix of varieties with different degrees of resistance and crop rotation with other crops like paddy, sugarcane, onion or pomegranate will reduce the incidence of the disease compared to growing the same cultivars for a longer period in the same field,” says S Uma, director, NRCB.
With inputs from Vivek Mishra in Siddharthnagar, Uttar Pradesh and Snigdha Das in New Delhi
This was first published in Down To Earth’s print edition (dated 1-15 October, 2020)
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