78 U.S. DEPT. OF AGRICULTURE MISC. PUB. 939 



species and uredinial and telial forms on poplar. A detailed account 

 of host range will be discussed in this short contribution. 



In contrast to other Melampsora species like M. larici-populina 

 Kleb. and M. larici-tremulae Kleb. causing premature defoliation of 

 poplar leaves, M. pinitorqua brings about considerable damage to 

 leaders of pines which become distorted and even may be killed. Shoots 

 of the current season are infected by basidiospores (sporidia), giving 

 existence to colorless pycnia (0), afterwards succeeded by orange- 

 yellow caeomata (I). In summer uredinia (II) and telia (III) are 

 produced on the alternate host. After hibernation of the dead, fallen 

 leaves these telia may germinate forming basidiospores. 



In the period 1953-54, Melampsora pinitorqua affected stands of 

 pine trees 5 to 7 years old grown in the nurseries of the Forest Re- 

 search Station at Wageningen.^ In close proximity of these pine trees, 

 poplars were cultivated, many* of which consisted of aspen and cross- 

 ings of aspen. From about the end of May the minute, colorless 

 pycnia, 4 to 5 days afterwards followed by caeomata, were developed 

 on the pine shoots. The number of caeomata considerably increased 

 during the months of June and July. 



Scots pine, mountain pine, and maritime pine appeared to be very 

 susceptible to the rust, whereas Corsican pine and Austrian pine, as 

 well as Pinus rigida Mill., demonstrated a striking resistance against 

 the parasite. In these species very few infections have been observed. 

 The following poplar species were grown in the vicinity : P. tremula 

 L., P. X canescens Sm., P. alba L., P. grandidentata Michx., P. 

 tremuloides Michx., and many other species of botanical interest of 

 sections Leuce Duby, Aigeiros Duby, and Tacamahaca Spach. 



In order to obtain more data on host range in the genus Populus 

 L., a number of species and clones of Leuce poplar have been investi- 

 gated. Caeomaspores of Melampsora pinitorqua collected from mari- 

 time pine have been used for inoculating discs of leaves floating on 

 water in petri dishes. A second series of discs has been used for com- 

 parison and inoculated with caeomaspores of Melampsora larici- 

 tremulae. 



Host plant: 



Populus tremula, no. 9 

 P. tremula , no. 23 

 P. canescens, no. 34 

 P. alba, no. 31 



P. alba, no. 37 + 



P. grandidentata, no. 85 — — 



P. grandidentata, no. 88 — + 



P. grandidentata, no. 99 — — 



P. tremuloides — ? 



P. tremuloides, no. 78 + + _ 



P. tremuloides, no. 79 — — 



P. tremuloides, no. 96 ++ + + 



Explanation : -f + + = very many uredinia ; + + =many ; -f =only 



few; — =none. 



Uredinial infection of the discs evidently demonstrated that Popu- 

 lus tremula, P. canescens, P. tremuloides, and less P. alba are hosts 



Melampsora 



Melampsora 



pinitorqua 



larici-tremulae 



+ + ' 



+ + + 



+ + 



+ + + 



+ + 



— 



+ 



— 



