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Lethal yellowing | |
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Common names | Coconut lethal yellowing phytoplasma |
Causal agents | Phytoplasma sp |
Hosts | Arecaceae (palms) |
Vectors | planthoppers ( Haplaxius crudus ) |
EPPO Code | PHYP56 |
Distribution | Florida, parts of the Caribbean, parts of Australia and Central America, East Africa |
Lethal yellowing (LY) is a phytoplasma disease that attacks many species of palms, including some commercially important species, such as the coconut and date palm. In the Caribbean, it is spread by the planthopper Haplaxius crudus (former name Myndus crudus) which is native to Florida, parts of the Caribbean, parts of Australia and Central America. [1] The only effective cure is prevention, e.g., planting resistant varieties of coconut palm and preventing a park-like or golf-course-like environment which attracts the planthopper.[ citation needed ] Some cultivars, such as the Jamaica Tall coconut cultivar, nearly died out because of lethal yellowing. Heavy turf grasses and similar green ground cover attracts the planthopper to lay its eggs there, and the nymphs develop at the roots of these grasses. The planthoppers' eggs and nymphs can pose a great threat to coconut-growing countries' economies, especially ones into which grass seeds for golf courses and lawns are imported from the Americas.
It is not clearly understood how the disease was spread to East Africa, as the planthopper Haplaxius crudus is not native to East Africa. The most likely explanation is that it was imported with grass seed from Florida that was used to create golf courses and lawns in beach resorts. There is a direct connection between green lawns and the spread of lethal yellowing in Florida. Even so-called 'resistant cultivars' such as the Malayan Dwarf or the Maypan hybrid between that dwarf and the Panama Tall were never claimed to have a 100% immunity.
The nymphs of the planthoppers develop on the roots of grasses, hence areas of grass in the vicinity of palm trees are connected with the spread of this phytoplasma disease. The problem arose as a direct result of using coconut and date palms for ornamental and landscaping purposes in lawns, golf courses and gardens, together with these grasses. When these two important food palms were grown in traditional ways (without grasses) in plantations and along the shores, the palm groves were not noticeably affected by lethal yellowing. There is no evidence that disease can be spread when instruments used to cut an infected palm are then used to cut or trim a healthy one.[ citation needed ] Seed transmission has never been demonstrated, although the phytoplasma can be found in coconut seednuts, but phytosanitary quarantine procedures that prevent movement of coconut seed, seedlings and mature palms out of an LY epidemic area should be applied to grasses and other plants that may be carrying infected vectors.
Beside coconut palm (Cocus nucifera), more than 30 palm species have also been reported as susceptible to lethal phytoplasmas around the globe. [2]
The coconut tree is a member of the palm tree family (Arecaceae) and the only living species of the genus Cocos. The term "coconut" can refer to the whole coconut palm, the seed, or the fruit, which botanically is a drupe, not a nut. The name comes from the old Portuguese word coco, meaning "head" or "skull", after the three indentations on the coconut shell that resemble facial features. They are ubiquitous in coastal tropical regions and are a cultural icon of the tropics.
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Sod, also known as turf, is the upper layer of soil with the grass growing on it that is often harvested into rolls.
Phytoplasmas are obligate intracellular parasites of plant phloem tissue and of the insect vectors that are involved in their plant-to-plant transmission. Phytoplasmas were discovered in 1967 by Japanese scientists who termed them mycoplasma-like organisms. Since their discovery, phytoplasmas have resisted all attempts at in vitro culture in any cell-free medium; routine cultivation in an artificial medium thus remains a major challenge. Phytoplasmas are characterized by the lack of a cell wall, a pleiomorphic or filamentous shape, a diameter normally less than 1 μm, and a very small genome.
Maypan is an F1 hybrid coconut palm that was developed by the Research Department of the Coconut Industry Board of Jamaica to be resistant to Lethal Yellowing disease. It was created experimentally in 1962 by cross pollinating two varieties of Cocos nucifera and, after extensive disease exposure and yield performance trials, was named and released in 1974 when a suitable method of mass controlled pollination had been devised. A DwarfxTall hybrid, the Malayan Dwarf seed parents, grown in an isolated seed garden and kept constantly emasculated, are regularly pollinated by blowing a mixture of talc and pollen collected from selected palms of a variety known locally as Panama Tall. This combination gives the Maypan an LY disease resistance approaching that of the Malayan Dwarf and much of the windstorm tolerance of the Panama Tall. It grows to approximately 18 meters in height. The LY resistance of the Maypan, of both of its parents, and of other coconut varieties generally, has been called into question since the 1990s but Maypan, and F1 hybrids using the same types of parents, are still the planting material of choice in the Caribbean and Latin American countries where LY occurs.
A planthopper is any insect in the infraorder Fulgoromorpha, in the suborder Auchenorrhyncha, a group exceeding 12,500 described species worldwide. The name comes from their remarkable resemblance to leaves and other plants of their environment and that they often "hop" for quick transportation in a similar way to that of grasshoppers. However, planthoppers generally walk very slowly. Distributed worldwide, all members of this group are plant-feeders, though few are considered pests. The infraorder contains only a single superfamily, Fulgoroidea. Fulgoroids are most reliably distinguished from the other Auchenorrhyncha by two features; the bifurcate ("Y"-shaped) anal vein in the forewing, and the thickened, three-segmented antennae, with a generally round or egg-shaped second segment (pedicel) that bears a fine filamentous arista.
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Elm yellows is a plant disease of elm trees that is spread by leafhoppers or by root grafts. Elm yellows, also known as elm phloem necrosis, is very aggressive, with no known cure. Elm yellows occurs in the eastern United States, and southern Ontario in Canada. It is caused by phytoplasmas which infect the phloem of the tree. Similar phytoplasmas, also known confusingly as 'Elm yellows', also occur in Europe. Infection and death of the phloem effectively girdles the tree and stops the flow of water and nutrients. The disease affects both wild-growing and cultivated trees.
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Haplaxius crudus is a planthopper species in the genus Haplaxius.
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