Wheat blast, a disease caused by the fungus Magnaporthe oryzae, was first discovered in Brazil in 1985. The disease spread rapidly and, by the early 1990s, had affected three million hectares of arable land, severely restricting the potential for wheat cultivation across South America. Wheat blast attacks the ears of wheat, shrivelling and deforming the grain just one week after symptoms first appear. Affected seeds become bleached and die before becoming wheat grains. It is spread by seed and infected leaf debris. The disease, previously only ever recorded in South America and the US state of Kentucky, appeared in Bangladesh in February 2016, marking the first outbreak of wheat blast in Asia to date. So far, it has affected 108,000 hectares of wheat fields in south-west Bangladesh. The projected financial loss due to wheat blast is estimated at 1,800 crore taka ($300 million). There are concerns that the attack in Bangladesh could lead to further outbreaks across Asia, particularly in India and Pakistan.
Agriculture employs 47 per cent of Bangladesh’s total labour force and comprises 16 per cent of GDP. Wheat is the second-largest cultivated grain in Bangladesh, grown across 4.3 lakh (430,000) hectares of land, and is vital to the food security and livelihoods of the Bangladeshi people. A subsistence farmer in the worst-hit regions is expected to harvest 80 per cent less wheat as a result of the outbreak. Wheat is an integral part of food security not just in Bangladesh, but also the wider Asian region. Across South Asia over 135 million tonnes of wheat is grown each year. An outbreak of wheat blast beyond Bangladesh’s borders would have a devastating effect on the South Asian region, whose inhabitants consume over 100 million tonnes of wheat each year.
Wheat blast thrives in warm and humid climates. February in Bangladesh saw unseasonal rains and higher temperatures, allowing the disease to proliferate. Similar climactic conditions feature across much of Asia, providing an ideal environment for the disease to spread. There is concern that wheat blast may spread to India, the second-largest producer of wheat worldwide. India has downplayed the threat, insisting its quarantine and breeding programmes are robust and effective at eliminating wheat blast. India’s major wheat-producing states are Punjab, Haryana and Uttar Pradesh, away from the Bangladeshi border. India has not yet ruled out a ban on the import of wheat from Bangladesh and is considering halting the cultivation of wheat in border areas of the eastern states of West Bengal and Assam if wheat blast in Bangladesh is not contained.
Pakistan is the eighth-largest producer of wheat worldwide. Agriculture comprises 25.5 per cent of GDP and employs 43.7 per cent of the labour force. Like Bangladesh, Pakistan’s food security, and the livelihoods of its people, would suffer immensely if wheat blast were to spread across its cultivated land. There are mounting concerns that, if the disease were to reach Pakistan, they would not have adequate surveillance or quarantine capabilities to control the disease.
The most immediate threat of wheat blast in Asia comes from Thailand, the Philippines and Vietnam. These countries import wheat from Brazil and may see presentations of the disease similar to that of Bangladesh if quarantine processes are not properly implemented.
The wheat blast fungus, Magnaporthe oryzae, belongs to the same species that causes rice blast, a similar disease that affects rice crops. The wheat blast pathogen, however, is a distinct population of Magnaporthe oryzae, the Triticum population, and does not cause the disease in rice. The same cannot be said for other crops, such as barley and maize, which can be infected by the Triticum population.
In the short-term, due quarantine protocol must be employed in countries moving wheat, alongside the effective surveillance of crops. Seeds to be planted in the next season should not be sourced from affected regions. Control of the date of wheat planting will help to prevent wheat blast by ensuring cultivation does not correspond with weather patterns conducive to disease growth. In the long term, developing improved wheat varieties that carry genetic resistant to Magnaporthe oryzae will drastically reduce the incidence of wheat blast. Research is currently underway, with resistant germplasms being tested in areas of South America that are still majorly affected. Given the short window between symptoms appearing and major damage, chemical interventions are impractical. Developing disease-resistant varieties of wheat is the best long-term strategy to control wheat blast.