A heteroecious parasite is one that requires at least two host

Host (biology)

In biology, a host is an organism that harbors a parasite, or a mutual or commensal symbiont, typically providing nourishment and shelter. In botany, a host plant is one that supplies food resources and substrate for certain insects or other fauna...

s. The primary host is the host in which the parasite spends its adult life; the other is the secondary host. Both the primary host and an unrelated alternate host are required for the parasite to complete its life cycle. This can be contrasted with an autoecious parasite which can complete its life cylce on a single host species. Many rust fungi are prime examples of a heteroecious life cylce.

Parasitic heteroecious fungi include

• Gymnosporangium
  Gymnosporangium
  Gymnosporangium is a genus of heteroecious plant-pathogenic fungi which alternately infect members of the family Cupressaceae, primarily species in the genus Juniperus , and members of the family Rosaceae in the subfamily Maloideae...
  
  (Cedar-apple rust); the juniper
  Juniper
  Junipers are coniferous plants in the genus Juniperus of the cypress family Cupressaceae. Depending on taxonomic viewpoint, there are between 50-67 species of juniper, widely distributed throughout the northern hemisphere, from the Arctic, south to tropical Africa in the Old World, and to the...
  
   is the primary (telial
  Teliospore
  Teliospore is the thick-walled resting spore of some fungi , from which the basidium arises.-Development:They develop in telia ....
  
  ) host and the apple
  Apple
  The apple is the pomaceous fruit of the apple tree, species Malus domestica in the rose family . It is one of the most widely cultivated tree fruits, and the most widely known of the many members of genus Malus that are used by humans. Apple grow on small, deciduous trees that blossom in the spring...
  
  , pear
  Pear
  The pear is any of several tree species of genus Pyrus and also the name of the pomaceous fruit of these trees. Several species of pear are valued by humans for their edible fruit, but the fruit of other species is small, hard, and astringent....
  
   or hawthorn
  Crataegus
  Crataegus , commonly called hawthorn or thornapple, is a large genus of shrubs and trees in the rose family, Rosaceae, native to temperate regions of the Northern Hemisphere in Europe, Asia and North America. The name hawthorn was originally applied to the species native to northern Europe,...
  
   is the secondary (aecial) host
• Cronartium ribicola (White pine blister rust); the primary host are white pines
  Pinus classification
  There are three main subgenera of Pinus, the subgenus Strobus , the subgenus Ducampopinus , and the subgenus Pinus...
  
  , and currants
  Ribes
  Ribes is a genus of about 150 species of flowering plants native throughout the temperate regions of the Northern Hemisphere. It is usually treated as the only genus in the family Grossulariaceae. Seven subgenera are recognized....
  
   the secondary.
• Hemileia vastatrix (Coffee rust); Primary host is coffee plant; Unknown alternate host
• Puccinia graminis (Stem rust of wheat and Kentucky bluegrass); Primary hosts include: Kentucky bluegrass, barley, and wheat; Common barberry is the alternate host.
• Puccinia coronata (Crown Rust of Oats and Ryegrass); Oats are the primary host; Rhamnus spp. (Buckthorn) is alternate host.
• Phakopsora meibomiae and P. pachyrhizi (Soybean Rust); Primary host is soybean and various legumes. Unknown alternate host.

History

The phenomenon of heteroecy was first discovered by A.S. Ørsted

Anders Sandøe Ørsted (botanist)

Anders Sandøe Ørsted, also written as Anders Sandoe Oersted or Anders Sandö Örsted was a Danish botanist, mycologist, zoologist and marine biologist. He was nephew of the brothers physicist H.C...

 in 1863.

• Ørsted, A.S. (1963) Om Sygdomme hos Planterne, som foraarsages af Snyltesvampe, navnlig om Rust og Brand og om Midlerne til deres Forebyggelse. Kjøbenhavn
  Copenhagen
  Copenhagen is the capital and largest city of Denmark, with an urban population of 1,199,224 and a metropolitan population of 1,930,260 . With the completion of the transnational Øresund Bridge in 2000, Copenhagen has become the centre of the increasingly integrating Øresund Region...
  
  .