DANGEROUS INTERNATIONAL FOREST TREE DISEASES 63 



Literature : 



Butin, H. Die blatt-und rindenbewohnende Pilze der Pappel unter 



besonderer Berucksichtingung der Krankheitserreger. Mitt. 



Biol. Bund. Land. u. Forstwirt. Berlin-Dahlem 91, 64 pp. 1957. 

 F.A.O. Poplars in forestry and land use. Rome, 1958: 326-327 



(Section : Diseases of poplar, T. R. Peace, United Kingdom) 1958. 

 Servazzi, O. La defogliazione primaverile dei pioppi. Boll. Lab. 



R. Asservat. Fitopat. Torino. 1935. 

 Viennot-Bourgin, G. Les champignons parasites des plantes cul- 



tivees. T. II, Paris: 541-542. 1949. 



Leaf Rust of Poplars 



Melampsora allii-popuJina Kleb. This is a heteroecious rust occur- 

 ring mainly on leaves of black and balsam poplars. Uredia appear, 

 depending upon weather conditions, in mid- June and July on the under 

 surface of poplar leaves. Uredospores are elongated to oval, one- 

 celled, 23-38 X 11-18/*, thick-walled (2-4/*), spiny, yellow orange in 

 color, eatenu'late. Paraphyses are thick- walled (2-3/*), capitate or 

 rarely clavate, 50-60/* long, the swollen top measuring 14-22/* and the 

 stalk 3-5/1 in diameter. Telia in the form of dark-colored crusts ap- 

 pear on the undersurf ace of poplar leaves at the beginning of the winter 

 season. Teliospores are one-celled, prismatic, rounded in their upper 

 part, 35-60 X 6-1 0/*, with rather thick (1-2/*) and smooth walls. 

 They germinate the following spring in a probasidium, 20-40 X 7-1 1/*, 

 which later becomes four-celled, each cell producing a basidiospore. 

 Pycnial and aecial stage are found on different Allium species in the 

 early spring. Aecia are of the caeoma type. The aeciospores are 

 one-celled, rather thick-walled (1.5-2/*), oval, 15-20 X 10-15/*, with 

 gently roughened walls, orange red in color. 



The following are symptoms of the disease: (1) Bursting of rust- 

 colored pustules (uredia) on the underside of leaves on lower branches, 

 from mid-June in southern Europe and in July farther north. New 

 uredia appear during the growing season on the leaves of the upper 

 portion of the crown. The rusty color is due to uredospores. (2) 

 Building up of brownish crusts on fallen poplar leaves in autumn and 

 winter, also on the underside. These crusts comprise the telial stage. 



(3) Orange-reddish color of leaves and stems of Allium spp. in the 

 spring. This color is due to the formation of aecia with aeciospores. 



(4) Premature defoliation of poplars, starting usually at the end of 

 August in the case of heavy attacks. Trees of practically all ages are 

 susceptible. Areas with a high relative humidity are the most favor- 

 able for the spread of the fungus. Poor or inadequate soils seem to 

 offer better conditions for the evolution of the rust. 



There are three main disturbances of poplar plants resulting from 

 the fungus invasion : first, a considerable reduction in growth both in 

 diameter and height; second, frequently reported is a lowered resist- 

 ance of diseased individuals towards other pathogens, such as Dothi- 

 chiza populea; and finally, the defoliated snoots are more sensitive to 

 autumn frosts and are therefore frequently killed. Dying back of 

 poplars because of the rust is very rare and occurs primarily after con- 

 secutive heavy attacks on dry sites. 



Possibility of spread.— From the intercontinental point of view, 

 the spread of this rust is unlikely though it can take place through ship- 



