Plant disease outbreaks caused crop losses in 2007

Environment News Service: A year-end report from the International Society for Infectious Diseases shows the pattern of plant diseases around the world. While many diseases are spreading, there is some good news - grapevine leaf rust, caused by a wind borne fungus, has been successfully eradicated in Australia.

Also in Australia, a citrus canker eradication program is almost complete, although citrus canker and greening diseases continue to spread in the United States. Citrus greening was reported for the first time from Pakistan. Australian sugar growers are struggling with sugarcane smut, which has spread to all the major cane growing areas within 18 months of introduction of the pathogen into the country. Caused by the fungus Ustilago scitaminea, sugarcane smut was discovered in 1877 in South Africa. The use of resistant varieties is an approach to smut control that has succeded in Florida.

A controversy regarding the exclusion of New Zealand pome fruit by Australia to prevent the introduction of fireblight has been taken to the World Trade Organization. Rice viruses and their insect vectors were rampant in parts of Asia.

Asian soybean rust was first reported in Ghana, the Democratic Republic of Congo, and Canada in 2007, and was found in four more states in the United States than in 2006. Asian soybean rust, caused by the fungus Phakopsora pachyrhizi, is one of the most destructive diseases of soybean. Banana bacterial Xanthomonas wilt appears out of control in Africa with a disease focus in Uganda.

Outbreaks of coffee wilt, leaf rust, and berry disease have affected crops in Africa. Cocoa black pod and swollen shoot diseases are causing serious crop losses in West Africa. Cassava mosaic disease remains a serious threat to food security in Africa. Resistant germplasm is being distributed to farmers in affected countries. Sugarcane orange rust was reported for the first time in the Western hemisphere in the United States. Banana bunchy top virus is re-emerging in Hawaii.

Potato late blight is causing concern in many countries due to emerging new strains with increased virulence and multiple fungicide resistances. A major outbreak has affected crops in India.

A breakdown of resistance to lethal yellowing disease was observed in Malayan dwarf coconut hybrids. This jeopardizes replanting programs in areas affected by the disease. The mechanism of the resistance breakdown is unknown. Fungal diseases of vegetable, cereal and root crops, and grapevines were of concern in Europe due to warm and humid weather patterns in 2007.

Wheat stem rust strain Ug99 jumped the Red Sea and spread to Yemen. An even more virulent variant emerged in Kenya, and now an international research alliance was formed to screen for resistant germplasm.

These diseases are tracked by the International Society for Infectious Diseases' Program for Monitoring Emerging Diseases, an electronic outbreak reporting system that monitors infectious diseases globally.