BREEDING RUST RESISTANT POPLARS 421 



P. tricJzoaarpa and from the hybrid P. trickocarna x P. nigra. According 

 to Taris , this rust is limited to Asia while Peace (1962) reports that it 

 is found in North Africa and Argentina as well. 



MELAMPSORA LARICI-POPULINA KLEB. 



The aecia are formed on different Larix spp. Peace (1962) reports 

 this rust occurs in Europe, the Near East and Argentina. According to 

 Taris, it exists in Eurasia, North Africa, North and South America. A 

 high number of clones of the four main species and their hybrids are 

 susceptible to this rust. 



MELAMPSORA MAGNUSIANA KAGN. 



~ : :~: '. \ ::-. :' :-r ~::J:-.£ Lour, and "orylus spp. are the aecia] hosts of 

 this rust which, according to Peace (1962) , is limited to aspen and white 

 poplars in Europe and Japan, but, according to Taris also affects ?. 

 alba L., P. trerrula L., and ?. nigra in Europe. 



MELAMPSORA MEDUSAE THUM 



The aecial spores are formed on Larix spp. Peace (1962) reports 

 black and balsam poplars are susceptible to this rust in North America 

 and France, while Taris does not mention this species for France. 



MELAMPSORA OCCIDENT ALIS JACKS. 



This rust is found in North America on black and balsam poplars. 



MELAMPSORA ROSTRUPII V\AGN . 



The aecial spores are formed on Mercurialie perenn-is L. Gremmen 

 (1954) isolated it on white poplars. According to Peace (1962), it 

 occurs on white poplars and only rarely on black and balsam poplars in 

 Europe. According to Taris, M. rostrupii affects a large series of species 

 and clones of white poplars, P. balsamifera Muenehh., P. nigra and many 

 different euramericana hybrids in Europe but rarely in North America. 



NORMAL LIFE -CYCLE OF POPLAR RUSTS 



The species of Melarrpsora normally have two host plants. The uredia 

 and the telia are formed on the poplar leaves, whereas the aecia are 

 formed on an alternate host. 



The orange or yellow uredia occur in midsummer, usually on the under 

 surface, but sometimes on the upper surface of the poplar leaves. The 

 uredospores infect other young poplar leaves and are responsible for the 

 quick spreading of the disease all over the nurseries and plantations. 

 The brown telia are formed in the autumn, mostly on the upper side of the 

 poplar leaves. The sporidia infect the alternate host and yellow aecia 

 appear during late spring. Even in our experimental nursery, where for 

 some years very susceptible poplar plants have been interplanted with 



