The wheat crop in Punjab -- the breadbasket of India -- and also in Pakistan, is vulnerable to air-borne attack by "stem rust" in the event of an outbreak of this disease in a place as far away as East Africa.This is the finding of the first-ever study aimed at identifying likely scenarios for the global spread of this devastating crop disease caused by a fungus called "Puccinia graminis".If this disease erupts in one location, the highly virulent strains of the fungus can spread to distant places through trillions of pathogenic fungal spores dispersed by winds across countries and continents.The incredibly deadly strain of stem rust Ug99 -- so called because it was first detected in Uganda in 1999 -- is considered a threat to global food security and has so far not been detected in India.The study -- by a team of scientists of the University of Cambridge, the UK Met Office, and the International Maize and Wheat Improvement Centre in Mexico (CIMMYT) -- helps to predict which areas are at risk so that precautions can be taken.The scientists adapted computer modeling systems to forecast when and how Ug99 and other strains are most likely to spread. The scientific team used field disease surveys from CIMMYT and weather data from the UK Met Office as key inputs for the modeling framework.Their findings, published in the journal Nature Plants, "quantifies for the first time the circumstances -- routes, timings and outbreak sizes -- under which dangerous strains of stem rust pose a threat from long-distance dispersal out of East Africa to the large wheat-producing areas in India and Pakistan".According to their report, Yemen acts as a "stepping stone" for transmitting the disease between continents. "The key scenario for disease spread is from Yemen directly to Pakistan or India. In case of a large outbreak in Eastern Yemen, results indicate a 30 per cent chance for transmission to occur.""Another important scenario for wheat rust spread is from Yemen through Middle Eastern countries, in particular Iran, to Central and South Asia," says the report."If Iran were to suffer a moderate outbreak of Ug99, then spores would likely spread to Afghanistan, and from there potentially further to the northern plains of Pakistan and India.""From our work, we now believe that if we start to see Ug99 or other new wheat rust strains take hold in Yemen, then action must be taken immediately to mitigate the risk of further spread (to India)."Though Ug99 strain had not been detected in India so far, the Indian Agricultural Research Institute in New Delhi had announced in 2008 that its scientists have developed several varieties of wheat crops that are immune to Ug99.