Top dying disease is a disease that affects ''

Heritiera fomes ''Heritiera fomes'' is a species of mangrove tree in the family Malvaceae. Its common names include sunder, sundri, jekanazo and pinlekanazo. It is the dominant mangrove tree species of the Sundarbans of Bangladesh and India, and comprises about ...

'', a species of

mangrove A mangrove is a shrub or tree that grows in coastal saline or brackish water. The term is also used for tropical coastal vegetation consisting of such species. Mangroves are taxonomically diverse, as a result of convergent evolution in severa ...

tree known as "sundri", a characteristic tree of the estuarine complex of the Ganges–Brahmaputra Delta in Bangladesh and

West Bengal West Bengal (, Bengali: ''Poshchim Bongo'', , abbr. WB) is a state in the eastern portion of India. It is situated along the Bay of Bengal, along with a population of over 91 million inhabitants within an area of . West Bengal is the fou ...

. Although an increase in certain trace elements in the sediment deposited where these trees grow may be a factor in the incidence of the disease, its cause has not been fully established. __TOC__

History

About 63% of the trees growing in the

Sundarbans Sundarbans (pronounced ) is a mangrove area in the delta formed by the confluence of the Padma, Brahmaputra and Meghna Rivers in the Bay of Bengal. It spans the area from the Baleswar River in Bangladesh's division of Khulna to the Hooghly R ...

are ''Heritiera fomes''. Sporadic instances of top dying disease had been noticed in these trees earlier in the twentieth century but the disease became more acute and extensive after about 1970. An inventory of trees in the Sundarbans in 1985 recorded 45 million diseased trees with nearly half of these having more than half their crown affected. No causal agent has been discovered and the dieback is thought to be the result of stressful conditions, perhaps caused by an increase in the heavy metal concentration of the sediment deposited in the delta.

Symptoms

The uppermost parts of the tree are affected first with loss of leaves and dieback of branches in the

crown A crown is a traditional form of head adornment, or hat, worn by monarchs as a symbol of their power and dignity. A crown is often, by extension, a symbol of the monarch's government or items endorsed by it. The word itself is used, partic ...

. One or more knot-like swellings may develop on affected branches. Lower branches are progressively affected over time. Wood-boring insects and fungi invade the diseased wood and the tree eventually dies.

References

{{reflist Plant pathogens and diseases Mangroves Sundarbans