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The disease is named after one of the most characteristic symptoms of an advanced infection, when the leaves become progressively dwarfed, upright and bunched at the top of the plant, with wavy and chlorotic margins that tend to turn necrotic. The first symptoms are dark green streaks on the lower portion of the leaf’s midrib and later on the secondary veins.
The virus is also transmitted through infected plant suckers and other plant components used in banana propagation but is not sap transmissible (Magee, 1927).
Banana aphids have a worldwide distribution with a host range that includes ) are also colonized (Wardlaw, 1961).
In studies of outbreaks of bunchy top in commercial banana plantations, Allen (1978b, 1987) showed that the average distance of secondary spread of the disease by aphids was only 15.5-17.2 m.
Allen and Barnier (1977) showed that if a new plantation was located adjacent to a diseased plantation, the chance of spread of bunchy top into the new plantation within the first 12 months was 88%.This chance was reduced to 27% if the plantations were separated by 50-1000 m and to less than 5% if they were 1000 m apart.Aphid numbers decrease during periods of drought (Wardlaw, 1961).Transmission efficiency for individual aphids has been reported as ranging from 46 to 67% (Magee, 1927; Wu and Su., 1990a; Hu et al., 1996) and the virus is more efficiently acquired by nymphs than by adults (Magee, 1940).
The disease was first identified in Fiji in 1889, and has spread around the world since then (Global Invasive Species Database, 2005).
The virus itself, which was originally classified as a luteovirus, was isolated in the late 1980s and reassigned to the Nanoviridae family in the genus ) in a persistent manner (Magee, 1927).