Lettuce is an annual plant of the family Asteraceae. It is most often grown as a leaf vegetable, but sometimes for its stem and seeds. Lettuce is most often used for salads, although it is also seen in other kinds of food, such as soups, sandwiches and wraps; it can also be grilled. One variety, the celtuce, is grown for its stems, which are eaten either raw or cooked. In addition to its main use as a leafy green, it has also gathered religious and medicinal significance over centuries of human consumption. Europe and North America originally dominated the market for lettuce, but by the late 20th century the consumption of lettuce had spread throughout the world. As of 2017, world production of lettuce and chicory was 27 million tonnes, 56% of which came from China.
A heteroecious parasite is one that requires at least two hosts. The primary host is the host in which the parasite spends its adult life; the other is the secondary host. Both hosts are required for the parasite to complete its life cycle. This can be contrasted with an autoecious parasite which can complete its life cycle on a single host species. Many rust fungi have heteroecious life cycles:
Rusts are plant diseases caused by pathogenic fungi of the order Pucciniales.
Lactuca, commonly known as lettuce, is a genus of flowering plants in the family Asteraceae. The genus includes at least 50 species, distributed worldwide, but mainly in temperate Eurasia.
The name Indian lettuce has been used to refer to a number of plants used as leaf vegetables used by Native American or Indian people, including but likely not limited to:
Lactuca virosa is a plant in the Lactuca (lettuce) genus, often ingested for its mild analgesic and sedative effects. It is related to common lettuce, and is often called wild lettuce, bitter lettuce, laitue vireuse, opium lettuce, poisonous lettuce, tall lettuce, great lettuce or rakutu-karyumu-so.
Stem rust, also known as cereal rust, black rust, red rust or red dust, is caused by the fungus Puccinia graminis, which causes significant disease in cereal crops. Crop species that are affected by the disease include bread wheat, durum wheat, barley and triticale. These diseases have affected cereal farming throughout history. The annual recurrence of stem rust of wheat in North Indian plains was discovered by Prof. K.C. Mehta. Since the 1950s, wheat strains bred to be resistant to stem rust have become available. Fungicides effective against stem rust are available as well.
Wheat leaf rust is a fungal disease that affects wheat, barley, rye stems, leaves and grains. In temperate zones it is destructive on winter wheat because the pathogen overwinters. Infections can lead up to 20% yield loss, which is exacerbated by dying leaves, which fertilize the fungus. The pathogen is a Puccinia rust fungus. It is the most prevalent of all the wheat rust diseases, occurring in most wheat-growing regions. It causes serious epidemics in North America, Mexico and South America and is a devastating seasonal disease in India. P. triticina is heteroecious, requiring two distinct hosts.
Lactuca serriola, also called prickly lettuce, milk thistle, compass plant, and scarole, is an annual or biennial plant in the tribe Cichorieae within the family Asteraceae. It has a slightly fetid odor and is commonly considered a weed of orchards, roadsides and field crops. It is the closest wild relative of cultivated lettuce.
Puccinia striiformis var. striiformis is a plant pathogen. It causes stripe rust on wheat, but has other hosts as well. The species is common in Europe and in more recent years has become a problem in Australia. Infection can cause losses of up to 40%, and the fungus will infect both winter wheat and spring wheat. The taxonomy of Puccinia striiformis was revised in 2010. The commonly called stripe rusts on wheat and grasses were separated into four species based on molecular and morphological studies: Puccinia striiformis sensu stricto, Puccinia pseudostriiformis, Puccinia striiformoides and Puccinia gansensis
Puccinia asparagi is the causative agent of asparagus rust. It is an autoecious fungus, meaning that all stages of its life cycle – pycniospores, aeciospores, and teliospores – all develop upon the same host plant . Rust diseases are among the most destructive plant diseases, known to cause famine following destruction of grains, vegetables, and legumes. Asparagus rust occurs wherever the plant is grown and attacks asparagus plants during and after the cutting season. Asparagus spears are usually harvested before extensive rust symptoms appear. Symptoms are first noticeable on the growing shoots in early summer as light green, oval lesions, followed by tan blister spots and black, protruding blisters later in the season. The lesions are symptoms of Puccinia asparagi during early spring, mid-summer and later summer to fall, respectively. Severe rust infections stunt or kill young asparagus shoots, causing foliage to fall prematurely, and reduce the ability of the plant to store food reserves. The Puccinia asparagi fungus accomplishes this by rust lowering the amounts of root storage metabolites. The infected plant has reduced plant vigor and yield, often leading to death in severe cases. Most rust diseases have several stages, some of which may occur on different hosts; however, in asparagus rust all the life stages occur on asparagus. Because of this, many observers mistake the different stages of the Puccinia asparagi life cycle as the presence of different diseases. The effects of Puccinia asparagi are present worldwide wherever asparagus is being grown. Asparagus rust is a serious threat to the asparagus industry.
Puccinia coronata is a plant pathogen and causal agent of oat and barley crown rust. The pathogen occurs worldwide, infecting both wild and cultivated oats. Crown rust poses a threat to barley production, because the first infections in barley occur early in the season from local inoculum. Crown rusts have evolved many different physiological races within different species in response to host resistance. Each pathogenic race can attack a specific line of plants within the species typical host. For example, there are over 290 races of P. coronata. Crops with resistant phenotypes are often released, but within a few years virulent races have arisen and P. coronata can infect them.
Puccinia menthae is a fungal plant pathogen that causes rust on mint plants.
Puccinia thaliae is the causal agent of canna rust, a fungal disease of Canna. Symptoms include yellow to tan spots on the plant's leaves and stems. Initial disease symptoms will result in scattered sori, eventually covering the entirety of the leaf with coalescing pustulates. Both leaf surfaces, although more predominant on the underside (abaxial) of the leaf, will show yellow to brownish spore-producing these pustulate structures, and these are the signs of the disease. Spots on the upper leaf-surface coalesce and turn to brown-to-black as the disease progresses. Infection spots will become necrotic with time, with small holes developing in older leaves. These infected leaves eventually become dry and prematurely fall.
Lactuca canadensis is a species of wild lettuce known by the common names Canada lettuce, Canada wild lettuce, tall lettuce, and Florida blue lettuce. Its true native range is not clear, but it is considered to be a native of the eastern and central parts of North America. It naturalized in the western part of the continent as well as in Eurasia.
Wheat yellow rust, also known as wheat stripe rust, is one of the three major wheat rust diseases, along with stem rust of wheat and leaf rust.
Puccinia malvacearum, also known as hollyhock or mallow rust, is a species within the genus Puccinia known for attacking members of the family Malvaceae. An autoecious pathogen, it can complete its life cycle using a single host.
Puccinia poarum, the coltsfoot gall rust or meadow grass rust, is a plant pathogen. This fungal parasite forms a yellow to orange gall, 1–2 cm in diameter, on the underside of leaves of coltsfoot. It also infects, but does not gall grasses of the family Poaceae. P. poarum is a genetically diverse species that has been reported on at least seventy plant hosts.
Austropuccinia psidii, commonly known as myrtle rust, guava rust, or ʻōhiʻa rust; is a rust native to South America that affects plants in the family Myrtaceae. It is a member of the fungal complex called the guava rust group. The spores have a distinctive yellow to orange colour, occasionally encircled by a purple ring. They are found on lesions on new growth including shoots, leaves, buds and fruits. Leaves become twisted and may die. Infections in highly susceptible species may result in the death of the host plant.
Puccinia mariae-wilsoniae, commonly known as the spring beauty rust, is a species of rust fungus found in North America. A plant pathogen, it grows on the leaves of the spring beauty flowering plants Claytonia caroliniana and C. virginica.
