Manihot esculenta, commonly called cassava, manioc, or yuca, is a woody shrub of the spurge family, Euphorbiaceae, native to South America, from Brazil and parts of the Andes. Although a perennial plant, cassava is extensively cultivated as an annual crop in tropical and subtropical regions for its edible starchy root tuber, a major source of carbohydrates. Cassava is predominantly consumed in boiled form, but substantial quantities are used to extract cassava starch, called tapioca, which is used for food, animal feed, and industrial purposes. The Brazilian farinha, and the related garri of West Africa, is an edible coarse flour obtained by grating cassava roots, pressing moisture off the obtained grated pulp, and finally drying it.
Whiteflies are Hemipterans that typically feed on the undersides of plant leaves. They comprise the family Aleyrodidae, the only family in the superfamily Aleyrodoidea. More than 1550 species have been described.
Plant viruses are viruses that affect plants. Like all other viruses, plant viruses are obligate intracellular parasites that do not have the molecular machinery to replicate without a host. Plant viruses can be pathogenic to vascular plants.
The silverleaf whitefly is one of several species of whitefly that are currently important agricultural pests. A review in 2011 concluded that the silverleaf whitefly is actually a species complex containing at least 40 morphologically indistinguishable species.
Begomovirus is a genus of viruses, in the family Geminiviridae. They are plant viruses that as a group have a very wide host range, infecting dicotyledonous plants. Worldwide they are responsible for a considerable amount of economic damage to many important crops such as tomatoes, beans, squash, cassava and cotton. There are 445 species in this genus.
Maize streak virus (MSV) is a virus primarily known for causing maize streak disease (MSD) in its major host, and which also infects over 80 wild and domesticated grasses. It is an insect-transmitted pathogen of maize in the genus Mastrevirus of the family Geminiviridae that is endemic in sub-Saharan Africa and neighbouring Indian Ocean island territories such as Madagascar, Mauritius and La Reunion. The A-strain of MSV (MSV-A) causes sporadic maize streak disease epidemics throughout the maize-growing regions of Africa. MSV was first described by the South African entomologist Claude Fuller who referred to it in a 1901 report as "mealie variegation".
Cassava mosaic virus is the common name used to refer to any of eleven different species of plant pathogenic virus in the genus Begomovirus. African cassava mosaic virus (ACMV), East African cassava mosaic virus (EACMV), and South African cassava mosaic virus (SACMV) are distinct species of circular single-stranded DNA viruses which are transmitted by whiteflies and primarily infect cassava plants; these have thus far only been reported from Africa. Related species of viruses are found in India and neighbouring islands, though cassava is cultivated in Latin America as well as Southeast Asia. Nine species of cassava-infecting geminiviruses have been identified between Africa and India based on genomic sequencing and phylogenetic analysis. This number is likely to grow due to a high rate of natural transformation associated with CMV.
Cassava green mottle virus (CGMV) is a plant pathogenic virus of the family Secoviridae. Pathogens:
Cucumber mosaic virus (CMV) is a plant pathogenic virus in the family Bromoviridae. This virus has a worldwide distribution and a very wide host range, having the reputation of the widest host range of any known plant virus. It can be transmitted from plant to plant both mechanically by sap and by aphids in a stylet-borne fashion. It can also be transmitted in seeds and by the parasitic weeds, Cuscuta sp. (dodder).
Indian cassava mosaic virus(ICMV) is a plant pathogenic virus of the family Geminiviridae. It affects cassava (Manihot esculenta) in India and certain other countries. It is considered to be an invasive species.
Tomato yellow leaf curl virus (TYLCV) is a DNA virus from the genus Begomovirus and the family Geminiviridae. TYLCV causes the most destructive disease of tomato, and it can be found in tropical and subtropical regions causing severe economic losses. This virus is transmitted by an insect vector from the family Aleyrodidae and order Hemiptera, the whitefly Bemisia tabaci, commonly known as the silverleaf whitefly or the sweet potato whitefly. The primary host for TYLCV is the tomato plant, and other plant hosts where TYLCV infection has been found include eggplants, potatoes, tobacco, beans, and peppers. Due to the rapid spread of TYLCV in the last few decades, there is an increased focus in research trying to understand and control this damaging pathogen. Some interesting findings include the virus being sexually transmitted from infected males to non-infected females, and an evidence that TYLCV is transovarially transmitted to offspring for two generations.
Sweet potato mild mottle virus (SPMMV) is a plant pathogenic virus of the family Potyviridae.
Orthotospovirus is a genus of negative-strand RNA viruses, in the family Tospoviridae of the order Bunyavirales, which infects plants. Tospoviruses take their name from the species Tomato spotted wilt orthotospovirus (TSWV) which was discovered in Australia in 1919. TSWV remained the only known member of the family until the early 1990s when genetic characterisation of plant viruses became more common. There are now at least twenty species in the genus with more being discovered on a regular basis. Member viruses infect over eight hundred plant species from 82 different families.
Cassava brown streak virus disease (CBSD) is a damaging disease of cassava plants, and is especially troublesome in East Africa. It was first identified in 1936 in Tanzania, and has spread to other coastal areas of East Africa, from Kenya to Mozambique. Recently, it was found that two distinct viruses are responsible for the disease: cassava brown streak virus (CBSV) and Ugandan cassava brown streak virus (UCBSV). Both have (+)ss RNA genomes, belong to the genus Ipomovirus in the family Potyviridae, and produce generally similar symptoms in infected plants. Root rot renders the cassava tuber inedible, resulting in severe loss of economic value; therefore, current research focuses on achieving cultivars that do not develop the necrotic rot. This disease is considered to be the biggest threat to food security in coastal East Africa and around the eastern lakes.
High Plains wheat mosaic emaravirus (WMoV), or High Plains virus (HPV) or Maize red stripe virus (MRSV/MRStV) is the causative agent of High plains disease of maize and wheat. It is spread by wheat curl mite, Aceria tosichella, which also transmits Wheat streak mosaic virus. The mite's ability to transmit a number of different viruses to cereal crops make it an economically important agricultural pest. In late June 2017 this virus was first detected in Canada, in Alberta. The Alberta samples were 99% similar to those in the USA. As Wheat streak mosaic virus is already present in Alberta, and coinfection with these two causes even more severe damage, this could cause much higher yield losses.
Squash mosaic virus (SqMV) is a mosaic virus disease common in squash plants and other plants, including melons, of the family Cucurbitaceae. It occurs worldwide. It is transmitted primarily by beetles, including the leaf beetle, spotted cucumber beetle, and 28-spotted ladybird beetle, as well as some other beetles. Plants are infected by the saliva expelled by the beetles as they feed upon the plant. The beetles acquire the virus by feeding upon an infected plant and can retain the virus in their bodies for up to 20 days. Unlike some other mosaic viruses that infect squashes, SqMV is not spread by aphids. In melons it can be spread by seeds. The results are dark green mosaic, blistering, vein clearing, yellowing of leaves, and hardening. Symptoms include "pronounced chlorotic mottle, green veinbanding, and distortion of leaves". Fruits of infected plants are also affected, becoming mottled and misshaped. There are two strains of this virus: strain 1 has a greater effect on melons than squash while the opposite is true of strain 2.
Maize lethal necrosis disease is a viral disease affecting maize (corn) predominantly in East Africa, Southeast Asia and South America, which was recognised in 2010. It is caused by simultaneous infection with two viruses, MCMoV and any of several Potyviridae.
Cassava brown streak virus is a species of positive-strand RNA viruses in the genus Ipomovirus and family Potyviridae which infects plants. Member viruses are unique in their induction of pinwheel, or scroll-shaped inclusion bodies in the cytoplasm of infected cells. Cylindrical inclusion bodies include aggregations of virus-encoded helicase proteins. These inclusion bodies are thought to be sites of viral replication and assembly, making then an important factor in the viral lifecycle. Viruses from both the species Cassava brown streak virus and Ugandan cassava brown streak virus (UCBSV), lead to the development of Cassava Brown Streak Disease (CBSD) within cassava plants.
Laura Boykin is an American computational biologist who uses supercomputing and genomics to help farmers in Sub-Saharan Africa. She has studied the evolution of the agricultural pest whitefly and identified genetic differences between various species. She works with African scientists to develop computing and genomics skills across the continent, and is a Senior TED fellow.
Elijah Miinda Ateka is a Professor of Plant Virology at the Jomo Kenyatta University of Agriculture and Technology. He is involved with the diagnosis and characterisation of the sweet potato virus and the cassava virus, and is part of the Cassava Virus Action Project (CVAP).
