1 Institute of Microbiology and Virology of the National Academy of Sciences, Zabolotny str. 1 54, 252143, Kyiv, Ukraine; 2 Laboratory of forestry Acad.Sci of Russia, 143030, Moscow, Russia; 3Kyiv Taras Shevchenko University, pr.Akademika Glushkova, 2112, 252000, Kyiv, Ukraine

Background and objectives
In 1950-1960 forest shelter-belts were created in the large steppe and semi-desert regions consisting of different introduced trees and shrubs. Much prominence was given by specialists to the oak plantations which were transplanted in monoculture and with the other plants. During the last 10-15 years these plants began to die. The aim of our investigations was to reveal the reason for this phenomenon.

Results and conclussions
Investigation of the oak plantations revealed extensive drying of young shoots, which were injured by the coccids Asteroidiaspis guerecoia Bouche, As.variolosus Ratz and also by the miner Moritzielia corficalis Kalt. There were many necrotic oval brown spots in the places of the attachment of the coccids. The measurements of such zones varied from 5-10 mm up to several centimetres. The death of the bark leads to the formation of open and closed cankers on the shoots, which can heal or lead to the dying of the shoots.

Necrotic injuries envelop bark and wood. Through bacteriological analysis of necrotic zones (by methods /1/) of bark and wood we isolated pathogenic bacteria, which were identified as Pseudomonas syringae pv.syringae and P. cichorii accoding to /2/. In addition we isolated the less aggressive bacterium Erwinia spp.. Artificial infection of shoots and stems of the oak was achieved by introducing the bacteria P. syringae pv. syringae and P. cichori into mechanical injuries to the bark and wood. In the first year it was noted necrosis of bark or sometimes callus. Under affected bark we noted that the wood was coloured reddish-brown, yellow-brown and greyish-brown. Sometimes we noted developing of opene cankers. For a period of five years this disease made progress and led to the drying of the infected shoots. At the inoculation by the isolated strains P. syringae pv. syringae and P. cichorii we didn't reveal any difference in the symptoms of disease.

Thus the reason of the drying of the oak plantations in Kalmykhia is bacterial disease, caused by P. syringae pv.syringae and P. cichorii infecting the initial mechanical injuries made in the bark by the insects.

1. Gvozdyak R.l., Yakovieva L.M. 1980. Diagnostik of bacterial diseases of forest wood plants. Moscow. 32p. (in Russian).
2.Bergey's Manual of Systematic Bacteriology. - 9th ed., 1984, vol. 1, 964p.