420 V. STEENACKERS 



INTRODUCTION 



Melampsora species (Basidiomycetes , Uredinales) ,from all over the 

 world, produce similar disease symptoms on the leaves of species and 

 hybrid poplar clones. The rusts are without doubt among the most 

 dangerous poplar diseases. Many examples are reported in the literature 

 of heavy rust infections which result in early defoliation, reduction of 

 growth, and even dieback of young and old trees. 



At the same time, an early leaf fall has a marked influence on the 

 infection of the tree by Dothichiza populea Sacc. § Briard. Even if it 

 is possible to fight the disease by spraying with fungicides, breeding 

 resistant clones by selection and hybridization is by far the best and 

 cheapest way of controlling the disease in nurseries and plantations. 

 This paper deals with the state of knowledge in breeding of rust-resistant 

 clones of the poplar species Populus nigra L., P. deltoides Bartr., P. 

 trichocarpa Torrey $ Gray ex Hooker, P. maximowiozii Henry, and the 

 reciprocal hybrids. 



RUSTS OF POPLARS- -GEOGRAPHICAL DISTRIBUTION 



Based on field observations or artificial infection tests, different 

 authors have published more or less complete lists of the rust species, 

 their aecial and uredial hosts and their geographical distribution. 



A list for the Netherlands, based on his own observations, has been 

 published by Gremmen (1954) . Another list is given by Peace (1962) . 

 Hennebert (1964) and Veldeman (1964) have published lists of the most 

 common rust species occurring in Belgium. A more recent list for France 

 is published by Taris (1966) in his handbook "Poupliers et Populiculture" 



In Canada, Ziller (1965) has made controlled inoculation experiments 

 with rust species on various host plants. One conclusion of this work 

 was that Melampsora alhertensis Arth. would be reduced to synonymy with 

 M. medusae Thtlm. 



According to various authors clones of P. nigra, P. deltoides _, P. 

 trichocarpa, P. maximowiczii and the reciprocal hybrids are affected in 

 different degrees by the various rust species. But there always exists 

 a certain confusion concerning the identity of the rust species, the 

 alternate host plants, the poplar species and clones affected by each 

 rust species. Also, the geographical distribution of the rust species 

 is not always clear. 



MELAMPSORA ABIETIS-CANADENSIS (FARL.) C. A. LUDWIG 



MELAMPSORA ALLII-POPULINA KLEI 



Following Peace (1962), this rust lives on Tsuga spp . , aspen (P. 

 tremuloides Michx.), and white and balsam poplars, in North America. 



The aecia are formed on different Allium species. According to 

 Peace (1962) and Taris, this rust affects black and balsam poplars. 

 Gremmen (1954), in the Netherlands, has isolated this rust only on Section 

 Aegeiros Duby poplars. Veldeman (1964) isolated it in Belgium from 



