Viroids are small single-stranded, circular RNAs that are infectious pathogens. Unlike viruses, they have no protein coating. All known viroids are inhabitants of angiosperms, and most cause diseases, whose respective economic importance to humans varies widely. A recent metatranscriptomics study suggests that the host diversity of viroids and other viroid-like elements is broader than previously thought and that it would not be limited to plants, encompassing even the prokaryotes.
Citrus is a genus of flowering trees and shrubs in the family Rutaceae. Plants in the genus produce citrus fruits, including important crops such as oranges, mandarins, lemons, grapefruits, pomelos, and limes.
Corymbia ficifolia, commonly known as red flowering gum, is a species of small tree that is endemic to the south-west of Western Australia. It has rough, fibrous bark on the trunk and branches, egg-shaped to broadly lance-shape adult leaves, flower buds in groups of seven, bright red, pink or orange flowers and urn-shaped fruit. It has a restricted distribution in the wild but is one of the most commonly planted ornamental eucalypts.
Citrus production encompasses the production of citrus fruit, which are the highest-value fruit crop in terms of international trade. There are two main markets for citrus fruit:
American sweetgum, also known as American storax, hazel pine, bilsted, redgum, satin-walnut, star-leaved gum, alligatorwood, or simply sweetgum, is a deciduous tree in the genus Liquidambar native to warm temperate areas of eastern North America and tropical montane regions of Mexico and Central America. Sweetgum is one of the main valuable forest trees in the southeastern United States, and is a popular ornamental tree in temperate climates. It is recognizable by the combination of its five-pointed star-shaped leaves and its hard, spiked fruits. It is currently classified in the plant family Altingiaceae, but was formerly considered a member of the Hamamelidaceae.
The blood orange is a variety of orange with crimson, near blood-colored flesh. It is one of the sweet orange varieties. It is also known as the raspberry orange.
The Pospiviroidae are a incertae sedis family of ssRNA viroids with 5 genera and 39 species, including the first viroid to be discovered, PSTVd, which is part of genus Pospiviroid. Their secondary structure is key to their biological activity. The classification of this family is based on differences in the conserved central region sequence. Pospiviroidae replication occurs in an asymmetric fashion via host cell RNA polymerase, RNase, and RNA ligase. Its hosts are plants, specifically dicotyledons and some monocotyledons.
Aegle marmelos, commonly known as bael, also Bengal quince, golden apple, Japanese bitter orange, stone apple or wood apple, is a species of tree native to the Indian subcontinent and Southeast Asia. It is present in India, Pakistan, Bangladesh, Sri Lanka, and Nepal as a naturalized species. The tree is considered to be sacred by Hindus and Buddhists.
A seedless fruit is a fruit developed to possess no mature seeds. Since eating seedless fruits is generally easier and more convenient, they are considered commercially valuable.
An orange, also called sweet orange to distinguish it from the bitter orange, is the fruit of a tree in the family Rutaceae. Botanically, this is the hybrid Citrus × sinensis, between the pomelo and the mandarin orange. The chloroplast genome, and therefore the maternal line, is that of pomelo. The sweet orange has had its full genome sequenced.
The citrange is a citrus hybrid of the sweet orange and the trifoliate orange.
Citrus tristeza virus (CTV) is a viral species of the genus Closterovirus that causes the most economically damaging disease to its namesake plant genus, Citrus. The disease has led to the death of millions of Citrus trees all over the world and has rendered millions of others useless for production. Farmers in Brazil and other South American countries gave it the name "tristeza", meaning sadness in Portuguese and Spanish, referring to the devastation produced by the disease in the 1930s. The virus is transmitted most efficiently by the brown citrus aphid.
Erythricium salmonicolor is a species of fungus in the family Corticiaceae. Basidiocarps are effused, corticioid, smooth, and pinkish and grow on wood. The fungus is a commercially significant plant pathogen which has become a serious problem, especially in Brazil. Erythricium salmonicolor causes Pink Disease, most commonly in Citrus, although E. salmonicolor has a wide host range including rubber and cacao trees. Pink Disease causes branch and stem die-back due to canker formation. The cankers are recognizable by gum exudation and longitudinal splitting of the bark.
Citrus australis, the Dooja, round lime, Australian lime or Australian round lime, is a large shrub or small tree producing an edible fruit. It grows in forest margins in the Beenleigh area and northwards, in Queensland, Australia.
Grafting or graftage is a horticultural technique whereby tissues of plants are joined so as to continue their growth together. The upper part of the combined plant is called the scion while the lower part is called the rootstock. The success of this joining requires that the vascular tissues grow together. The natural equivalent of this process is inosculation. The technique is most commonly used in asexual propagation of commercially grown plants for the horticultural and agricultural trades. The scion is typically joined to the rootstock at the soil line; however, top work grafting may occur far above this line, leaving an understock consisting of the lower part of the trunk and the root system.
Citrus psorosis ophiovirus is a plant pathogenic virus infecting citrus plants worldwide. It is considered the most serious and detrimental virus pathogen of these trees.
The hop stunt viroid is a viroid species that infects the common hop plant, citrus plants, grapevines, cucumber, and several Prunus species such as almond, apricot, plum, and peach. It is asymptomatic or latent in most host plants, but in some hosts it can cause stunting and other symphtoms. A study of HSVd-infected hops in the USA showed that the severity of yield reduction was highly dependent on the infected hop cultivar.
Citrus exocortis is a disease of citrus plants, caused by the Citrus exocortis viroid (CEVd). It can cause stunted growth and reduced yields in affected plants. The disease is also sometimes called "scalybutt". CEVd can also infect tomato plants. The resulting disease is sometimes called "tomato bunchy top disease".
Cadang-cadang is a disease caused by Coconut cadang-cadang viroid (CCCVd), a lethal viroid of several palms including coconut, African oil palm, anahaw, and buri. The name cadang-cadang comes from the word gadang-gadang that means dying in Bicol. It was originally reported on San Miguel Island in the Philippines in 1927/1928. "By 1962, all but 100 of 250,000 palms on this island had died from the disease," indicating an epidemic. Every year one million coconut palms are killed by CCCVd and over 30 million coconut palms have been killed since Cadang-cadang was discovered. CCCVd directly affects the production of copra, a raw material for coconut oil and animal feed. Total losses of about 30 million palms and annual yield losses of about 22,000 metric tons of copra have been attributed to Cadang-cadang disease in the Philippines.
