Why and How Can It Be a Global Threat?
A disease becomes a threat if the region in question grows susceptible cultivars and the climate also favours disease development. The other major factors contributing to the spread of a disease is a pathogen that is potent, fast evolving and adapts to non-traditional areas.
Favourable Climatic Conditions
Wheat blast requires concurrent heat and humidity to develop. Cardoso et al. (2008) observed the highest blast intensity at 30°C, which increased with wetting duration. The lowest severity was observed at 25°C with IO h of spike wetness. Irrespective of the temperature regime, a wetting duration of less than 10 h caused no blast, whereas a temperature regime of 25°C with a 40 h wetting duration caused the severity to exceed 85%. Similar conditions during the wheat life cycle exist in several parts of the world. Cardoso et al. (2008) developed a model that shows the blast intensity as a function of temperature and spike wetness duration. Urashima et al. (2007) studied the aerial dissemination of the blast pathogen to favourable climates. They employed molecular tools and concluded that pathogen clones could travel up to 1000 m from the inoculum source. Given that the global trade in wheat is a reality, experts had earlier warned (Peng et al., 2011) about a possible movement of blast from Latin America to similar regions of Africa and Asia. These fears came true when wheat blast was detected in Bangladesh in 2016 (Callaway, 2016). Islam et al. (2016) suspected that the wheat blast of Bangladesh was caused by a wheat-infecting South American lineage of the blast pathogen M. oryzae. If the pathogen shows such migratory capabilities in South Asia, it could jeopardise the food security of 300 million inhabitants of this region who consume about 100 million tonnes of wheat each year. The detection of blast in Bangladesh has already shown that the disease is capable of striking all parts of the globe from east to west wherever favourable climatic conditions exist. Even more worrying is the fact that fungicides, at best, offer only a partial defence (CIMMYT. 2019).
1.4.2 Pathogen is Evolving Fast and Evolving to Wide Spectrum