The Watermark Disease of the Cricket Bat Willow (Salix Caerulea). Day, W. R. Clarendon Press.
The Watermark Disease of the Cricket Bat Willow (Salix Caerulea) [link]Paper  abstract   bibtex   
In this paper a full description is given of a disease, known locally in England as 'watermark', which appears as a die-back of the crown of Salix caerulea and S. alba and has caused serious losses to willow-growers in Essex and Hertfordshire. Up to the present, S.fragilis has remained free from attack. The external symptoms in the early stages (from May to July) consist in a general wilting, withering, and browning of leaves and tips of new shoots on one or more branches. After July, no further branches die back. Adventitious shoots were observed to develop in some cases on the dying and other branches, but these only survived for a short time on affected parts. Exudations of a thin, colourless, transparent, and sticky liquid may occur through wounds, usually those caused by insects, in the dying twigs. These have their origin in the wood and have been traced to bacterial causes, but are unlike the usual stiff, viscid exudation typical of other bacterial diseases, e.g., mulberry blight (Bacterium mori). No fungus was detected at this stage. In the subsequent stages, the bark of branches bearing withered leaves and twigs dies back gradually and the dying parts bear abundant pycnidia of the saprophytic fungus, Cytospora chrysosperma [Valsa sordida]. This, however, is regarded as a purely secondary organism. The disease continues to spread in subsequent seasons, but more slowly as time goes on. Death may occur within a year or two or may be delayed for a number of years, but trees once affected by the disease are of little value and recovery appears to be unknown. As regards internal symptoms, the bacterial infection which causes the discoloration arid subsequent blackening of the wood, to which the term 'watermark' is due, is limited chiefly to the last year's wood, but the stain can be traced throughout the dying branches and into the main stem of the tree. Radial spread is exceedingly slow, so that only a single annual ring of wood is usually involved for long periods. Ultimately even the roots may be reached, while the still living branches become progressively infected from below by extension through the main stem. In subsequent years the current season's wood in dying branches shows the watermark stain and this is also the case in the inain stem when death supervenes. While mechanical obstruction to the water flow is probably the main cause of the symptoms, the poisonous effects of the byproducts of the bacteria are apparent in the abnormal formation of tyloses and in premature leaf fall. The histological effects of the disease are dealt with in detail. They are marked chiefly by a mechanical blocking of the vessels by bacterial masses, by death of the wood parenchyma in the discoloured area, and by the disappearance of starch from the wood and bark of the affected branches. The brown pigment responsible for the change from light to dark brown of the watermarked area on exposure to air and in the later stages of the disease is attributed to the oxidation of a substance formed slowly in the wood and not directly produced by the pathogen. Observations indicate that the latter enters only by wounds in the branches. Isolation and inoculation experiments have established that the cause of the disease is a short, rod-like schizomycete, provisionally named Bacterium salicis n. sp. and described in detail. It is nonsporiferous, capsúlate, and measures 0.8 to 1.0 by 0.3 to 0.4 μ with- out the capsule. On beef-peptone-sucrose agar plates the colonies are round, convex, smooth, shining, white, and with a plain edge. It is regarded as a strictly vascular parasite. A wet sub-soil and close planting have been observed to encourage attack, and methods of control based on these observations are recommended. The destruction of diseased trees as soon as possible after the symptoms are observed should also serve to limit infection.
@book{dayWatermarkDiseaseCricket1924,
  title = {The Watermark Disease of the Cricket Bat {{Willow}} ({{Salix}} Caerulea)},
  author = {Day, W. R.},
  date = {1924},
  publisher = {{Clarendon Press}},
  location = {{Oxford}},
  url = {http://www.cabdirect.org/abstracts/19251100597.html},
  abstract = {In this paper a full description is given of a disease, known locally in England as 'watermark', which appears as a die-back of the crown of Salix caerulea and S. alba and has caused serious losses to willow-growers in Essex and Hertfordshire. Up to the present, S.fragilis has remained free from attack. 

The external symptoms in the early stages (from May to July) consist in a general wilting, withering, and browning of leaves and tips of new shoots on one or more branches. After July, no further branches die back. Adventitious shoots were observed to develop in some cases on the dying and other branches, but these only survived for a short time on affected parts. Exudations of a thin, colourless, transparent, and sticky liquid may occur through wounds, usually those caused by insects, in the dying twigs. These have their origin in the wood and have been traced to bacterial causes, but are unlike the usual stiff, viscid exudation typical of other bacterial diseases, e.g., mulberry blight (Bacterium mori). No fungus was detected at this stage. 

In the subsequent stages, the bark of branches bearing withered leaves and twigs dies back gradually and the dying parts bear abundant pycnidia of the saprophytic fungus, Cytospora chrysosperma [Valsa sordida]. This, however, is regarded as a purely secondary organism. The disease continues to spread in subsequent seasons, but more slowly as time goes on. Death may occur within a year or two or may be delayed for a number of years, but trees once affected by the disease are of little value and recovery appears to be unknown. 

As regards internal symptoms, the bacterial infection which causes the discoloration arid subsequent blackening of the wood, to which the term 'watermark' is due, is limited chiefly to the last year's wood, but the stain can be traced throughout the dying branches and into the main stem of the tree. Radial spread is exceedingly slow, so that only a single annual ring of wood is usually involved for long periods. Ultimately even the roots may be reached, while the still living branches become progressively infected from below by extension through the main stem. In subsequent years the current season's wood in dying branches shows the watermark stain and this is also the case in the inain stem when death supervenes. 

While mechanical obstruction to the water flow is probably the main cause of the symptoms, the poisonous effects of the byproducts of the bacteria are apparent in the abnormal formation of tyloses and in premature leaf fall. 

The histological effects of the disease are dealt with in detail. They are marked chiefly by a mechanical blocking of the vessels by bacterial masses, by death of the wood parenchyma in the discoloured area, and by the disappearance of starch from the wood and bark of the affected branches. The brown pigment responsible for the change from light to dark brown of the watermarked area on exposure to air and in the later stages of the disease is attributed to the oxidation of a substance formed slowly in the wood and not directly produced by the pathogen. Observations indicate that the latter enters only by wounds in the branches. 

Isolation and inoculation experiments have established that the cause of the disease is a short, rod-like schizomycete, provisionally named Bacterium salicis n. sp. and described in detail. It is nonsporiferous, capsúlate, and measures 0.8 to 1.0 by 0.3 to 0.4 μ with- out the capsule. On beef-peptone-sucrose agar plates the colonies are round, convex, smooth, shining, white, and with a plain edge. It is regarded as a strictly vascular parasite. 

A wet sub-soil and close planting have been observed to encourage attack, and methods of control based on these observations are recommended. The destruction of diseased trees as soon as possible after the symptoms are observed should also serve to limit infection.},
  keywords = {*imported-from-citeulike-INRMM,~INRMM-MiD:c-13659445,erwinia-salicis,salix-alba,tree-diseases},
  pagetotal = {30},
  series = {Oxford {{Forestry Memoirs}} n. 3}
}
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