Division: Oomycota (water molds)
The water molds appear to have been derived from a brown algae which lost it's ability to photosynthesize..
The water molds possess several features in common with the brown algae: oogamous eggs, cellulosic cell walls, zoospores with two flagella (produced at various stages of their life cycles) and a predominately diploid life cycle.
* Order: Saprolegniales
Water molds occurring in mostly freshwater habitats and top layers of moist soils; some cause disease in fish and destroy fish roe in commercial hatcheries; others causes root rot in food crops.
Saprolegnia water mold forming large white masses on the head and back of a salmon.
* Order: Peronosporales
Terrestrial fungi; develop their entire life cycle on living hosts and cannot be grown in laboratory culture. Of great economic importance, two of which have had a great impact on human affairs. Both Phytophthora infestans and Plasmopara viticola pass their entire life cycle inside the tissues of their plant hosts and produce sporangia on the host surface.
Phytophora infestans: please read !
Fungus Blight is Threatening Potato Crops Around the World Developing countries face the greatest risk of a potato blight.
By WARREN E. LEARY Special to The New York Times
WASHINGTON, Oct. 23, 1993. Scientists say variants of the fungus that caused the Irish potato blight of the 1840's are spreading throughout the world, threatening a crop that is a staple in many countries. Agricultural experts are calling for an international research effort to thwart the new fungal variants, which are well-established throughout Europe and into Russia, as well as in Mexico and South American countries including Ecuador, Brazil and Argentina. Infestations are also being reported in potato-growing regions of the United States, Canada, Africa, Japan and Korea, the experts said this week.
Scientists to Meet
Modern fungicides could theoretically prevent the fungal disease, known as potato late blight, from causing widespread shortages, scientists said, but the effects could be more drastic in developing countries where potatoes have become an increasingly important crop and such chemical remedies are not as readily available. "All indications are that this new form of late blight is spreading around the world, and is more aggressive and harder to control than its predecessors," Dr. Hubert Zandstra, director general of the International Potato Center in Peru, said. Dr. Zandstra said scientists from around the world would meet in Mexico in February to organize an international research program on the problem. He said a foundation had provided money to start the effort, but that it needed support from the United States and other wealthy nations, as well as industry, to find solutions like developing potatoes with strong resistance to many variants of the fungus. The greatest risk is to agriculture in developing countries, where potato production is growing faster than that of any other staple crop except wheat, Dr. Zandstra said in an interview.0 The new blight could reduce prospects for increasing food supplies in areas such as India and Africa, where there are few resources to buy more fungicides and equipment to use them. In addition, he said, the new threat could set back efforts to reduce the use of toxic chemicals in agriculture. "We're not in the situation of the 1840's, facing famine, because we do have the chemicals," Dr. Zandstra said. "But we know the damage these chemicals cause."
Blight Came From Mexico
Experts said the new threat, made up of fungicide-resistant variants of the common blight fungus known as A1, and a related, possibly more potent type called A2, came from Mexico. Potato late blight is caused by the fungus Phytophthora infestans, which thrives in cool, moist conditions and is spread by contact or wind-blown spores. The disease, which can destroy a field in days, causes mottled, dark lesions on leaves and stems from which develop a white, velvety growth that kills the plant. Blighted potatoes develop a dark, corky rot and appear dehydrated. "This disease is remarkably explosive," said Dr. William E. Fry, professor of plant pathology at Cornell University. "An affected field looks like it has been burned."
A World Priority The fungus primarily reproduces asexually, which limits its genetic variation and makes it more likely to be killed by cold winter weather. But Dr. Fry said that when the Al and A2 types exist in the same place, they mate sexually, producing hard-hulled spores that can survive in soil for months and survive winter weather. Dr. John Niederhauser of the University of Arizona, who won the World Food Prize in 1990 for his work to increase potato production in developing countries, said that cultivating new potatoes with durable resistance to blight should be a world priority.
"There has been a world growth in potato production, and finding a new potato with resistance is so important if we are going to feed the growing population of the developing world," he said in a telephone interview. "Forty years ago, 90 percent of potato growth was in the industrialized world, and today, 72 percent is in industrial countries and 28 percent in the developing world," he said. "China, for instance, is now the largest potato producer in the world." Thin-skinned potatoes are not very hardy and, because they are susceptible to diseases and pests, already require higher levels of chemical pesticides and fungicides than any other food crop, Dr. Niederhauser said. "Just when people were starting to use fewer chemicals to grow potatoes, this blight will force them to use more," he said.